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What do red ants secrete while marching in a line, one after the other?

What do red ants secrete while marching in a line, one after the other?


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Red ants often move in a group, and seem to follow a trail one after the other.

Once, I rubbed a part of the path along which they were moving and surprisingly found that the successive ants roaming around the rubbed region became confused as to where to go. It seems that the preceding ants secrete some kind of chemical (hormones, excretory wastes or body secretions) which guide the other ants to follow it. What is this secretion?


The simple answer is that ants secrete a substance called trail pheromone as they forage for food and each ant follows the trail of trail pheromone that is laid down by the preceding ant.

The term 'trail pheromone' can be a bit indistinct, however. Rather than consisting of a single chemical, trail pheromone is composed of many different chemicals, the exact compositions of which appear to be used deliberately to deliver complex information about the details of a given foraging site.

In the linked paper, the authors suggest that the

use of several trail pheromones that differ in their persistence provides memory over differing time scales. In particular, a non-volatile pheromone can provide a longer-term memory, while a volatile pheromone can allow rapid choice among potential feeding locations by quickly 'forgetting' depleted locations.

This means that ants may be able to use pheromones to assemble a sort of "collective memory" for the colony, concerning the locations of food and the quantity of food found at each location.


Ants' movements hide mathematical patterns

Argentine ants ( Linepithema humile ). Credit: © Lek Khauv (Licensed CC - BY-NC)

When ants go exploring in search of food they end up choosing collective routes that fit statistical distributions of probability. This has been demonstrated by a team of mathematicians after analysing the trails of a species of Argentine ant. Studies like this could be applied to coordinate the movement of micro-robots in cleaning contaminated areas for example.

Scientists have yet to discover the mechanisms explaining how flocks of birds, shoals of fish, lines of ants and other complex natural systems organise themselves so well when moving collectively.

To tackle this problem, researchers from Spain and the U.S. have analysed the movements of Argentine ants (Linepithema humile, an invasive species in many parts of the world) while they forage or explore an empty space (a petri dish) and propose a model explaining how they form their routes.

The authors, whose study has been published in the journal Mathematical Biosciences, started by observing the behaviour of ants individually and subsequently as a collective group. They recorded all their movements and based on these experiments, detected that the random changes in the direction of the insects follow mathematical patterns.

"To be more specific, they are a mixture of Gaussian and Pareto distributions, two probability functions which are commonly used in statistics, and that in this case dictate how much the ant 'turns' at each step and the direction it will travel in," María Vela Pérez, researcher at the European University in Madrid and co-author of the study, explains to SINC.

The scientists had already verified in previous studies that the 'persistence' of ants, or rather, their tendency not to change their direction while there are no obstacles or external effects, together with the 'reinforcement' occurring in areas which they have already visited (thanks to the pheromone trail that they leave) are two factors which determine their routes as they forage.

Concentration of pheromone (more in red color) after 10,000 time steps (6.67min.), 20,000 time steps (13.33min.) and 40,000 time steps (26.67min.). Credit: S. Garnier, M. Vela-Pérez et al.

Now, with this data they have been able to create the model describing the collective movement of the ants on a surface. The numerical simulations on the computer show the formation of ramified patterns very similar to those observed in the petri dishes during the real experiment with ants.

Applications in small robots

Aside from the mere biological interest, these advances could be applied in diverse technological fields. "For example, they could be used to design the coordination of a group of micro-robots or small robots to clean a contaminated area or other tasks," Vela Pérez points out.

The researcher reminds us that the study of the modelling, organisation and coordination of the animal behaviour is a clear example of multidisciplinary collaboration: "biologists participate to perform the experiments in the laboratory and provide real data, in coordination with mathematicians and physicists who propose and solve the models".

One of the researchers who has participated in this study is Marco A. Fontelos from the Institute of Mathematical Sciences (ICMAT), who has also co-authored another study regarding the formation of lines of ants that "can be characterised as bifurcations or trailblazing when the concentration of pheromones exceeds a certain value". The theoretical model is based on partial differential equations and the details are published in the Journal of Mathematical Analysis and Applications.

Marco A. Fontelos, Avner Friedman. "A PDE model for the dynamics of trail formation by ants". Journal of Mathematical Analysis and Applications 425 (1): 1-19, 2015.


Contents

The specific epithet of the red imported fire ant, invicta, derives from Latin, and means "invincible" or "unconquered". [5] [6] [7] The epithet originates from the phrase Roma invicta ("unconquered Rome"), used as an inspirational quote until the fall of the Western Roman Empire in 476 AD. The generic name, Solenopsis, translates as "appearance" or "face" from Ancient Greek. It is a compound of two Ancient Greek words–solen, meaning "pipe" or "channel", and opsis, meaning "appearance" or "sight". [8] [9] The ant is commonly known as the "red imported fire ant" (abbreviated as RIFA), because of the burning sensation caused by its sting. [10] [11] Alternative names include: the "fire ant", "red ant" or "tramp ant". [12] [13] In Brazil, locals call the ant toicinhera, which derives from the Portuguese word toicinho (pork fat). [14]

The red imported fire ant was first described by Swiss entomologist Felix Santschi in a 1916 journal article published by Physis. [15] Originally named Solenopsis saevissima wagneri from a syntype worker collected from Santiago del Estero, Argentina, Santschi believed the ant was a variant of S. saevissima the specific epithet, wagneri, derives from the surname of E.R. Wagner, who collected the first specimens. [16] The type material is currently housed in Naturhistorisches Museum Basel, Switzerland, but additional type workers are possibly housed in the Muséum national d'histoire naturelle, Paris. [17] In 1930, American myrmecologist William Creighton reviewed the genus Solenopsis and reclassified the taxon as Solenopsis saevissima electra wagneri at infrasubspecific rank, noting that he could not collect any workers that referred to Santschi's original description. [18] In 1952, the S. saevissima species complex was examined and, together with nine other species-group names, S. saevissima electra wagneri was synonymised with S. saevissima saevissima. [19] This reclassification was accepted by Australian entomologist George Ettershank in his revision of the genus and in Walter Kempf's 1972 catalogue of Neotropical ants. [20] [21]

In 1972, American entomologist William Buren described what he thought was a new species, naming it Solenopsis invicta. [22] Buren collected a holotype worker from Cuiabá in Mato Grosso, Brazil, and provided the first official description of the ant in a journal article published by the Georgia Entomological Society. He accidentally misspelled invicta as invica above the description pages of the species, although it was clear that invicta was the intended spelling because of the constant use of the name in the article. [23] The type material is currently housed in the National Museum of Natural History, Washington, D.C. [22]

In a 1991 review of the species complex, American entomologist James Trager synonymised S. saevissima electra wagneri and S. wagneri together. [23] Trager incorrectly cites Solenopsis saevissima electra wagneri as the original name, erroneously believing that the name S. wagneri was unavailable and used Buren's name S. invicta. Trager previously believed that S. invicta was conspecific with S. saevissima until comparing the material with S. wagneri. Trager notes that though S. wagneri has priority over S. invicta, the name was never used above infrasubspecific rank. The use of the name since Santschi has not been associated with collected specimens, and as a result is nomen nudum. [23] In 1995, English myrmecologist Barry Bolton corrected Trager's error, recognising S. wagneri as the valid name and synonymised S. invicta. [24] He states that Trager wrongfully classified S. wagneri as an unavailable name and cites S. saevissima electra wagneri as the original taxon. He concludes that S. wagneri is, in fact, the original name and has priority over S. invicta. [24] [25]

In 1999, Steve Shattuck and colleagues proposed conserving the name S. invicta. [17] Since the first description of S. invicta, over 1,800 scientific papers using the name were published discussing a wide range of topics about its ecological behaviour, genetics, chemical communication, economic impacts, methods of control, population, and physiology. They state that the use of S. wagneri is a "threat" to nomenclatural stability towards scientists and non-scientists taxonomists may have been able to adapt to such name change, but name confusion may arise if such case occurred. Due to this, Shattuck and his colleagues proposed the continued use of S. invicta and not S. wagneri, as this name has been rarely used between 1995 and 1998, over 100 papers were published using S. invicta and only three using S. wagneri. They requested that the International Commission on Zoological Nomenclature (ICZN) use plenary powers to suppress S. wagneri for the purpose of the Principle of Priority and not for the Principle of Homonymy. Furthermore, they requested that the name S. invicta be added to the Official List of Specific Names in Zoology and that S. wagneri be added to the Official Index of Rejected Invalid Specific Names in Zoology. [17] Upon review, the proposal was voted on by the entomological community and was supported by all but one voter. They note that there is no justification in suppressing S. wagneri instead, it would be better to give precedence to S. invicta over S. wagneri whenever an author treated them as conspecific. The ICZN would conserve S. invicta and suppress S. wagneri in a 2001 review. [26] Under the present classification, the red imported fire ant is a member of the genus Solenopsis in the tribe Solenopsidini, subfamily Myrmicinae. It is a member of the family Formicidae, belonging to the order Hymenoptera, an order of insects containing ants, bees, and wasps. [27]

Phylogeny Edit

The red imported fire ant is a member of the S. saevissima species-group. Members can be distinguished by their two-jointed clubs at the end of the funiculus in workers and queens, and the second and third segments of the funiculus are twice as long and broad in larger workers. Polymorphism occurs in all species and the mandibles bear four teeth. [22] The following cladogram shows the position of the red imported fire ant among other members of the S. saevissima species-group: [a] [28]

Solenopsis invicta

Phenotypic and genetic data suggest that the red imported fire ant and the black imported fire ant (Solenopsis richteri) differ from each other, but they do share a close genetic relationship. [29] [30] [31] [32] Hybridisation between the two ants occurs in areas where they make contact, with the hybrid zone located in Mississippi. Such hybridisation has resulted from secondary contact between these two ants several decades ago, when they first encountered each other in southern Alabama. [29] [33] Based on mitochondrial DNA, examined haplotypes do not form a monophyletic clade. Some of the examined haplotypes form a closer relationship to S. megergates, S. quinquecuspis and S. richteri than they do with other S. invicta haplotypes. The occurrence of a possible paraphyletic grouping suggests that the red imported fire ant and S. quinquecuspis are possible cryptic species groups composed of several species that cannot be distinguished morphologically. [32] [34]

Genetics Edit

Studies show that mitochondrial DNA variation occurs substantially in polygyne societies (nests with multiple queens), [35] but no variation is detected in monogyne societies (nests with a single queen). [36] Triploidy (a chromosomal abnormality) occurs in red imported fire ants at high rates (as high as 12% in non-reproductive females), which is linked to the high frequency of diploid males. [37] The red imported fire ant is the first species shown to possess a green-beard gene, by which natural selection can favour altruistic behaviour. Workers containing this gene are able to distinguish between queens containing it, and those that do not, apparently by using odour cues. The workers kill queens that do not contain the gene. [38] [39] In 2011, scientists announced they had fully sequenced the red imported fire ant genome from a male. [40]

Red imported fire ant workers range in size from small to medium, making them polymorphic. Workers measure between 2.4 and 6.0 mm (0.094 and 0.236 in). [41] The head measures 0.66 to 1.41 mm (0.026 to 0.056 in) and is 0.65 to 1.43 mm (0.026 to 0.056 in) wide. In the larger workers (as in the major workers), their heads measure 1.35 to 1.40 mm (0.053 to 0.055 in) and 1.39 to 1.42 mm (0.055 to 0.056 in) wide. The antenna scapes measure 0.96 to 1.02 mm (0.038 to 0.040 in) and the thoracic length is 1.70 to 1.73 mm (0.067 to 0.068 in). [22] The head becomes wider behind the eyes with rounded occipital lobes present, and unlike the similar-looking S. richteri, the lobes peak further than the midline, but the occipital excision is not as crease-like. The scapes in major workers do not extend beyond occipital peak by one or two scape diameters this feature is more noticeable in S. richteri. In medium-sized workers, the scapes reach the occipital peaks and exceed the rear border in the smallest workers. In small and medium workers, the head tends to have more elliptical sides. The head of small workers is wider out front than it is behind. [22] In the major workers, the pronotum does not have any angular shoulders, nor does it have any sunken posteromedian area. The promesonotum is convex and the propodeum base is rounded and also convex. The base and declivity are of equal length. The suture of the promesonotum is either strong or weak in larger workers. The petiole has a thick and blunt scale if observed from behind, it is not as rounded above in contrast to S. richteri, and sometimes it may be subtruncate. The postpetiole is large and broad, and in the larger workers, it is broader than its length. The postpetiole tends to be less broad in front and broader behind. On the rear side of the dorsal surface, a transverse impression is present. In S. richteri, this feature is also present but much weaker. [22]

The sculpture is very similar to S. richteri. [22] The punctures are from where pilosity arises, and these are often elongated on the dorsal and ventral portions of the head. On the thorax, striae are present, but they are less engraved with fewer punctures than in S. richteri. On the petiole, the punctates are located on the sides. The postpetiole, when viewed above, has a strong shagreen with distinct transverse punctostriae. The sides are covered in deep punctures, where they appear smaller but deeper. In S. richteri, the punctures are larger and more shallow. This gives a more opaque appearance to the surface. In some cases, punctostriae may be present around the rear portion. [22] The pilosity appears similar to that of S. richteri. These hairs are erect and vary in length, appearing long on each side of the pronotum and mesonotum on the head, the long hairs are seen in longitudinal rows. Numerous appressed pubescent hairs are on the petiolar scale this is the opposite in S. richteri, as these hairs are sparse. [22] Workers appear red and somewhat yellowish with a brown or completely black gaster. [15] Gastric spots are sometimes seen in larger workers, where they are not as brightly coloured as those in S. richteri. The gastric spot usually covers a small portion of the first gastric tergite. The thorax is concolorous, ranging from light reddish-brown to dark-brown. The legs and coxae are usually lightly shaded. The head has a consistent colour pattern in large workers, with the occiput and vertex appearing brown. Other parts of the head, including the front, genae, and the central region of the clypeus, are either yellowish or yellowish brown. The anterior borders of the genae and mandibles are dark-brown they also both appear to share the same coloured shade with the occiput. The scapes and funiculi range from being the same colour as the head or shares the same shade with the occiput. Light-coloured areas of the head in small to medium-sized workers is restricted to only the frontal region, with a dark mark resembling an arrow or rocket being present. On occasion, nests may have a series of different colours. For example, workers may be much darker, and the gastric spot may be completely absent or appear dark-brown. [22]

Queens have a head length of 1.27 to 1.29 mm (0.050 to 0.051 in) and a width of 1.32 to 1.33 mm (0.052 to 0.052 in). [22] The scapes measure 0.95 to 0.98 mm (0.037 to 0.039 in) and the thorax is 2.60 to 2.63 mm (0.102 to 0.104 in). The head is almost indistinguishable from S. richteri, but the occipital excision is less crease-like and the scapes are considerably shorter. Its petiolar scale is convex and resembles that of S. richteri. The postpetiole has straight sides that never concave, unlike in S. richteri where they concave. The thorax is almost identical, but the clear space between the metapleural striate area and propodeal spiracles is either a narrow crease or not present. The side portions of the petiole are punctate. The sides of the postpetiole are opaque with punctures present, but no irregular roughening is seen. The anterior of the dorsum is shagreen, and the middle and rear regions bear transverse puncto-striae. All these regions have erect hairs. The anterior portions of both the petiole and postpetiole have appressed pubescence that is also seen on the propodeum. The colour of the queen is similar to that of a worker: the gaster is dark brown and the legs, scapes, and thorax are light brown with dark streaks on the mesoscutum. The head is yellowish or yellowish-brown around the central regions, the occiput and mandibles are a similar colour to the thorax, and the wing veins range from colourless to pale brown. [22] Males appear similar to S. richteri, but the upper borders of the petiolar scales are more concave. In both species, the postpetiole's and petiole's spiracles strongly project. The whole body of the male is concolorous black, but the antennae are whitish. Like the queen, the wing veins are colourless or pale brown. [22]

The red imported ant can be misidentified as the similar-looking S. richteri. [22] The two species can be distinguished from each other through morphological examinations of the head, thorax, and postpetiole. In S. richteri, the sides of the head are broadly elliptical and the cordate shape seen in the red imported fire ant is absent. The region of the occipital lobes that are situated nearby the midline and occipital excision appear more crease-like in S. richteri than it does in the red imported fire ant. The scapes of S. richteri are longer than they are in the red imported fire ant, and the pronotum has strong angulate shoulders. Such character is almost absent in the red imported fire ant. A shallow but sunken area is only known in the larger workers of S. richteri, which is located in the posterior region of the dorsum of the pronotum. This feature is completely absent in larger red imported fire ant workers. The red imported fire ant's promesonotum is strongly convex, whereas this feature is weakly convex in S. richteri. Upon examination, the base of the propodeum is elongated and straight in S. richteri, while convex and shorter in the red imported fire ant. It also has a wide postpetiole with either straight or diverging sides. The postpetiole in S. richteri is narrower with converging sides. In S. richteri, the transverse impression on the posterodorsal portion of the postpetiole is strong, but weak or absent in the red imported fire ant. [22] As well as that, S. richteri workers are 15% larger than red imported fire ant workers, are blackish-brown, and have a yellow stripe on the dorsal side of the gaster. [42] [43]

Brood Edit

Eggs are tiny and oval-shaped, remaining the same size for around a week. After one week, the egg assumes the shape of an embryo and forms as a larva when the egg shell is removed. [44] Larvae measure 3 mm (0.12 in). [45] They show a similar appearance to S. geminata larvae, but they can be distinguished by the integument with spinules on top of the dorsal portion of the posterior somites. The body hairs measure 0.063 to 0.113 mm (0.0025 to 0.0044 in) with a denticulate tip. The antennae both have two or three sensilla. The labrum is smaller with two hairs on the anterior surface that are 0.013 mm (0.00051 in). The maxilla has a sclerotised band between the cardo and stipes. The labium also has a small sclerotised band. [45] The tubes of the labial glands are known to produce or secrete a proteinaceous substance that has a rich level of digestive enzymes, which includes proteases and amylases that function as an extraintestinal digestion of solid food. The midgut also contains amylases, roteases and upases. The narrow cells in its reservoir have little to no function in secretion. [46] The pupae resemble adults of any caste, except that their legs and antennae are held tightly against the body. They appear white, but over time, the pupae turns darker when they are almost ready to mature. [47]

Four larval instars have been described based on distinctive morphological characters. [44] [48] [49] The larvae of the minor and major workers are impossible to distinguish before the final instar, when size differences become apparent. [49] Upon pupation a wider head width difference between castes become more evident. Reproductive larvae are larger than worker larvae, and present discrete morphological differences in mouthparts. [49] Fourth-instar larvae of males and queens can be differentiated based on their relative shape and body coloration, [49] and also internal gonopodal imaginal discs can differ.

Polymorphism Edit

The red imported fire ant is polymorphic with two different castes of workers: minor workers and major workers (soldiers). Like many ants that exhibit polymorphism, young, smaller ants do not forage and tend to the brood, instead, while the larger workers go out and forage. [50] [51] [52] [53] In incipient colonies, polymorphism does not exist, but instead they are occupied by monomorphic workers called "minims" or "nanitics". The average head-width in tested colonies increases during the first six months of development. [54] [55] In five-year-old colonies, the head width of minor workers decreases, but for major workers, the head-width remains the same. The total weight of a major worker is twice that of a minor worker when they first arrive, and by six months, major workers are four times heavier than minor workers. Once major workers develop, they can make up a large portion of the workforce, with as many as 35% being major workers in a single colony. [54] This does not affect colony performance, as polymorphic colonies and nests with small workers produce broods at roughly the same rate, and polymorphism is not an advantage or disadvantage when food sources are not limited. However, polymorphic colonies are more energetically efficient, and under conditions where food is limited, polymorphism may provide a small advantage in brood production, but this depends on the levels of food stress. [56]

As worker ants grow to larger sizes, the shape of the head changes, due to the head length growing at the same time as the total body length, and the head width may grow by 20%. The length of the antennae only grows slowly the antennae may only grow 60% longer by the time the body doubles its length, thus the relative antennal length decreases by 20% as the length of the body doubles. [55] All individual legs of the body are isometric with body length meaning that even when the length of the body doubles, the legs will also double. However, not all of the legs are the same length the prothoracic portion accounts for 29% of leg length, the mesothoracic 31%, and the metathoracic 41%. The first two pairs of legs are of equal length to one another, whereas the final pair is longer. [55] Overall, the morphological appearance of a worker changes dramatically when it grows larger. The head exhibits the greatest shape change and the height of the alinotum grows quicker than its length, where a height/length ratio of 0.27 in minor workers and 0.32 in major workers is seen. [55] Due to this, larger workers tend to have a humped-shape and robust alinotum in contrast to smaller workers. No petiole segment exhibits any change in shape as the size of the body changes. The width of the gaster grows more rapidly than its length, where the width may be 96% of its length but increases to 106%. [55]

Physiology Edit

Like other insects, the red imported fire ant breathes through a system of gas-filled tubes called tracheae connected to the external environment through spiracles. The terminal tracheal branches (tracheoles) make direct contact with internal organs and tissue. The transport of oxygen to cells (and carbon dioxide out of cells) occurs through diffusion of gases between the tracheoles and the surrounding tissue and is assisted by a discontinuous gas exchange. [57] As with other insects, the direct communication between the tracheal system and tissues eliminates the need for a circulating fluid network to transport O2. [58] Thus, red imported fire ants and other arthropods can have a modest circulatory system though they have highly expensive metabolic demands. [59]

The excretory system consists of three regions. The basal region has three cells found within the posterior portion of the midgut. The anterior and superior cavities are formed by the bases of four Malpighian tubules. [60] The superior cavity opens into the lumen of the small intestine. The rectum is a large but thin-walled sac that occupies the posterior fifth of the larvae. The release of waste is controlled by the rectal valves that lead to the anus. [60] Sometimes, the larvae secrete a liquid that consists of uric acid, water and salts. [61] These contents are often carried outside by workers and ejected, but colonies under water stress may consume the contents. [60] In the reproductive system, queens release a pheromone that prevents dealation and oogenesis in virgin females those tested in colonies without a queen begin oocyte development after dealation and take up the egg-laying role. [62] Flight muscle degeneration is initiated by mating and juvenile hormones, and prevented by corpus allatectomy. [63] [64] Histolysis begins with the dissolution of the myofibril and the slow breakdown of the myofilaments. Such dissolution continues until it reaches the only free Z-line materials, which would also disappear only the nuclei and lamellar bodies remain. [60] In one study, the amino acids increase in the hemolymph after insemination. [65]

The glandular system contains four glands: the mandibular, maxillary, labial, and postpharyngeal glands. [60] The postpharyngeal is well developed in the queen, while the other glands are larger in workers. The postpharyngeal gland functions as a vacuum to absorb fatty acids and triglycerides, as well as a gastric caecum. [66] The functions of the other glands remain poorly understood. In one study discussing the enzymes of the digestion system of adult ants, lipase activity was found in the mandibular and labial glands, as well as invertase activity. The Dufour's gland found in the ant acts as a source of trail pheromones, although scientists believed the poison gland was the source of the queen pheromone. [60] [67] [68] The neurohormone pheromone biosynthesis activating neuropeptide is found in the ant that activates the biosynthesis of pheromones from the Dufour's gland. [69] The spermatheca gland is found in queens, which functions in sperm maintenance. Males appear to lack these glands, but those associated with its head are morphologically similar to those found in workers, but these glands may act differently. [66]

The ant faces many respiratory challenges due to its highly variable environment, which can cause increased desiccation, hypoxia, and hypercapnia. Hot, humid climates cause an increase in heart rate and respiration which increases energy and water loss. [58] [70] Hypoxia and hypercapnia can result from red imported fire ant colonies living in poorly ventilated thermoregulatory mounds and underground nests. Discontinuous gas exchange (DGE) may allow ants to survive the hypercapnic and hypoxic conditions frequently found in their burrows [57] it is ideal for adapting to these conditions because it allows the ants to increase the period of O2 intake and CO2 expulsion independently through spiracle manipulation. The invasion success of the red imported fire ant may possibly be related to its physiological tolerance to abiotic stress, being more heat tolerant and more adaptable to desiccation stress than S. richteri. This means that the ant is less vulnerable to heat and desiccation stress. Although S. richteri has higher water body content than the red imported fire ant, S. richteri was more vulnerable to desiccation stress. The lower sensitivity to desiccation is due to a lower water loss rate. [71] Colonies living in unshaded and warmer sites tend to have a higher heat tolerance than those living in shaded and cooler sites. [72]

Metabolic rate, which indirectly affects respiration, is also influenced by environmental temperature. Peak metabolism occurs at about 32 °C. [73] Metabolism, and therefore respiration rate, increases consistently as temperature increases. DGE stops above 25 °C, although the reason for this is currently unknown. [74]

Respiration rate also appears to be influenced significantly by caste. Males show a considerably higher rate of respiration than females and workers, due, in part, to their capability for flight and higher muscle mass. In general, males have more muscle and less fat, resulting in a higher metabolic O2 demand. [74] While the metabolic rate is highest at 32 °C, colonies often thrive at slightly cooler temperatures (around 25 °C). The high rate of metabolic activity associated with warmer temperatures is a limiting factor on colony growth because the need for food consumption is also increased. As a result, larger colonies tend to be found in cooler conditions because the metabolic demands required to sustain a colony are decreased. [73]

Red imported fire ants are native to the tropical areas of Central and South America, where they have an expansive geographical range that extends from southeastern Peru to central Argentina, and to the south of Brazil. [75] [76] [77] [78] In contrast to its geographical range in North America, its range in South America is significantly different. It has an extremely long north–south range, but a very narrow east–west distribution. The northernmost record of the red imported fire ant is Porto Velho in Brazil, and its southernmost record is Resistencia in Argentina this is a distance of about 3,000 km (1,900 mi). In comparison, the width of its narrow range is about 350 km (220 mi), and this is most likely narrower into southern Argentina and Paraguay and into the northern areas of the Amazon River basin. [79] Most known records of the red imported fire ant are around the Pantanal region of Brazil. However, the interior of this area has not been examined thoroughly, but it is certain that the species occurs in favourable locations around it. The Pantanal region is thought to be the original homeland of the red imported fire ant hydrochore dispersal via floating ant rafts could easily account for the far south populations around the Paraguay and Guaporé Rivers. The western extent of its range is not known exactly, but its abundance there may be limited. It may be extensive in easternmost Bolivia, owing to the presence of the Pantanal region. [79]

These ants are native to Argentina, and the red imported fire ant most likely came from here when they first invaded the United States in particular, populations of these ants have been found in the provinces of Chaco, Corrientes, Formosa, Santiago del Estero, Santa Fe, and Tucumán. [23] [79] [80] The northeastern regions of Argentina are the most credible guess where the invading ants originate. [77] In Brazil, they are found in northern Mato Grosso and in Rondônia and in São Paulo state. The red imported fire ant and S. saevissima are parapatric in Brazil, with contact zones known in Mato Grosso do Sul, Paraná state and São Paulo. [76] [81] In Paraguay they are found throughout the country, and have been recorded in Boquerón, Caaguazú, Canindeyú, Central, Guairá, Ñeembucú, Paraguarí, and Presidente Hayes departments Trager claims that the ant is distributed in all regions of the country. [82] [83] [84] They are also found in a large portion of northeastern Bolivia and, to a lesser extent, in northwestern Uruguay. [79] [85]

The red imported fire ant is able to dominate altered areas and live in a variety of habitats. It can survive the extreme weather of the South American rain forest, and in disturbed areas, nests are seen frequently alongside roads and buildings. [86] [87] The ant has been observed frequently around the floodplains of the Paraguay River. [88] In areas where water is present, they are commonly found around: irrigation channels, lakes, ponds, reservoirs, rivers, streams, riverbanks, and mangrove swamps. [82] [86] Nests are found in agricultural areas, coastlands, wetlands, coastal dune remnants, deserts, forests, grasslands, natural forests, oak woodland, mesic forest, leaf-litter, beach margins, shrublands, alongside rail and roads, and in urban areas. [89] In particular, they are found in cultivated land, managed forests and plantations, disturbed areas, intensive livestock production systems, and greenhouses. [86] [90] Red imported fire ants have been found to invade buildings, including medical facilities. [91] In urban areas, colonies dwell in open areas, especially if the area is sunny. [91] This includes: urban gardens, picnic areas, lawns, playgrounds, schoolyards, parks, and golf courses. [82] [91] In some areas, there are on average 200 mounds per acre. [92] During winter, colonies move under pavements or into buildings, and newly mated queens move into pastures. [86] [91] Red imported fire ants are mostly found at altitudes between 5 and 145 m (16 and 476 ft) above sea level. [82]

Mounds range from small to large, measuring 10 to 60 cm (3.9 to 23.6 in) in height and 46 cm (18 in) in diameter with no visible entrances. [86] [93] Workers are only able to access their nests thorugh a series of tunnels that protrude from the central region. Such protrusions can span up to 25 feet away from the central mound, either straight down in to the ground or, more commonly, sideways from the original mound. [94] Constructed from soil, mounds are oriented so that the long portions of the mound face toward the sun during the early morning and before sunset. [86] [93] Mounds are usually oval-shaped with the long axis of the nest orientating itself in a north–south direction. [95] These ants also spend large amounts of energy in nest construction and transporting brood, which is related with thermoregulation. The brood is transported to areas where temperatures are high workers track temperature patterns of the mound and do not rely on behavioural habits. [96] Inside nests, mounds contain a series of narrow horizontal tunnels, with subterranean shafts and nodes reaching grass roots 10 to 20 cm (3.9 to 7.9 in) below the surface these shafts and nodes connect the mound tunnels to the subterranean chambers. These chambers are about 5 cm 2 (0.77 inch 2 ) and reach depths of 10 to 80 cm (3.9 to 31.5 in). The mean number of ants in a single subterranean chamber is around 200. [97] [98] [99]

Introductions Edit

Red imported fire ants are among the worst invasive species in the world. [100] [101] Some scientists consider the red imported fire ant to be a "disturbance specialist" human disturbance to the environment may be a major factor behind the ants' impact (fire ants tend to favour disturbed areas). This is shown through one experiment, demonstrating that mowing and plowing in studied areas diminished the diversity and abundance of native ant species, whereas red imported fire ants found on undisturbed forest plots had only diminished a couple of species. [102] [103]

In the United States, the red imported fire ant first arrived in the seaport of Mobile, Alabama, by cargo ship between 1933 and 1945. [b] [c] [79] [106] [107] [108] Arriving with an estimated 9 to 20 unrelated queens, [109] [110] the red imported fire ant was only rare at the time, as entomologists were unable to collect any specimens (with the earliest observations first made in 1942, preceded by a population expansion in 1937) the population of these ants exploded by the 1950s. [111] [112] [113] Since its introduction to the United States, the red imported fire ant has spread throughout the southern states and northeastern Mexico, negatively affecting wildlife and causing economic damage. [75] [114] [115] [116] The expansion of red imported fire ants may be limited since they are almost wiped out during Tennessee winters, thus they may be reaching their northernmost range. [117] [118] [119] However, global warming may allow the red imported fire ant to expand its geographical range. [120] As of 2004, the ant is found in 13 states and occupies over 128 million hectares of land, and as many as 400 mounds can be found on a single acre of land. [121] [122] The United States Department of Agriculture estimates that they expand 120 miles (193 km) westward per year. [91] Likely due to absence of South American competitors - and lower numbers of native competitors - S. invicta dominates more extrafloral nectaries and hemipteran honeydew sources in the southern USA than in its home range. [123]

Red imported fire ants were first discovered in Queensland, Australia, in 2001. [124] [125] The ants were believed to be present in shipping containers arriving at the Port of Brisbane, most likely from North America. [126] Anecdotal evidence suggests fire ants may have been present in Australia for six to eight years prior to formal identification. The potential damage from the red imported fire ant prompted the Australian government to respond rapidly. A joint state and federal funding of A$175 million was granted for a six-year eradication programme. [127] [128] [129] Following years of eradication, eradication rates of greater than 99% from previously infested properties were reported. The program received extended Commonwealth funding of around A$10 million for at least another two years to treat the residual infestations found most recently. [130] In December 2014, a nest was identified at Port Botany, Sydney, in New South Wales. The port was quarantined, and a removal operation took place. [131] In September 2015, populations originating from the United States were found at a Brisbane airport. [132]

Red imported fire ants have spread beyond North America. The Invasive Species Specialist Group (ISSG) reports the ant inhabiting from three of the Cayman Islands. However, the sources the ISSG cited give no report about them on the island, but recent collections indicate that they are present. [75] In 2001, red imported fire ants were discovered in New Zealand, but they were successfully eradicated several years later. [75] [133] Red imported fire ants have been reported in India, [134] Malaysia, [135] the Philippines [136] and Singapore. [75] However, these reports were found to be incorrect as the ants collected there were incorrectly identified as the red imported fire ant. In Singapore, the ants were most likely misidentified as well. In India, surveyed ants in Sattur Taluk, India listed the red imported fire ant there in high populations meanwhile, no reports of the ant were made outside the surveyed area. In 2016, scientists state that despite no presence of the ant in India, the red imported fire ant will more than likely find suitable habitats within India's ecosystem if given the opportunity. [137] The reports in the Philippines most likely misidentified collected material as the red imported fire ant, as no populations have been found there. [75] It was discovered in Hong Kong and mainland China in 2004, where they have spread into several provinces as well as Macau and Taiwan. [138] [139] [140] [141] No geographic or climatic barriers prevent these ants from spreading further, thus it may spread throughout the tropical and subtropical regions of Asia. [121] [142] In Europe, a single nest was found in the Netherlands in 2002. [78]

Around 1980, red imported fire ants began spreading throughout the West Indies, where they were first reported in Puerto Rico and the U.S. Virgin Islands. [143] [144] Between 1991 and 2001, the ant was recorded from Trinidad and Tobago, several areas in the Bahamas, the British Virgin Islands, Antigua, and the Turks and Caicos Islands. [75] [145] [146] Since then, red imported fire ants have been recorded on more islands and regions, with new populations discovered in: Anguilla, Saint Martin, Barbuda, Montserrat, Saint Kitts, Nevis, Aruba, and Jamaica. [75] The ants recorded from Aruba and Jamaica have only been found on golf courses these courses import sod from Florida, so such importation may be an important way for the ant to spread throughout the West Indies. [75]

Populations found outside North America originate from the United States. In 2011, the DNA of specimens from Australia, China, and Taiwan was analysed with results showing that they are related to those in the United States. [147] Despite its spread, S. geminata has a greater geographical range than the red imported fire ant, but it can be easily displaced by it. Because of this, almost all of its exotic range in North America has been lost and the ant has almost disappeared there. On roadsides in Florida, 83% of these sites had S. geminata present when the red imported fire ant was absent, but only 7% when it is present. [75] This means that the ant can probably invade many tropical and subtropical regions where S. geminata populations are present. [75]

Red imported fire ants are extremely resilient and have adapted to contend with both flooding and drought conditions. If the ants sense increased water levels in their nests, they link together and form a ball or raft that floats, with the workers on the outside and the queen inside. [148] [149] [150] The brood is transported to the highest surface. [151] They are also used as the founding structure of the raft, except for the eggs and smaller larvae. Before submerging, the ants will tip themselves into the water and sever connections with the dry land. In some cases, workers may deliberately remove all males from the raft, resulting in the males drowning. The longevity of a raft can be as long as 12 days. Ants that are trapped underwater escape by lifting themselves to the surface using bubbles which are collected from submerged substrate. [151] Owing to their greater vulnerability to predators, red imported fire ants are significantly more aggressive when rafting. Workers tend to deliver higher doses of venom, which reduces the threat of other animals attacking. Due to this, and because a higher workforce of ants is available, rafts are potentially dangerous to those that encounter them. [152]

Necrophoric behaviour occurs in the red imported fire ant. Workers discard uneaten food and other such wastes away from the nest. The active component was not identified, but the fatty acids accumulating as a result of decomposition were implicated and bits of paper coated with synthetic oleic acid typically elicited a necrophoric response. The process behind this behaviour in imported red fire ants was confirmed by Blum (1970): unsaturated fats, such as oleic acid, elicit corpse-removal behaviour. [153] Workers also show differentiated responses towards dead workers and pupae. Dead workers are usually taken away from the nest, whereas the pupae may take a day for a necrophoric response to occur. Pupae infected by Metarhizium anisopliae are usually discarded by workers at a higher rate 47.5% of unaffected corpses are discarded within a day, but for affected corpses this figure is 73.8%. [154]

Red imported fire ants have negative impacts on seed germination. The extent of the damage, however, depends on how long seeds are vulnerable for (dry and germinating) and by the abundance of the ants. [155] One study showed that while these ants are attracted to and remove seeds which have adapted for ant dispersal, red imported fire ants damage these seeds or move them in unfavourable locations for germination. In seeds given to colonies, 80% of Sanguinaria canadensi seeds were scarified and 86% of Viola rotundifolia seeds were destroyed. [156] Small percentages of longleaf pine (Pinus palustris) seeds deposited by workers successfully germinate, thus providing evidence that red imported fire ants help the movement of seeds in the longleaf pine ecosystem. Elaiosome-bearing seeds are collected at a higher rate in contrast to nonelaiosome-bearing seeds and do not store them in their nests, but rather in surface trash piles in the mound vicinity. [157]

Foraging and communication Edit

Colonies of the red imported fire ant have tunneling surfaces that protrude out of the surfaces where workers forage. [158] [159] These areas of protrusion tend to be within their own territory, but greater ant colonisation can affect this. [160] Tunnels are designed to allow effective body, limb and antennae interactions with walls, and a worker can also move exceptionally fast inside them (more than nine bodylengths per second). [161] The holes exit out of any point within the colony's territory, and foraging workers may need to travel half a metre to reach the surface. Assuming the average forager travels 5 m, over 90% of foraging time is inside the tunnels during the day and rarely at night. Workers forage in soil temperatures reaching 27 °C (80 °F) and surface temperatures of 12–51 °C (53–123 °F). [159] Workers exposed to temperatures of 42 °C (107 °F) are at risk of dying from the heat. [159] The rate of workers foraging drops rapidly by autumn, and they rarely emerge during winter. This may be due to the effects of soil temperature, and a decreased preference for food sources. These preferences only decrease when brood production is low. In the northern regions of the United States, areas are too cold for the ant to forage, but in other areas such as Florida and Texas, foraging may occur all year round. When it is raining, workers do not forage outside, as exit holes are temporarily blocked, pheromone trails are washed away, and foragers may be physically struck by the rain. The soil's moisture may also affect the foraging behaviour of workers. [159]

When workers are foraging, it is characterised by three steps: searching, recruitment, and transportation. [162] Workers tend to search for honey more often than other food sources, and the weight of food has no impact on searching time. Workers may recruit other nestmates if the food they have found is too heavy, taking as much as 30 minutes for the maximum number of recruited workers to arrive. Lighter food sources take less time and are usually transported rapidly. [162] Foraging workers become scouts and search solely for food outside the surface, and may subsequently die two weeks later from old age. [163]

Workers communicate by a series of semiochemicals and pheromones. These communication methods are used in a variety of activities, such as nestmate recruitment, foraging, attraction, and defence for example, a worker may secrete trail pheromones if a food source it discovered is too large to carry. [164] These pheromones are synthesized by the Dufour's gland and may trail from the discovered food source back to the nest. [165] [166] The components in these trail pheromones are also species-specific to this ant only, in contrast to other ants with common tail pheromones. [167] The poison sack in this species has been identified as being the novel storage site of the queen pheromone this pheromone is known to elicit orientation in worker individuals, resulting in the deposition of brood. [68] [168] It is also an attractant, where workers aggregate toward areas where the pheromone has been released. [164] A brood pheromone is possibly present, as workers are able to segregate brood by their age and caste, which is followed by licking, grooming and antennation. [164] If a colony is under attack, workers will release alarm pheromones. [169] However, these pheromones are poorly developed in workers. Workers can detect pyrazines which are produced by the alates these pyrazines may be involved in nuptial flight, as well as an alarm response. [170]

Red imported fire ants can distinguish nestmates and non-nestmates through chemical communication and specific colony odours. [164] [171] Workers prefer to dig into nest materials from their own colony and not from soil in unnested areas or from other red imported fire ant colonies. One study suggests that as a colony's diet is similar, the only difference between nested and unnested soil was the nesting of the ants themselves. Therefore, workers may transfer colony odour within the soil. [171] Colony odour can be affected by the environment, as workers in lab-reared colonies are less aggressive than those in the wild. [172] Queen-derived cues are able to regulate nestmate recognition in workers and amine levels. However, these cues do not play a major role in colony-level recognition, but they can serve as a form of caste-recognition within nests. [173] [174] Workers living in monogyne societies tend to be extremely aggressive and attack intruders from neighbouring nests. In queenless colonies, the addition of alien queens or workers does not increase aggression among the population. [175]

Diet Edit

Red imported fire ants are omnivores, and foragers are considered to be scavengers rather than predators. [176] The ants' diet consists of dead mammals, arthropods, [177] insects, earthworms, vertebrates, and solid food matter such as seeds. However, this species prefers liquid over solid food. The liquid food the ants collect is sweet substances from plants or honeydew-producing hemipterans. [93] [176] [178] [179] Arthropod prey may include dipteran adults, larvae and pupae, and termites. The consumption of sugar amino acid is known to affect recruitment of workers to plant nectars. Mimic plants with sugar rarely have workers to feed on them, whereas those with sugar and amino acids have considerable numbers. [180] [181] The habitats where they live may determine the food they collect the most for example, forage success rates for solid foods are highest in lakeshore sites, while high levels of liquid sources were collected from pasture sites. [182] Specific diets can also alter the growth of a colony, with laboratory colonies showing high growth if fed honey-water. Colonies that feed on insects and sugar-water can grow exceptionally large in a short period of time, whereas those that do not feed on sugar-water grow substantially slower. Colonies that do not feed on insects cease brood production entirely. [179] Altogether, the volume of food digested by nestmates is regulated within colonies. [183] Larvae are able to display independent appetites for sources such as solid proteins, amino acid solutions, and sucrose solutions, and they also prefer these sources over dilute solutions. Such behaviour is due to their capability to communicate hunger to workers. The rate of consumption depends on the type, concentration, and state of the food on which they feed. Workers tend to recruit more nestmates to food sources filled with high levels of sucrose than to protein. [183]

Food distribution plays an important role in a colony. This behaviour varies in colonies, with small workers receiving more food than larger workers if a small colony is seriously deprived of food. In larger colonies, however, the larger workers receive more food. Workers can donate sugar water efficiently to other nestmates, with some acting as donors. These "donors" distribute their food sources to recipients, which may also act as donors. Workers may also share a greater portion of their food with other nestmates. [184] In colonies that are not going through starvation, food is still distributed among the workers and larvae. One study shows that honey and soybean oil were fed to the larvae after 12 to 24 hours of being retained by the workers. The ratio distribution of these food sources was 40% towards the larvae and 60% towards the worker for honey, and for soybean oil this figure was around 30 and 70%, respectively. [185] Red imported fire ants also stockpile specific food sources such as insect pieces rather than consuming them immediately. These pieces are usually transported below the mound surface and in the driest and warmest locations. [186]

This species engages in trophallaxis with the larvae. [187] Regardless of the attributes and conditions of each larva, they are fed roughly the same amount of liquid food. The rate of trophallaxis may increase with larval food deprivation, but such increase depends on the size of each larva. Larvae that are fed regularly tend to be given small amounts. To reach satiation, all larvae regardless of their size generally require the equivalent of eight hours of feeding. [188]

Predators Edit

A number of insects, arachnids, and birds prey on these ants, especially when queens are trying to establish a new colony. [189] While in the absence of defending workers, the fire ant queens must rely on their venom to keep off competitor species [2] Many species of dragonfly, including Anax junius, Pachydiplax longipennis, Somatochlora provocans, and Tramea carolina, capture the queens while they are in flight 16 species of spiders, including the wolf spider Lycosa timuga and the southern black widow spider (Latrodectus mactans), actively kill red imported fire ants. L. mactans captures all castes of the species (the workers, queens, and males) within its web. These ants constitute 75% of prey captured by the spider. Juvenile L. mactans spiders have also been seen capturing the ants. [189] [190] Other invertebrates that prey on red imported fire ants are earwigs (Labidura riparia) and tiger beetles (Cicindela punctulata). [189] Birds that eat these ants include the chimney swift (Chaetura pelagica), the eastern kingbird (Tyrannus tyrannus), and the eastern bobwhite (Colinus virginianus virginianus). The eastern bobwhite attacks these ants by digging out the mounds looking for young queens. [189] Red imported fire ants have been found in stomach contents inside of armadillos. [191]

Many species of ants have been observed attacking queens and killing them. Apparently, the venom of fire ant queens is chemically adapted to rapidly subdue offending competitor ants. [2] Predatory ants include: Ectatomma edentatum, Ephebomyrmex spp., Lasius neoniger, Pheidole spp., Pogonomyrmex badius, and Conomyrma insana, which is among the most significant. [189] [192] [193] C. insana ants are known to be effective predators against founding queens in studied areas of Northern Florida. The pressure of attacks initiated by C. insana increase over time, causing queens to exhibit different reactions, including escaping, concealment, or defence. Most queens that are attacked by these ants are ultimately killed. [192] Queens that are in groups have higher chances of survival than solitary queens if they are attacked by S. geminata. [194] Ants can attack queens on the ground and invade nests by stinging and dismembering them. Other ants such as P. porcula try to take the head and gaster, and C. clara invade in groups. Also, certain ants try to drag queens out of their nests by pulling on the antennae or legs. [193] Small, monomorphic ants rely on recruitment to kill queens and do not attack them until reinforcements arrive. Aside from killing the queen, some ants may steal the eggs for consumption or emit a repellent that is effective against red imported fire ants. [193] Certain ant species may raid colonies and destroy them. [195]

Parasites, pathogens and viruses Edit

Flies in the genus Pseudacteon (phorid flies) are known to be parasitic to ants. Some species within this genus, such as Pseudacteon tricuspis, have been introduced into the environment for the purpose of controlling the imported fire ant. These flies are parasitoids of the red imported fire ant in its native range in South America, and can be attracted through the ants' venom alkaloids. [196] One species, Pseudacteon obtusus, attacks the ant by landing on the posterioral portion of the head and laying an egg. The location of the egg makes it impossible for the ant to successfully remove it. [197] The larvae migrate to the head, then develop by feeding on the hemolymph, muscle tissue, and nervous tissue. After about two weeks, they cause the ant's head to fall off by releasing an enzyme that dissolves the membrane attaching the head to its body. The fly pupates in the detached head capsule, emerging two weeks later. [197] [198] P. tricuspis is another phorid fly that is a parasitoid to this species. Although parasitism pressures by these flies do not affect the ants' population density and activity, it has a small effect on a colony population. [199] The strepsipteran insect Caenocholax fenyesi is known to infect male ants of this species and attack the eggs, [200] [201] and the mite Pyemotes tritici has been considered a potential biological agent against red imported fire ants, capable of parasitising every caste within the colony. [202] Bacteria, such as Wolbachia, has been found in the red imported fire ant three different variants of the bacteria are known to infect the red imported fire ant. However, its effect on the ant is unknown. [203] [204] Solenopsis daguerrei is a reproductive parasite to red imported fire ant colonies. [205]

A large variety of pathogens and nematodes also infect red imported fire ants. Pathogens include Myrmecomyces annellisae, Mattesia spp., Steinernema spp., [206] a mermithid nematode, [207] Vairimorpha invictae, which can be transmitted via live larvae and pupae and dead adults [208] [209] and Tetradonema solenopsis, which can be fatal to a large portion of a colony. [210] Individuals infected by Metarhizium anisopliae tend to perform trophallaxis more frequently and have an enhanced preference to quinine, an alkaloid substance. [211] Phorid flies with Kneallhazia solenopsae can serve as vectors in transmitting the disease to the ants. [212] Weakening the colony, infections from this disease are localised within the body fat, with spores only occurring in adult individuals. [213] [214] The mortality of an infected colony tends to be greater in contrast to those that are healthy. [207] These ants are a host to Conidiobolus, [215] Myrmicinosporidium durum, and Beauveria bassiana, each of which are parasitic fungi. Infected individuals have spores all over their bodies and appear darker than usual. [216] [217] [218] The toxicity from antimicrobial property of volatiles produced by the ants can significantly reduce the germination rate of B. bassiana within the colony. [219]

A virus, S. invicta 1 (SINV-1), has been found in about 20% of fire ant fields, where it appears to cause the slow death of infected colonies. It has proven to be self-sustaining and transmissible. Once introduced, it can eliminate a colony within three months. Researchers believe the virus has potential as a viable biopesticide to control fire ants. [220] [221] [222] Two more viruses have also been discovered: S. invicta 2 (SINV-2) and S. invicta 3 (SINV-3). Polygynous colonies tend to face greater infections in contrast to monogynous colonies. Multiple virus infections can also occur. [223] [224]

Lifecycle and reproduction Edit

Nuptial flight in red imported fire ants begins during the warmer seasons of the year (spring and summer), usually two days after rain. The time alates emerge and mate is between noon and 3:00 pm. [225] [226] Nuptial flights recorded in North Florida have, on average, 690 female and male alates participating in a single flight. [227] Males are the first to leave the nest, and both sexes readily undertake flight with little to no preflight activity. However, workers swarm the mound excitedly stimulated by mandibular glands within the head of the alates. [228] [229] As mounds do not have holes, workers form holes during nuptial flight as a way for the alates to emerge. This behaviour in workers, elicited by the pheromones, includes rapid running and back-and-forth movements, and increased aggression. Workers also cluster themselves around the alates as they climb up on vegetation, and in some cases, attempt to pull them back down before they take flight. Chemical cues from males and females during nuptial flight attract workers, but chemical cues released by workers do not attract other nestmates. It also induces alarm-recruitment behaviour in workers which results in a higher rate of alate retrieval. [228] [230]

Males fly at higher elevations than females: captured males are usually 100 to 300 m (330 to 980 ft) above the surface, whereas the females are only 60 to 120 m (200 to 390 ft) above the surface. A nuptial flight takes place for roughly half an hour and females generally fly for less than 1.6 km (0.99 mi) before landing. About 95% of queens successfully mate and only mate once some males may be infertile due to the testicular lobes failing to develop. [225] [231] [232] [233] [234] [235] In polygyne colonies, males do not play a significant role and most are, therefore, sterile one of the reasons for this is to avoid mating with other ant species. This also makes male mortality selective, which may affect the breeding system, mating success and, gene flow. [236] [237] Ideal conditions for a nuptial flight to begin is when humidity levels are above 80% and when the soil temperature is above 18 °C (64 °F). Nuptial flights only occur when the ambient temperature is 24–32 °C (75–89 °F). [225]

Queens are often found 1–2.3 miles from the nest they flew from. Colony founding can be done by an individual or in groups, known as pleometrosis. [238] This joint effort of the co-foundresses contributes to the growth and survival of the incipient colony nests founded by multiple queens begin the growth period with three times as many workers when compared to colonies founded by a single queen. Despite this, such associations are not always stable. [239] [240] [241] [242] The emergence of the first workers instigates queen-queen and queen-worker fighting. In pleometrotic conditions, only one queen emerges victorious, whereas the queens that lost are subsequently killed by the workers. [243] The two factors that could affect the survival of individual queens are their relative fighting capabilities and their relative contribution to worker production. Size, an indicator of fighting capacity, positively correlates with survival rates. However, manipulation of the queen's relative contribution to worker production had no correlation with survival rate. [244]

A single queen lays around 10 to 15 eggs 24 hours after mating. [93] In established nests, a queen applies venom onto each egg that perhaps contains a signal calling for workers to move it. [245] These eggs remain unchanged in size for one week until they hatch into larvae. By this time, the queen will have laid about 75 to 125 more eggs. The larvae that hatch from their eggs are usually covered in their shell membranes for several days. The larvae can free their mouthparts from their shells using body movements, but still need assistance from workers with hatching. The larval stage is divided into four instars, as observed through the moulting stages. At the end of each moult, a piece of unknown material is seen connected to the exuviae if they are isolated from the workers. The larval stage lasts between six and 12 days before their bodies expand significantly and become pupae the pupal stage lasts between nine and 16 days. [44] [93]

As soon as the first individuals reach the pupal stage, the queen ceases egg production until the first workers mature. This process takes two weeks to one month. The young larvae are fed oils which are regurgitated from her crop, as well as trophic eggs or secretions. She also feeds the young her wing muscles, providing the young with needed nutrients. The first generation of workers are always small because of the limit of nutrients needed for development. These workers are known as minims or nanitics, which burrow out of the queen's chamber and commence foraging for food needed for the colony. Mound construction also occurs at this time. Within a month after the first generation is born, larger workers (major workers) start to develop, and within six months, the mound will be noticeable, if viewed, and houses several thousand residents. A mature queen is capable of laying 1,500 eggs per day all workers are sterile, so cannot reproduce. [93] [246] [247] [248]

A colony can grow exceptionally fast. Colonies that housed 15–20 workers in May grew to over 7,000 by September. These colonies started to produce reproductive ants when they were a year old, and by the time they were two years old, they had over 25,000 workers. The population doubled to 50,000 when these colonies were three years old. [249] At maturity, a colony can house 100,000 to 250,000 individuals, but other reports suggest that colonies can hold more than 400,000. [d] [250] [251] [252] [253] Polygyne colonies have the potential to grow much larger than monogyne colonies. [251]

Several factors contribute to colony growth. Temperature plays a major role in colony growth and development colony growth ceases below 24 °C and developmental time decreases from 55 days at temperatures of 24 °C to 23 days at 35 °C. Growth in established colonies only occurs at temperatures between 24 and 36 °C. Nanitic brood also develops far quicker than minor worker brood (around 35% faster), which is beneficial for founding colonies. [254] Colonies that have access to an unlimited amount of insect prey are known to grow substantially, but this growth is further accelerated if they are able to access plant resources colonised by hemipteran insects. [255] In incipient monogyne colonies where diploid males are produced, colony mortality rates are significantly high and colony growth is slow. In some cases, monogyne colonies experience 100% mortality rates in the early stages of development. [256]

The life expectancy of a worker ant depends on its size, although the overall average is around 62 days. [257] Minor workers are expected to live for about 30 to 60 days, whereas the larger workers live much longer. Larger workers, which have a life expectancy of 60 to 180 days, live 50–140% longer than their smaller counterparts, but this depends on the temperature. [93] [258] However, workers kept in laboratory conditions have been known to live for 10 to 70 weeks (70 days to 490 days) the maximum recorded longevity of a worker is 97 weeks (or 679 days). [259] The queens live much longer than the workers, with a lifespan ranging from two years to nearly seven years. [93] [259]

In colonies, queens are the only ants able to alter sex ratios which can be predicted. For example, queens originating from male-producing colonies tend to produce predominantly males, while queens that came from female-favoured sex ratio colonies tend to produce females. [260] [261] Queens also exert control over the production of sexuals through pheromones that influence the behaviours of workers toward both male and female larvae. [262]

Monogyny and polygyny Edit

There are two forms of society in the red imported fire ant: polygynous colonies and monogynous colonies. [263] [264] [263] Polygynous colonies differ substantially from monogynous colonies in social insects. The former experience reductions in queen fecundity, dispersal, longevity, and nestmate relatedness. [265] [266] [267] [268] Polygynous queens are also less physogastric than monogynous queens and workers are smaller. [269] [270] Understanding the mechanisms behind queen recruitment is integral to understanding how these differences in fitness are formed. It is unusual that the number of older queens in a colony does not influence new queen recruitment. Levels of queen pheromone, which appears to be related to queen number, play important roles in the regulation of reproduction. It would follow that workers would reject new queens when exposed to large quantities of this queen pheromone. Moreover, evidence supports the claim that queens in both populations enter nests at random, without any regard for the number of older queens present. [271] There is no correlation between the number of older queens and the number of newly recruited queens. Three hypotheses have been posited to explain the acceptance of multiple queens into established colonies: mutualism, kin selection, and parasitism. [272] The mutualism hypothesis states that cooperation leads to an increase in the personal fitness of older queens. However, this hypothesis is not consistent with the fact that increasing queen number decreases both queen production and queen longevity. [273] Kin selection also seems unlikely given that queens have been observed to cooperate under circumstances where they are statistically unrelated. [274] Therefore, queens experience no gain in personal fitness by allowing new queens into the colony. Parasitism of preexisting nests appears to be the best explanation of polygyny. One theory is that so many queens attempt to enter the colony that the workers get confused and inadvertently allow several queens to join it. [274]

Monogyne workers kill foreign queens and aggressively defend their territory. However, not all behaviours are universal, primarily because worker behaviours depend on the ecological context in which they develop, and the manipulation of worker genotypes can elicit change in behaviours. Therefore, behaviours of native populations can differ from those of introduced populations. [275] In a study to assess the aggressive behaviour of monogyne and polygyne red fire ant workers by studying interaction in neutral arenas, and to develop a reliable ethogram for readily distinguishing between monogyne and polygyne colonies of red imported fire ants in the field, [276] monogyne and polygyne workers discriminated between nestmates and foreigners as indicated by different behaviours ranging from tolerance to aggression. Monogyne ants always attacked foreign ants independently if they were from monogyne or polygyne colonies, whereas polygyne ants recognised, but did not attack, foreign polygyne ants, mainly by exhibiting postures similar to behaviours assumed after attacks by Pseudacteon phorids. Hostile versus warning behaviours were strongly dependent on the social structure of workers. Therefore, the behaviour toward foreign workers was a method of characterising monogyne and polygyne colonies. [277] Most colonies in the southeastern and south-central US tend to be monogynous. [242]

The monogynous red imported fire ant colony territorial area and the mound size are positively correlated, which, in turn, is regulated by the colony size (number and biomass of workers), distance from neighbouring colonies, prey density, and by the colony's collective competitive ability. In contrast, nestmate discrimination among polygynous colonies is more relaxed as workers tolerate conspecific ants alien to the colony, accept other heterozygote queens, and do not aggressively protect their territory from polygyne conspecifics. [278] These colonies might increase their reproductive output as a result of having many queens and the possibility of exploiting greater territories by means of cooperative recruitment and interconnected mounds. [279]

A social chromosome is present in the red imported fire ant. This chromosome can differentiate the social organisation of a colony carrying one of two variants of a supergene (B and b) which contains more than 600 genes. The social chromosome has often been compared to sexual chromosomes because they share similar genetic features [280] and they define colony phenotype in a similar way. For example, colonies exclusively carrying the B variant of this chromosome accept single BB queens, but colonies with both B and b variants will accept multiple Bb queens only. [281] Differences in another single gene can also determine whether the colony will have single or multiple queens. [282]

Relationship with other organisms Edit

When polygyne forms invade areas where colonies have not yet been established, the diversity of native arthropods and vertebrates declines greatly. [283] This is evident as populations of isopods, mites and tumblebug scarabs decline significantly. They can also significantly alter the populations of many fly and beetle families, including: Calliphoridae, Histeridae, Muscidae, Sarcophagidae, Silphidae, and Staphylinidae. Despite this, one review found that certain insects may be unaffected by red imported fire ants for example, the density of isopods decreases in red imported fire ant infested areas, but crickets of the genus Gryllus are unaffected. There are some cases where the diversity of certain insect and arthropod species increase in areas where red imported fire ants are present. [284] [285] [286] Red imported fire ants are important predators on cave invertebrates, some of which are endangered species. This includes harvestmen, pseudoscorpions, spiders, ground beetles, and pselaphid beetles. The biggest concern is not the ant itself, but the bait used to treat them because this can prove fatal. Stock Island tree snails (Orthalicus reses) are extinct in the wild predation by red imported fire ants is believed to be the major factor in the snail's extinction. [284] Overall, red imported fire ants prefer specific arthropods to others, although they attack and kill any invertebrate that cannot defend itself or escape. [287] Arthropod biodiversity increases once red imported fire ant populations are either reduced or eradicated. [114] [288]

Interactions between red imported fire ants and mammals have been rarely documented. However, deaths of live-trapped animals by red imported fire ants have been observed. [284] [289] [290] Mortality rates in eastern cottontail (Sylvilagus floridanus) young range from 33 to 75% because of red imported fire ants. [291] It is believed that red imported fire ants have a strong impact on many herpetofauna species scientists have noted population declines in the Florida kingsnake (Lampropeltis getula floridana), and eggs and adults of the eastern fence lizard (Sceloporus undulatus) and six-lined racerunner (Aspidoscelis sexlineata) are a source of food. [292] [293] [294] Because of this, eastern fence lizards have adapted to have longer legs and new behaviours to escape the red imported fire ant. [295] [296] Adult three-toed box turtles (Terrapene carolina triunguis), Houston toad (Anaxyrus houstonensis) juveniles, and American alligator (Alligator mississippiensis) hatchlings are also attacked and killed by these ants. [284] [297] [298] [299] Despite this mostly-negative association, one study shows that red imported fire ants may be capable of impacting vector-borne disease transmissions by regulating tick populations and altering vector and host dynamics, thereby reducing transmission rates not only to animals, but to humans as well. [300]

Mortality rates have been well observed in birds there have been instances where no young have survived to adulthood in areas with high fire ant density. Many birds including cliff nesting swallows, ducks, egrets, quail, and terns have been affected by red imported fire ants. [301] Ground nesting birds, particularly the least tern (Sterna antillarum), are vulnerable to fire ant attacks. [302] [299] The impact of red imported fire ants on colonial breeding birds is especially severe waterbirds can experience a mortality rate of 100%, although this factor was lower for early-nesting birds. Brood survival decreases in American cliff swallows (Petrochelidon pyrrhonota) if they are exposed to foraging workers. [303] Songbird nest survival decreases in areas with red imported fire ants present, but survival rates in white-eyed vireo (Vireo griseus) and black-capped vireo (Vireo atricapilla) nests increase from 10% to 31% and 7% to 13% whenever fire ants are not present or when they are unable to attack them. [304] Red imported fire ants may indirectly contribute to low brood survival in the Attwater's prairie chicken. [305] It was first thought that the ants were linked to the decline of overwintering birds such as the loggerhead shrike (Lanius ludovicianus), but a later study showed that ant eradication efforts using the pesticide Mirex, which was known to have toxic side effects, was largely to blame. [306] [307]

Red imported fire ants are strong competitors with many ant species. They have managed to displace many native ants which has led to a number of ecological consequences. [308] However, studies show that these ants are not always superior competitors that suppress native ants. Habitat disturbance prior to their arrival, and recruitment limitations, are more plausible reasons why native ants are suppressed. [309] Between Tapinoma melanocephalum and Pheidole fervida, the red imported fire ant is stronger than both species but shows different levels of aggression. For example, they are less hostile towards T. melanocephalum in contrast to P. fervida. Mortality rates in T. melanocephalum and P. fervida when fighting with red imported fire ants are high, being 31.8% and 49.9% respectively. The mortality rate for red imported fire ant workers, however, is only 0.2% to 12%. [310] The imported crazy ant (Nylanderia fulva) exhibits greater dominance than the red imported fire ant and has been known to displace them in habitats where they encounter each other in. [311] Larger colonies of pavement ants (Tetramorium caespitum) can destroy red imported fire ant colonies, leading entomologists to conclude that this conflict between the two species may help impede the spread of the red imported fire ant. [312] [313] Individuals infected by SINV-1 can be killed faster than healthy individuals by Monomorium chinense. This means that ants infected with SINV-1 are weaker than their healthy counterparts and more than likely will be eliminated by M. chinense. However, major workers, whether they are infected or not, are rarely killed. [314]

In areas it is native to, the red imported fire ant is still a dominant species and coexists with 28 ant species in gallery forest gaps and ten species in xerophytic forest grassland, winning most aggressive interactions with other ants. However, some ants can be co-dominant in areas where they coexist such as the Argentine ant, where they compete symmetrically. [315] [316] Workers regularly engage in food competition with other ants, and can suppress the exploitation of food resources from honeydew-producing hemipterans (specifically from Phenacoccus solenopsis) from native ants however, red imported fire ants are unable to eliminate T. melanocephalum completely although they consume a higher proportion of food. Instead, the two ants may peacefully coexist and share the honeydew. [317] [318] When encountering neighboring fire ants, workers may take on death-feigning behaviours to avoid them with success. However, such behaviour is only seen in young workers, as older workers either flee or fight back when threatened. [319]

As mentioned, red imported fire ants and Argentine ants compete with each other. Mortality rates vary in different scenarios (i.e. mortality rates in colony confrontation is lower than those confronting each other in the field). Major workers can also withstand more injuries to their bodies, thus increasing the mortality rate of Argentine ants. For an Argentine ant colony to successfully wipe out a monogyne colony of 160,000 workers, the colony would need 396,800 workers. A colony that has reduced in size due to successful bait treatment are prone to predation by Argentine ants. The ants may play a vital role in removing weakened fire ant colonies, and they may also be important in slowing the spread of these fire ants, especially in heavily infested Argentine ant areas. [320] Despite this, Argentine ant populations in the southeastern United States have declined following the introduction of the red imported fire ant. [321]

Red imported fire ants have formed a relationship with an invasive mealybug, Phenacoccus solenopsis. Colony growth is known to increase if ants have access to resources produced by P. solenopsis, and the population density of these mealybugs is significantly higher in areas where red imported fire ants are present (the spread of P. solenopsis in areas it is not native is attributed to the presence of the ants). As well as that, the life expectancy and reproductive rate of P. solenopsis both increase. These mealybugs may even be transported by workers back to their nest. [322] Predation of P. solenopsis decreases due to tending workers interfering with the predation and parasitism by natural enemies. Mealybugs are preyed on by the lady beetle (Menochilus sexmaculatus) and are hosts of two parasites (Aenasius bambawalei and Acerophagus coccois) if there are no ants present, but this is different if ants are present. Lady beetles are less frequently seen on plants with red imported fire ants, and the rate of "mummy" nymphs is significantly lower. [322] This is clearly evident as scientists observed that cotton aphid (Aphis gossypii) populations, and the predation of sentinel bollworm eggs, increased in areas with red imported fire ant presence. [323] [324] [325] Red imported fire ants have developed a mutual relationship with another mealybug (Dysmicoccus morrisoni). The ants promote the colony growth of D. morrisoni through protection, covering the colonies up with debris and collecting the honeydew they secrete. [326]

The toxicology of red imported fire ant venom has been relatively well studied. The venom is important to the ant, enabling it to capture its prey and to defend itself. Some 14 million people are stung annually in the United States, [327] who may suffer reactions ranging from mild eczema to anaphylactic shock. [328] Most common reactions to fire ant stings are a burning sensation at the sting site, followed by urticaria and pustule formation. [329] Some victims may develop a more serious allergic reaction which can be life-threatening. [330] [331] The venom is mainly composed of insoluble alkaloids with a minor watery phase [332] containing some 46 proteins [333] of which four are reported as allergens. [334] [335] Effective immunotherapy is available. [336]

As pests Edit

Because of their notoriety and invasive behaviour, red imported fire ants are considered pests. In the United States, the Food and Drug Administration estimates more than $5 billion is spent annually on medical treatment, damage, and control in infested areas. [337] [338] In Texas alone, red imported fire ants caused $300 million in damages for livestock, wildlife and public health. [339] Approximately $36 per American household, and more than $250 million has been spent to control and eradicate red imported fire ants. Private agencies spend $25 to $40 million on pesticides annually. [93] Unsuccessful eradication in Australia may cost the economy billions in damages annually and, based on a Queensland government study, the estimated cost could reach $43 billion over 30 years. [340]

Red imported fire ants thrive in urban areas, especially in backyards, golf courses, parks, recreational areas, school grounds, and street verges, in which their presence may deter outdoor activities. If they enter homes or properties, they can harm pets if they are caged, penned, tied or cannot escape. [338] [341] Nests can be built under pavements or even roads, as well as under driveways, foundations, lawns, edges of sidewalks, under patio slabs, in electrical boxes or near power lines. A colony can excavate huge quantities of soil, resulting in structural problems in driveways, pavings and walls, and can also cause the formation of potholes in roads. [93] [338] [342] [343] [344] Additional damage by mounds can be inflicted on trees, yard plants, and pipes some structures may also collapse. Colonies may migrate into human homes after heavy rain to take refuge from saturated soil. [47] [93]

Not only do they thrive in urban areas, red imported fire ants can damage equipment and infrastructure and impact business, land, and property values. [341] They are also attracted to electricity electrically stimulated workers release venom alkaloids, alarm pheromones, and recruitment pheromones, which in return attracts more workers to the site. [345] As a result, red imported fire ants can destroy electrical equipment. [346] This is known as magnetism, where scientists have identified internal magnetic materials which may play a role in orientation behaviours. [347] [348] They are known to chew through electrical insulation which causes damage to electric motors, irrigation lines, pumps, signal boxes, transformers, telephone exchanges, and other equipment. [338] [349] Colonies aggregate near electrical fields and are capable of causing short circuits or interfering with switches and equipment such as air conditioners, computers, and water pumps. They are also known to infest airport landing areas and traffic lights. [349]

In agriculture Edit

The red imported fire ant is a significant agricultural pest in areas where it is not native. They are capable of damaging crops, and they threaten pastures and orchards. [341] The mounds themselves can destroy agricultural equipment such as irrigation systems and damage machinery during harvest time. [350] The ants are known to invade soybean crops causing lower yields, and could cause $156 million in losses for soybean crops in the southeastern United States. [93] [351] [352] Reports from Georgia and North Carolina claim that 16.8 to 49.1 kg/ha of soybeans could not be harvested due to interference from fire ant mounds combine harvesters skipped over the mounds preventing the crops from being harvested, and farmers raised the cutter bars on their combine harvesters to avoid impacting the mounds. [353] [354] [355] The feeding behaviour of red imported fire ants can result in significant damage to many other crops, including: beans, cabbage, citrus, corn, cucumber, eggplant, okra, peanut, potato, sorghum, sunflower, and sweet potato. The ants also interfere with plants' root systems and feed on young growth. [93] [356] Sometimes, colonies build mounds around or near the base of citrus trees chew off new growth and feed on the flowers or developing fruit. Citrus trees are often girdled or killed. [357]

Despite its pest status and notoriety, the red imported fire ant can be beneficial. The ant is an effective insect predator, so it may serve as a biological agent against other pest species, especially in sugarcane fields. [358] Pest insects the ant kills include: boll weevils (Anthonomus grandis) in cotton crops, [359] [360] [361] sugarcane borers (Diatraea saccharalis) in sugarcane fields, [362] [363] [364] horn flies (Haematobia irritans) in manure, [365] velvetbean caterpillars (Anticarsia gemmatalis) in soybeans, and whiteflies that are found in greenhouses. [366] [367] A number of studies indicate that red imported fire ants do not interfere or attack insects of economic importance in cotton fields, which has resulted in many farmers in the southeastern regions of the United States viewing red imported fire ants as beneficial. [368] However, some scientists have suggested that the beneficial status of the red imported fire ant is hard to predict when geography, plant size, season, soil moisture and the use of insecticides are not considered. These factors may lower the efficacy of red imported fire ants as pest control agents. Another factor is that workers are indiscriminate and kill beneficial insects such as predators that eat horn flies and other pests in pastures and predators of aphids and scale insects. [368] [369] [370] They also reduce the efficacy of parasitic wasps against pest species by eating the larvae and pupae. [368] [371]

Control Edit

In comparison to other ant species like Anoplolepis gracilipes, which rapidly take over areas they have been contained in, red imported fire ants are fairly easy to control. [372] The first proposals to controlling the ant occurred in 1957 when the United States Congress authorised an eradication program using federal and state funding. Research on the ant and its biology has been continuous after the establishment of an eradication program, and many chemicals were used to eliminate them. However, scientists discovered that these insecticides were killing native fauna, and the Environmental Protection Agency subsequently outlawed them. Some scientists even questioned whether the ants were pests or not. [373] [374] Today, it is unlikely that the red imported fire ant will be eradicated in areas such as the United States. Populations can be managed properly if an integrated approach is used. [375] Some scientists have considered using the ants' natural enemies against it this includes Kneallhazia solenopsae and B. bassiana. Phorid flies have also been viewed as potential biological agents, as they can reduce foraging activity in red imported fire ants and affect population levels. However, they are unable to affect colony growth rate. [376] In addition, parasitic ants, parasitic wasps, mites, other pathogens, nematodes, and fungi have been considered to be potential biological agents. [377] Others suggest that populations can be maintained or reduced by manipulating several ecological factors. [378]

Several baits have been used to control populations. Mounds are destroyed in a matter of weeks if baits are used on them. Baits are considered to be effective and simple to use against red imported fire ants, in comparison to drenching, dusting, or fumigating. They are sprinkled onto the mound then the ants take and consume them. [379] [380] Certain baits such as growth regulator baits, and boric acid-sucrose water baits, benefit native fauna and low concentrations are usually required to kill a colony. [381] [382] Others baits used against red imported fire ants include Amdro, Ascend, hydramethylnon, and Maxforce. [383]

Solid and liquid bait insecticides, if improperly applied in a location, may be moved through waterflow in to unintended water sources. Often, this happens through non-point sources including many diffuse sources. As snow melts and rainfall moves over and through the ground, the water picks up improperly applied insecticides and deposits them in to larger bodies of water, rivers, wetlands, or percolates in to watersheds.

Researchers have also been experimenting with other methods, such as fumigation, injecting the mound, mound drenching, and surface dusting. Mound drenching entails pouring large volumes of toxic liquid into the mound. While this may affect a large portion of the mound, it is possible it may not reach the queen, thus preventing the destruction of the colony. Surface dusting is similar to mound drenching, except insecticides are applied on top of the mound and soak into the soil when wet. Mound injections use pressurising and injecting insecticides into the mound, but the queen may not be affected by this. Mounds can be eliminated effectively through fumigation. Broadcast treatment is sometimes used by spraying infected areas with agricultural equipment. Finally, spot treatment with insecticides can be used by drilling and injecting the mound with residual insecticide. [93] [379]

Aside from chemical control, other methods that can be employed against these ants include mechanical and electrical devices. However, it is unknown whether or not these devices are effective. Ant-proofing can be effective against colonies nesting inside buildings by caulking and sealing cracks, which successfully suppresses the population outside the walls. Homeowners have used their own methods to remove mounds by pouring boiling water on them or igniting them with flammable liquids. Although these methods may be effective, they are not recommended because they can be harmful to humans and the environment. [93] [379]


Ants Go Marching

F ive World War II bombers took off from a Florida airfield on Oct. 5, 1967 to bomb the American South. An article that ran that morning in the Sarasota Herald-Tribune said that three B-17s and two PV-2s laden with 10,000 pounds of death-dealing cargo each would carry out their missions “with the City of Sarasota and eastern Manatee as their targets.”

While the bombers were certainly at war, they weren’t dropping explosives. Their enemy was a millimeters-long, brownish-red insect known to scientists as Solenopsis invicta, meaning “invincible ant,” and to lay people as the fire ant, aka “ants from hell” and “them devils.” The bombers were to unload mirex, a poison usually applied to grits, onto the critter.

By the late 1960s, the fire ant had been in the American South for more than 30 years. Southerners spoke of ruined crops, destroyed wildlife, and the ants’ fiery sting. How much damage the ants had actually caused was uncertain, but it was enough for the U.S. Department of Agriculture (USDA) to declare war on the pest. During an 11-year campaign, more than 143 million pounds of mirex 1 were dropped across 77,220 square miles of land from Texas to Florida, costing close to $200 million. The outcome? The ants nearly doubled their range. The mirex, which was later found to be a carcinogen, persisted in the environment for decades, accumulating in birds’ eggs, mammals’ milk, and human tissues. The world’s leading ant researcher, E.O. Wilson, dubbed the mirex program the “Vietnam of entomology.”

Today, if you draw a line from Virginia Beach to Nashville to Abilene in west Texas, you’ll find fire ants everywhere below it, as well as in Southern California. 2 The ants’ annual impact on the economy, environment, and quality of life in the United States totals $6 billion, according to entomologists at Texas A&M University. In Texas alone they rack up $1.2 billion each year: $47 million at golf courses $64 million at cemeteries (the ants love the open and slightly overgrown habitat around tombs) and as much as $255 million in the cattle industry. They cause other problems too. In Virginia Beach, 30-year-old former marine Bradley Johnson was stung by fire ants while working outside—and died of anaphylactic shock. On at least one occasion, fire ants invaded an elementary school in Tennessee to get candy stashed in kids’ lockers. At Greystone Retirement Community in Huntsville, Ala., a staffer found 79-year-old Lucille Devers 3 covered in fire ants, which were crawling from her mouth, nose, ears, and hair: The ants frequently enter nursing homes, attracted by crumbs left in residents’ beds. And scientists anticipate that the ants will keep expanding their range. Climate change and crossbreeding with species more tolerant of cold may enable them to settle farther north.

I, on the contrary, moved south. Last August, my girlfriend, Karen, and I sold most of our belongings, piled two cats, a terrier, and a pudgy brown Chihuahua named Jazzy-B, into a minivan and drove from New York City to New Orleans. A few weeks later, we toasted our arrival with a picnic in City Park. As we rolled up our blanket, our legs suddenly caught fire. Under the glow of a streetlight, we slipped off our pants to find our legs crawling with ants. I received more than 200 stings, which formed welts the size of drink coasters, and my ears and throat swelled up. Half a dozen Benadryls later I was fine, except for hundreds of very itchy pustules. Luckily I wasn’t anaphylactic, but between 0.5 and 5 percent of the U.S. population is. 4 For the most allergic, such stings can cause spasms of the bronchial muscles or coronary arteries, preventing oxygen from entering the bloodstream and causing death within minutes. When a few weeks later Jazzy-B stepped on an ant mound and howled, spending the rest of the day licking his paw, I was ready to declare my own war on the fire ant. But first I had to research my enemy.

Manhattan’s God of Insects

The corpse-colored door hides in plain sight among SoHo’s posh boutiques. I pass by it at first, missing the “107 Spring” address plaque in tarnished brass. Peering at the buzzer to verify the tenants, I spot the name Stevens. Written. READ MORE

The range of Solenopsis invicta covers a vast wetland in southern Brazil and Paraguay known as the Pantanal. Sometime in the early 1930s the ants stowed away in coffee sacks, soil, or hollow logs piled in the bottom of a cargo ship. The voyagers were probably just a handful of queens, each about the width of a thumbnail. They ate what they could find down in the hold—cockroaches, beetles, sugary cargo, and, when the pickings got slim, themselves, digesting their own wing muscles and fat reserves. Their ship may well have steamed past Rio de Janeiro, the mouth of the Amazon, and the lush peaks of the Antilles, all while their first batch of eggs gestated in their abdomens. In Mobile, Ala., the ship docked, the sacks or soil or logs were unloaded, and the queens disembarked. Beneath the port’s loading cranes and circling seagulls, perhaps in a patch of newly cut grass, the ants established their first colony: a mound of soil honeycombed with chambers and tunnels that ran as much as four feet deep. They like to build mounds in disturbed habitats such as the edge of a road, the side of a building, pastures, lawns, or near a busy port. 5 They eat pretty much anything—seeds, nectar, worms, weevils, butterflies, and even baby sea turtles, snakes, and alligators—catching the young as they hatch.

Colonies consist of queens, workers, and sexuals, also called alates. Queens lay eggs that hatch into larvae—tiny, white, ricelike kernels that develop into adult ants. Alates are born at the end of winter or the beginning of spring, and spend their lives fattening up and preparing for their mating flight. Workers begin life as nurses, grooming and feeding the brood and the queen. They move on to tasks like nest maintenance and sanitation. In their golden years, workers become foragers, handling the colony’s most dangerous job, as it exposes them to predators and the elements. As the life in them winds down, workers act as their own pallbearers, lying down to die in a mass ant grave called the refuse pile.

To trace the ants’ seemingly unstoppable march through the South, I decided to follow their path from where they first staked their claim to American soil. Just before I left, as if an ominous sign from some myrmecological god, a mound swelled up in our backyard. I headed out on my odyssey nonetheless, undaunted.

As the life in them winds down, workers act as their own pallbearers, lying down to die in a mass ant grave.

Mobile, the twelfth largest port in the nation, which last year handled 26 million tons of cargo, greeted me with loading cranes that looked like characters from some gigantic industrial alphabet, a stench of diesel fuel, sea spray that hung in the air, and—sure enough—fire ant mounds. Near the port, cattails poked out the top of one. Its surface was lifeless, but when I kicked it lightly, seeking revenge for my itchy pustules, the creatures swarmed out. They might have been the great-great-great-great-great-great-great-great-great-great-great-grandchildren (queens live about seven years) of the group that had steamed here from South America back in the 1930s.

A short walk from the port was a neighborhood of arching oaks and trim ranch homes with well-clipped lawns. I stopped at 550 Charleston Street, the childhood home of E.O. Wilson—to ponder the fact that the planet’s most famous ant biologist grew up at the epicenter of the planet’s most famous ant invasion. In the weedy vacant lot next door, a young Wilson studied beetles, butterflies, spiders, and all manner of ants, including Solenopsis invicta, whose mound he first discovered in May 1942, at age 12. “I still remember the species I found, in vivid detail,” Wilson wrote in Naturalist, a book about his insect-happy childhood. Now the neighborhood appeared to be fire ant-less—thanks to the tireless, creative, and brutal efforts of its human inhabitants.

Sitting next to a table that held a rifle and a dead squirrel, Lonnie Rayford, a 72-year-old farmer, told me he “done got bit” many a time. In his opinion, one science does not really confirm, just plain grits were good enough to kill the pests. “Dig a hole and put grits in there, they gonna take it down to the bottom and give it to the queen,” he said. “Them grits will kill them.” Down the street, a husky man pulling weeds from his garden told me he used poison.

From Mobile, I headed northeast to Montgomery, where I drove by the state capitol, a creamy white dome calling to mind a magnificent wedding cake. I stopped at Dixie Hardware to learn about fire ant control from the pros. A bearded worker named John showed me to aisle nine, which was an exterminator’s nirvana.

“You got roach and ant killer, you got ant killer, you got Ant Max—it’s some kind of trap,” he said, holding up a rectangular red-and-yellow box that looked like it could have contained movie theater candies, except for a drawing of a vicious fire ant on the side. The best seller was a big orange bag that read “Spectracide Fire Ant Killer Mound Destroyer.”

John’s coworker Richard explained to me the challenges and intricacies of mass insecticide. The problem with poison was that ants often simply moved into the neighbor’s yard, requiring neighborhood-wide poisoning efforts—in other words, it took a village to rid itself of the pests. Another trick involved two people shoveling ants from separate mounds into one another—according to Richard, the ants will assassinate the foreign queens. And then there is gasoline, apparently Alabama’s preferred eradication method. “Take a broom handle, stick it down the mound, pour gas on it, and I know it’s gonna burn whatever is in there,” Richard said excitedly.

Eliminating fire ants seemed a bit like making cornbread every Southerner had his own favorite recipe. By this time, my welts were long gone and I began to feel bad for the little ants. Especially since I understood that their inexorable spread was, in large part, our own fault.

Naturally, ants don’t really spread that fast: During the 1930s and 1940s fire ants migrated out from Mobile at the rate of about 4 to 5 miles a year, a distance thought to be covered mostly in mating flights. On warm days following soaking spring or summer rains, alates exit the mound surrounded by a gang of worker bodyguards and launch into the air to mate—which they do in large clouds called mating swarms. Males inject females with a lifetime supply of sperm and then die. Newly mated queens land, kick off their wings, and scurry away to start new colonies, avoiding predators like dragonflies, which love to gobble their sperm-filled abdomens. Queens typically fly a few miles during mating flights, and if the wind is right, they can fly more than ten. But that’s it.

Ants can also move when disturbed. In such a case an entire colony moves, but typically only a few feet, a migration initiated automatically by the workers. And a good many fire ant colonies across the South—known as polygyne colonies, meaning those with more than one queen—can actually move without mating flights, by budding off like yeast. A queen and some workers will simply wander off to start a new colony, but, again, they won’t go far. The most successful means for fire ant migration, however, is us. Humans.

Eliminating fire ants seemed a bit like making cornbread every Southerner had his own favorite recipe.

In 1949 fire ants were mostly situated in a roughly 50-mile-wide radius around Mobile and in a few spots in central Alabama and Mississippi. But as Americans moved to the suburbs during the 1950s, desirous of white picket fences, front lawns, and ornamental shrubs, the nursery trade boomed. Soil, plants, and pots were shipped across states and counties. Hidden in the dirt caked on a bulldozer, in the root ball of a nursery plant, or in the bed of a pickup truck, a newly mated queen can travel hundreds of miles. Thanks to our horticultural aspirations, by 1957 S. invicta were in every Southern state except Kentucky and the Virginias.

It was around then that the U.S. Department of Agriculture set out to eliminate the invaders. 6 In 1958 it established a quarantine that restricted the shipment of soil, nursery plants, and baled hay from areas infested with fire ants to those without, unless the products were first treated with insecticides. Between 1957 and 1962 the USDA coated 2.5 million acres with clay granules containing the insecticide heptachlor. It did indeed kill fire ants, but also blackbirds, quail, geese, frogs, dogs, cats, crabs, and millions of fish—a famous fiasco that helped inspire Rachel Carson’s Silent Spring. Few at the USDA seemed to heed her warning, so the war continued. That entomological Vietnam, which lasted from 1964 to 1975, according to The Fire Ants, a book by myrmecologist Walter Tschinkel, left 24 to 33 percent of Southerners with mirex in their body tissues.

Meanwhile, the invincible creatures nearly doubled their range, and some scientists speculated the insecticide was the cause. The poison often eliminated all the ant species where it was applied, giving S. invicta, which is thought to be a better colony founder, a chance to become the dominant type upon recolonization. The secrets of their survival are not entirely known, but Tschinkel thinks it has something to do with large colonies, large numbers of alates, large dispersal distances, and a long mating flight season.

The fire ant front line runs through the middle of Tennessee. I continued north on the ants’ path and pulled off the highway in McMinnville, the heart of the state’s nursery industry and just inside the line. Here, nursery growers have to douse plants’ roots, where newly mated queens sometimes cling undetected, with Chlorpyrifos, a toxic and expensive insecticide. Tommy Boyd, co-owner of Boyd & Boyd Nursery, told me his workers did the task while wearing gloves and respirators. He refused to touch the stuff himself because the insecticide gave him horrible headaches. “I don’t want to die over some chemical,” Boyd told me.

I drove down a windy lane a short time later that brought me to Tennessee State University’s Otis L. Floyd Nursery Research Center. Here I spoke with a gentle entomologist in a flannel shirt named Jason Oliver, who works on a less destructive and more natural ant eradication method: A project to introduce phorid flies, who prey on the ants back in Pantanal. In the late 1990s USDA researchers went to South America to capture different species of phorid flies, which they studied at an Animal and Plant Health Inspection Service (APHIS) lab in Gainesville, Fla., to determine the best one to introduce to various parts of the American South. Oliver’s phorid flies are shipped from the lab to be released in Tennessee.

Phorids lay their eggs in the fire ants’ thorax, and when the eggs hatch, the ants’ heads fall off. 7 Oliver showed me a video he had filmed in a petri dish, a fly implanting eggs in an ant. A tiny dot buzzed about some ants in the blink of an eye it brushed one of them, then continued flying. In that moment the fly had injected the eggs. It happened so quickly I asked Oliver to replay the video. It seemed like a perfect solution. But as impressive as the tiny fly was, it wasn’t going to decapitate a whole colony, just make ants more scared to leave their nests. “We’re always going to have fire ants,” Oliver told me. “There is no way to eliminate them.”

Weaving through rolling hills dotted with nurseries, I drove northwest from McMinnville, skirting the S. invicta front line: To the south, elementary schools, nursing homes, and greenhouses were being invaded, while to the north, the land was, supposedly, fire ant-free. The road took me through the area inundated in the catastrophic floods of May 2010. In Nashville, the Cumberland River rose 33 feet, flooding much of the city, including the Country Music Hall of Fame, the Grand Ole Opry House, and an untold number of fire ant mounds. Contrary to expectations, the ants didn’t drown. Instead, they metastasized further.

The ants would have been well prepared, Louisiana State University entomologist Linda Hooper-Bui explained to me. In their homeland the Pantanal floods happen annually, so they learned to raft. As waters rise, ants evacuate lower tunnels and move higher in their mound, eventually gathering on top. Using hooks, called tarsi, on the tips of their legs, ants latch onto one another and create rafts. Late-stage larvae are covered in hook-like hairs that trap air, encasing them in bubbles. Worker ants stack these larvae three to five thick, forming pontoons that keep the rafts afloat. They place the queen in the middle with pupae and early-stage larvae, which don’t have the crucial hairs to form the bubbles. Save the clumps of eggs workers carry in their jaws and a small amount of liquid food stored in their bodies that will last only a few days, the ants bring nothing aboard. Moreover, as the raft sets off, tipped into the water by the workers, they fling male alates overboard. If the raft is afloat longer than four days, the ants will begin to eat the brood—although not the ones used to make the raft. Rafts can hold together for as long as 21 days, surely long enough to survive the swollen Cumberland River.

Or at least this is what Steve Powell, an entomologist with the state of Tennessee, believes. In February of this year he received a call reporting fire ants in Cumberland City, a remote town about 80 miles north from Nashville and far above the front line. “There’s no rhyme or reason why they should be there, so far from other fire ant infestations,” Powell said. “If I had to guess, I’d say it was the flood.”

Phorids lay their eggs in the fire ants’ thorax, and when the eggs hatch, the ants’ heads fall off.

Continuing my journey, I drove farther north into Cumberland City—a ramshackle collection of vine-ensnarled clapboard homes and shuttered storefronts on steep forested hills above the Cumberland River. On the edge of town sat a massive Tennessee Valley Authority coal plant with four 1,000-foot-tall smokestacks, some of the largest on earth. Beside the plant was a small restaurant with foggy windows, where farmers in overalls sat at low tables gobbling catfish and pork chops. I was looking for someone to speak with about the ants, expecting a thrilling validation of Powell’s rafting theory. Instead I found an unsurprising surprise: Bailey Gafford, a weatherworn cattle farmer in mud-splattered boots, told me fire ants had been in Cumberland City since before the floods. He even suggested an innovative method of eradication I hadn’t heard before: “Put snuff around the mound. They come out and you set ’em on fire.”

On my way out of Cumberland City I stopped at a Civil War cemetery, where wildflowers cloaked weather-beaten tombs and atop a small hill stood a dozen crude cabins, campground for a long-forgotten battle. Our own battle against the ant was still in full swing, however, and it didn’t look like we were winning. The war on S. invicta suddenly fit into a broader picture, that of the Insecticide-Military-Industrial Complex. It was around the time that President Obama announced, concerning the nation’s ongoing war on terrorism, that we cannot remain on “a perpetual wartime footing.” The statement also seemed to apply to our war against the fire ants.

Besides, no matter how we perfect our tactics, these ultimate invaders seem to find new ways to advance. Somehow, Solenopsis invicta crossbred with Solenopsis richteri, another species that came from Pantanal by cargo ship 8 to Mobile, in 1918. Originally S. invicta drove out S. richteri, a less aggressive variety that prefers cooler weather and might have found the South too hot. But in the 1980s a hybrid of the two was discovered. No one knows exactly how the hybridization occurred—in certain parts of the Pantanal the two species’ territories overlap, but they don’t interbreed. Here they do, which is perhaps the most ominous sign. Purebred S. invicta don’t survive more than three or four days in temperatures below freezing. Neither does S. richteri. But the hybrid survives freezing temperatures better than either pure species, according to a 2002 study in Environmental Entomology.

Could a hybrid—or perhaps a hybrid of a hybrid—one day push that front line farther north, to Washington D.C., and Philadelphia? What about New York City, with its 8 million residents as clueless as I once was? Recently the ants were brought by ship from the U.S. to Australia and also Taiwan from there they invaded China. According to a 2004 paper in Biological Invasions, fire ants could potentially infest France, Italy, Greece, Japan, South Korea, Mexico, Central America, and large parts of Africa and India. Is there a way for us to coexist with the creatures? I was still hopeful.

Upon returning to New Orleans I discovered the fire ant mound in our backyard had quadrupled in size. It now towered above the grass blades like Kilimanjaro. As I stood dumbfounded, contemplating what to do, a potato bug ascended the northern flank, an agile alpinist indeed, somehow not inducing a swarm. I wanted to be like the potato bug and coexist with the mound, dance my fingers upon its slopes without getting stung, but I knew it was impossible. Even if Karen and I somehow avoided the nest, there were our animals to think of—the cats, the terrier, and Jazzy-B, who at that moment was watching me from inside with curious dog eyes. Last time he got off easy, but if he received hundreds of stings, the poison would surely overwhelm his little Chihuahua system. The choice was clear. I would have to eradicate the mound.

The abundance of killing choices was what puzzled me: Pit rival colonies against each other, grits, gasoline, a broom and gasoline, poison and, if poison, which one? In the end I decided on a less ecologically invasive technique no one had mentioned except for Oliver—he muttered it under his breath toward the end of our conversation as if revealing a secret that embarrassed him: hot water. Ant Max and Spectracide Fire Ant Killer Mound Destroyer don’t seem to want you to know about it.

I wanted to be like the potato bug and coexist with the mound, dance my fingers upon its slopes without getting stung.

With Jazzy-B and all the others safely inside, I emptied the cat litter box, dusted it with baby powder so the ants couldn’t crawl up the sides, and shoveled the mound into it, quickly adding boiling water to fill it. A second pot of boiling water went into the open mound, to seep down into the interior tunnels and chambers, and then a third and a fourth, too, just to be sure I got the queen. There was an initial explosion of red, with numerous of the brood being moved about, but the water cooked them instantly and, within the hour, the mound was dead.

I gathered my household armor and walked back toward the house, with far from a satisfying sense of achievement. I might have won this battle, but we were still losing the war. Inevitably, another mound would pop up. My “victory” was just a reprieve.

Justin Nobel’s stories about science and culture have appeared in Popular Mechanics, Orion, and Tin House. For his book, Standing Still in a Concrete Jungle, Justin spent extended periods of time in iconic New York City spots observing minutiae. He’s presently working on a book about forgotten small towns of the American South.

This article was originally published in our “In Transit” issue in July, 2013.


This is what it means if you see ants in your house

There is no secret that ants are exceptionally hardworking, dedicated, skilled and the most organized insects of all. They live by strict rules, believe in teamwork and are always engaged in their own work. We commonly find a colony of ants marching into our house in places like the kitchen and overlook it. But do you know that there is a story behind every animal or bird behaviour?

Ants also give some hints about the positive and negative incidents that are about to happen in your life. As per Jyotish Shastra, ants are linked to good luck and wealth.

02 /7 Red and black ants

Black ants are considered quite auspicious. So if you see black ants roaming around your house then it means that soon there will be a sharp rise in your wealth. One the other hand, red ants are considered to bring bad luck. Red ants in the house means loss of wealth.

03 /7 Place matters

Black ants coming out from a rice box means you will soon get money from somewhere. If ants are found in places where you store your gold jewellery, then it indicates that you will get gold items.

04 /7 Directions

If ants are coming from the North direction then it indicates happiness and if they are coming from South then it indicates profits. Ants marching from East means you might hear some negative news and if they are present in the West direction then there are high chances that soon you will go abroad.

05 /7 Red ants

Red ants are believed to bring bad omen so if you see them in your house, so immediately remove them. However, if red ants exit from your house with their eggs in their mouth then it is a good sign.

06 /7 Black ants

Although black ants are considered auspicious and indicate happiness, peace, prosperity, they should not be present in a huge number. If they are breeding in your house then take appropriate steps to show them the way out.

07 /7 Other signs

Apart from red ants, beehives and termites also bring bad luck. Beehives and termites mean that the head of the family will suffer from some health issues.


Southern toads alter their behavior in response to red-imported fire ants

We used the southern toad (Anaxyrus terrestris) as a model species to explore how an invasive species, the red-imported fire ant (Solenopsis invicta hereafter RIFA), influences amphibian predator avoidance and movement behaviors. Our objective was to determine if toads spent less time near and moved more frequently in the presence of RIFAs compared to pyramid ants by comparing behavioral reactions of toads to RIFAs versus a control and pyramid ants versus a control. Laboratory experiments involved three treatments including no ants, RIFAs, and native pyramid ants (Dorymyrmex bureni) within an experimental arena. We randomly placed ants into one of two containers located at each end of the arena. For each trial we placed a toad into the experimental arena, allowed the toad to acclimate and then recorded its behavior. We calculated the proportion of time the toad spent near ants and the number of movements completed by each toad. Comparing the RIFA treatment to the pyramid ant treatment, toads spent 35 % less time on the half of the experimental arena near RIFAs (P = 0.0304). Toad movements were 1.5 times more frequent in trials with RIFAs than pyramid ants (P = 0.0488). We propose that southern toads associate RIFAs either with increased predation risk or risk of injury compared to pyramid ants. Although the behaviors we observed might lessen the direct effects of RIFAs on southern toads via predation and injury, the indirect effects of increased movement and avoidance of RIFAs could also influence toad fitness by decreasing reproductive and foraging success.

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Ants Go Marching

F ive World War II bombers took off from a Florida airfield on Oct. 5, 1967 to bomb the American South. An article that ran that morning in the Sarasota Herald-Tribune said that three B-17s and two PV-2s laden with 10,000 pounds of death-dealing cargo each would carry out their missions “with the City of Sarasota and eastern Manatee as their targets.”

While the bombers were certainly at war, they weren’t dropping explosives. Their enemy was a millimeters-long, brownish-red insect known to scientists as Solenopsis invicta, meaning “invincible ant,” and to lay people as the fire ant, aka “ants from hell” and “them devils.” The bombers were to unload mirex, a poison usually applied to grits, onto the critter.

By the late 1960s, the fire ant had been in the American South for more than 30 years. Southerners spoke of ruined crops, destroyed wildlife, and the ants’ fiery sting. How much damage the ants had actually caused was uncertain, but it was enough for the U.S. Department of Agriculture (USDA) to declare war on the pest. During an 11-year campaign, more than 143 million pounds of mirex 1 were dropped across 77,220 square miles of land from Texas to Florida, costing close to $200 million. The outcome? The ants nearly doubled their range. The mirex, which was later found to be a carcinogen, persisted in the environment for decades, accumulating in birds’ eggs, mammals’ milk, and human tissues. The world’s leading ant researcher, E.O. Wilson, dubbed the mirex program the “Vietnam of entomology.”

Today, if you draw a line from Virginia Beach to Nashville to Abilene in west Texas, you’ll find fire ants everywhere below it, as well as in Southern California. 2 The ants’ annual impact on the economy, environment, and quality of life in the United States totals $6 billion, according to entomologists at Texas A&M University. In Texas alone they rack up $1.2 billion each year: $47 million at golf courses $64 million at cemeteries (the ants love the open and slightly overgrown habitat around tombs) and as much as $255 million in the cattle industry. They cause other problems too. In Virginia Beach, 30-year-old former marine Bradley Johnson was stung by fire ants while working outside—and died of anaphylactic shock. On at least one occasion, fire ants invaded an elementary school in Tennessee to get candy stashed in kids’ lockers. At Greystone Retirement Community in Huntsville, Ala., a staffer found 79-year-old Lucille Devers 3 covered in fire ants, which were crawling from her mouth, nose, ears, and hair: The ants frequently enter nursing homes, attracted by crumbs left in residents’ beds. And scientists anticipate that the ants will keep expanding their range. Climate change and crossbreeding with species more tolerant of cold may enable them to settle farther north.

I, on the contrary, moved south. Last August, my girlfriend, Karen, and I sold most of our belongings, piled two cats, a terrier, and a pudgy brown Chihuahua named Jazzy-B, into a minivan and drove from New York City to New Orleans. A few weeks later, we toasted our arrival with a picnic in City Park. As we rolled up our blanket, our legs suddenly caught fire. Under the glow of a streetlight, we slipped off our pants to find our legs crawling with ants. I received more than 200 stings, which formed welts the size of drink coasters, and my ears and throat swelled up. Half a dozen Benadryls later I was fine, except for hundreds of very itchy pustules. Luckily I wasn’t anaphylactic, but between 0.5 and 5 percent of the U.S. population is. 4 For the most allergic, such stings can cause spasms of the bronchial muscles or coronary arteries, preventing oxygen from entering the bloodstream and causing death within minutes. When a few weeks later Jazzy-B stepped on an ant mound and howled, spending the rest of the day licking his paw, I was ready to declare my own war on the fire ant. But first I had to research my enemy.

Ingenious: Cornelia Hesse-Honegger

For someone who has spent decades drawing deformed insects, Cornelia Hesse-Honegger is remarkably normal: Warm, effusive, and quick to laugh, Hesse-Honegger combines the holism and intuition of an artist with the curiosity and obsession with detail of a scientist. Next. READ MORE

The range of Solenopsis invicta covers a vast wetland in southern Brazil and Paraguay known as the Pantanal. Sometime in the early 1930s the ants stowed away in coffee sacks, soil, or hollow logs piled in the bottom of a cargo ship. The voyagers were probably just a handful of queens, each about the width of a thumbnail. They ate what they could find down in the hold—cockroaches, beetles, sugary cargo, and, when the pickings got slim, themselves, digesting their own wing muscles and fat reserves. Their ship may well have steamed past Rio de Janeiro, the mouth of the Amazon, and the lush peaks of the Antilles, all while their first batch of eggs gestated in their abdomens. In Mobile, Ala., the ship docked, the sacks or soil or logs were unloaded, and the queens disembarked. Beneath the port’s loading cranes and circling seagulls, perhaps in a patch of newly cut grass, the ants established their first colony: a mound of soil honeycombed with chambers and tunnels that ran as much as four feet deep. They like to build mounds in disturbed habitats such as the edge of a road, the side of a building, pastures, lawns, or near a busy port. 5 They eat pretty much anything—seeds, nectar, worms, weevils, butterflies, and even baby sea turtles, snakes, and alligators—catching the young as they hatch.

Colonies consist of queens, workers, and sexuals, also called alates. Queens lay eggs that hatch into larvae—tiny, white, ricelike kernels that develop into adult ants. Alates are born at the end of winter or the beginning of spring, and spend their lives fattening up and preparing for their mating flight. Workers begin life as nurses, grooming and feeding the brood and the queen. They move on to tasks like nest maintenance and sanitation. In their golden years, workers become foragers, handling the colony’s most dangerous job, as it exposes them to predators and the elements. As the life in them winds down, workers act as their own pallbearers, lying down to die in a mass ant grave called the refuse pile.

To trace the ants’ seemingly unstoppable march through the South, I decided to follow their path from where they first staked their claim to American soil. Just before I left, as if an ominous sign from some myrmecological god, a mound swelled up in our backyard. I headed out on my odyssey nonetheless, undaunted.

As the life in them winds down, workers act as their own pallbearers, lying down to die in a mass ant grave.

Mobile, the twelfth largest port in the nation, which last year handled 26 million tons of cargo, greeted me with loading cranes that looked like characters from some gigantic industrial alphabet, a stench of diesel fuel, sea spray that hung in the air, and—sure enough—fire ant mounds. Near the port, cattails poked out the top of one. Its surface was lifeless, but when I kicked it lightly, seeking revenge for my itchy pustules, the creatures swarmed out. They might have been the great-great-great-great-great-great-great-great-great-great-great-grandchildren (queens live about seven years) of the group that had steamed here from South America back in the 1930s.

A short walk from the port was a neighborhood of arching oaks and trim ranch homes with well-clipped lawns. I stopped at 550 Charleston Street, the childhood home of E.O. Wilson—to ponder the fact that the planet’s most famous ant biologist grew up at the epicenter of the planet’s most famous ant invasion. In the weedy vacant lot next door, a young Wilson studied beetles, butterflies, spiders, and all manner of ants, including Solenopsis invicta, whose mound he first discovered in May 1942, at age 12. “I still remember the species I found, in vivid detail,” Wilson wrote in Naturalist, a book about his insect-happy childhood. Now the neighborhood appeared to be fire ant-less—thanks to the tireless, creative, and brutal efforts of its human inhabitants.

Sitting next to a table that held a rifle and a dead squirrel, Lonnie Rayford, a 72-year-old farmer, told me he “done got bit” many a time. In his opinion, one science does not really confirm, just plain grits were good enough to kill the pests. “Dig a hole and put grits in there, they gonna take it down to the bottom and give it to the queen,” he said. “Them grits will kill them.” Down the street, a husky man pulling weeds from his garden told me he used poison.

From Mobile, I headed northeast to Montgomery, where I drove by the state capitol, a creamy white dome calling to mind a magnificent wedding cake. I stopped at Dixie Hardware to learn about fire ant control from the pros. A bearded worker named John showed me to aisle nine, which was an exterminator’s nirvana.

“You got roach and ant killer, you got ant killer, you got Ant Max—it’s some kind of trap,” he said, holding up a rectangular red-and-yellow box that looked like it could have contained movie theater candies, except for a drawing of a vicious fire ant on the side. The best seller was a big orange bag that read “Spectracide Fire Ant Killer Mound Destroyer.”

John’s coworker Richard explained to me the challenges and intricacies of mass insecticide. The problem with poison was that ants often simply moved into the neighbor’s yard, requiring neighborhood-wide poisoning efforts—in other words, it took a village to rid itself of the pests. Another trick involved two people shoveling ants from separate mounds into one another—according to Richard, the ants will assassinate the foreign queens. And then there is gasoline, apparently Alabama’s preferred eradication method. “Take a broom handle, stick it down the mound, pour gas on it, and I know it’s gonna burn whatever is in there,” Richard said excitedly.

Eliminating fire ants seemed a bit like making cornbread every Southerner had his own favorite recipe. By this time, my welts were long gone and I began to feel bad for the little ants. Especially since I understood that their inexorable spread was, in large part, our own fault.

Naturally, ants don’t really spread that fast: During the 1930s and 1940s fire ants migrated out from Mobile at the rate of about 4 to 5 miles a year, a distance thought to be covered mostly in mating flights. On warm days following soaking spring or summer rains, alates exit the mound surrounded by a gang of worker bodyguards and launch into the air to mate—which they do in large clouds called mating swarms. Males inject females with a lifetime supply of sperm and then die. Newly mated queens land, kick off their wings, and scurry away to start new colonies, avoiding predators like dragonflies, which love to gobble their sperm-filled abdomens. Queens typically fly a few miles during mating flights, and if the wind is right, they can fly more than ten. But that’s it.

Ants can also move when disturbed. In such a case an entire colony moves, but typically only a few feet, a migration initiated automatically by the workers. And a good many fire ant colonies across the South—known as polygyne colonies, meaning those with more than one queen—can actually move without mating flights, by budding off like yeast. A queen and some workers will simply wander off to start a new colony, but, again, they won’t go far. The most successful means for fire ant migration, however, is us. Humans.

Eliminating fire ants seemed a bit like making cornbread every Southerner had his own favorite recipe.

In 1949 fire ants were mostly situated in a roughly 50-mile-wide radius around Mobile and in a few spots in central Alabama and Mississippi. But as Americans moved to the suburbs during the 1950s, desirous of white picket fences, front lawns, and ornamental shrubs, the nursery trade boomed. Soil, plants, and pots were shipped across states and counties. Hidden in the dirt caked on a bulldozer, in the root ball of a nursery plant, or in the bed of a pickup truck, a newly mated queen can travel hundreds of miles. Thanks to our horticultural aspirations, by 1957 S. invicta were in every Southern state except Kentucky and the Virginias.

It was around then that the U.S. Department of Agriculture set out to eliminate the invaders. 6 In 1958 it established a quarantine that restricted the shipment of soil, nursery plants, and baled hay from areas infested with fire ants to those without, unless the products were first treated with insecticides. Between 1957 and 1962 the USDA coated 2.5 million acres with clay granules containing the insecticide heptachlor. It did indeed kill fire ants, but also blackbirds, quail, geese, frogs, dogs, cats, crabs, and millions of fish—a famous fiasco that helped inspire Rachel Carson’s Silent Spring. Few at the USDA seemed to heed her warning, so the war continued. That entomological Vietnam, which lasted from 1964 to 1975, according to The Fire Ants, a book by myrmecologist Walter Tschinkel, left 24 to 33 percent of Southerners with mirex in their body tissues.

Meanwhile, the invincible creatures nearly doubled their range, and some scientists speculated the insecticide was the cause. The poison often eliminated all the ant species where it was applied, giving S. invicta, which is thought to be a better colony founder, a chance to become the dominant type upon recolonization. The secrets of their survival are not entirely known, but Tschinkel thinks it has something to do with large colonies, large numbers of alates, large dispersal distances, and a long mating flight season.

The fire ant front line runs through the middle of Tennessee. I continued north on the ants’ path and pulled off the highway in McMinnville, the heart of the state’s nursery industry and just inside the line. Here, nursery growers have to douse plants’ roots, where newly mated queens sometimes cling undetected, with Chlorpyrifos, a toxic and expensive insecticide. Tommy Boyd, co-owner of Boyd & Boyd Nursery, told me his workers did the task while wearing gloves and respirators. He refused to touch the stuff himself because the insecticide gave him horrible headaches. “I don’t want to die over some chemical,” Boyd told me.

I drove down a windy lane a short time later that brought me to Tennessee State University’s Otis L. Floyd Nursery Research Center. Here I spoke with a gentle entomologist in a flannel shirt named Jason Oliver, who works on a less destructive and more natural ant eradication method: A project to introduce phorid flies, who prey on the ants back in Pantanal. In the late 1990s USDA researchers went to South America to capture different species of phorid flies, which they studied at an Animal and Plant Health Inspection Service (APHIS) lab in Gainesville, Fla., to determine the best one to introduce to various parts of the American South. Oliver’s phorid flies are shipped from the lab to be released in Tennessee.

Phorids lay their eggs in the fire ants’ thorax, and when the eggs hatch, the ants’ heads fall off. 7 Oliver showed me a video he had filmed in a petri dish, a fly implanting eggs in an ant. A tiny dot buzzed about some ants in the blink of an eye it brushed one of them, then continued flying. In that moment the fly had injected the eggs. It happened so quickly I asked Oliver to replay the video. It seemed like a perfect solution. But as impressive as the tiny fly was, it wasn’t going to decapitate a whole colony, just make ants more scared to leave their nests. “We’re always going to have fire ants,” Oliver told me. “There is no way to eliminate them.”

Weaving through rolling hills dotted with nurseries, I drove northwest from McMinnville, skirting the S. invicta front line: To the south, elementary schools, nursing homes, and greenhouses were being invaded, while to the north, the land was, supposedly, fire ant-free. The road took me through the area inundated in the catastrophic floods of May 2010. In Nashville, the Cumberland River rose 33 feet, flooding much of the city, including the Country Music Hall of Fame, the Grand Ole Opry House, and an untold number of fire ant mounds. Contrary to expectations, the ants didn’t drown. Instead, they metastasized further.

The ants would have been well prepared, Louisiana State University entomologist Linda Hooper-Bui explained to me. In their homeland the Pantanal floods happen annually, so they learned to raft. As waters rise, ants evacuate lower tunnels and move higher in their mound, eventually gathering on top. Using hooks, called tarsi, on the tips of their legs, ants latch onto one another and create rafts. Late-stage larvae are covered in hook-like hairs that trap air, encasing them in bubbles. Worker ants stack these larvae three to five thick, forming pontoons that keep the rafts afloat. They place the queen in the middle with pupae and early-stage larvae, which don’t have the crucial hairs to form the bubbles. Save the clumps of eggs workers carry in their jaws and a small amount of liquid food stored in their bodies that will last only a few days, the ants bring nothing aboard. Moreover, as the raft sets off, tipped into the water by the workers, they fling male alates overboard. If the raft is afloat longer than four days, the ants will begin to eat the brood—although not the ones used to make the raft. Rafts can hold together for as long as 21 days, surely long enough to survive the swollen Cumberland River.

Or at least this is what Steve Powell, an entomologist with the state of Tennessee, believes. In February of this year he received a call reporting fire ants in Cumberland City, a remote town about 80 miles north from Nashville and far above the front line. “There’s no rhyme or reason why they should be there, so far from other fire ant infestations,” Powell said. “If I had to guess, I’d say it was the flood.”

Phorids lay their eggs in the fire ants’ thorax, and when the eggs hatch, the ants’ heads fall off.

Continuing my journey, I drove farther north into Cumberland City—a ramshackle collection of vine-ensnarled clapboard homes and shuttered storefronts on steep forested hills above the Cumberland River. On the edge of town sat a massive Tennessee Valley Authority coal plant with four 1,000-foot-tall smokestacks, some of the largest on earth. Beside the plant was a small restaurant with foggy windows, where farmers in overalls sat at low tables gobbling catfish and pork chops. I was looking for someone to speak with about the ants, expecting a thrilling validation of Powell’s rafting theory. Instead I found an unsurprising surprise: Bailey Gafford, a weatherworn cattle farmer in mud-splattered boots, told me fire ants had been in Cumberland City since before the floods. He even suggested an innovative method of eradication I hadn’t heard before: “Put snuff around the mound. They come out and you set ’em on fire.”

On my way out of Cumberland City I stopped at a Civil War cemetery, where wildflowers cloaked weather-beaten tombs and atop a small hill stood a dozen crude cabins, campground for a long-forgotten battle. Our own battle against the ant was still in full swing, however, and it didn’t look like we were winning. The war on S. invicta suddenly fit into a broader picture, that of the Insecticide-Military-Industrial Complex. It was around the time that President Obama announced, concerning the nation’s ongoing war on terrorism, that we cannot remain on “a perpetual wartime footing.” The statement also seemed to apply to our war against the fire ants.

Besides, no matter how we perfect our tactics, these ultimate invaders seem to find new ways to advance. Somehow, Solenopsis invicta crossbred with Solenopsis richteri, another species that came from Pantanal by cargo ship 8 to Mobile, in 1918. Originally S. invicta drove out S. richteri, a less aggressive variety that prefers cooler weather and might have found the South too hot. But in the 1980s a hybrid of the two was discovered. No one knows exactly how the hybridization occurred—in certain parts of the Pantanal the two species’ territories overlap, but they don’t interbreed. Here they do, which is perhaps the most ominous sign. Purebred S. invicta don’t survive more than three or four days in temperatures below freezing. Neither does S. richteri. But the hybrid survives freezing temperatures better than either pure species, according to a 2002 study in Environmental Entomology.

Could a hybrid—or perhaps a hybrid of a hybrid—one day push that front line farther north, to Washington D.C., and Philadelphia? What about New York City, with its 8 million residents as clueless as I once was? Recently the ants were brought by ship from the U.S. to Australia and also Taiwan from there they invaded China. According to a 2004 paper in Biological Invasions, fire ants could potentially infest France, Italy, Greece, Japan, South Korea, Mexico, Central America, and large parts of Africa and India. Is there a way for us to coexist with the creatures? I was still hopeful.

Upon returning to New Orleans I discovered the fire ant mound in our backyard had quadrupled in size. It now towered above the grass blades like Kilimanjaro. As I stood dumbfounded, contemplating what to do, a potato bug ascended the northern flank, an agile alpinist indeed, somehow not inducing a swarm. I wanted to be like the potato bug and coexist with the mound, dance my fingers upon its slopes without getting stung, but I knew it was impossible. Even if Karen and I somehow avoided the nest, there were our animals to think of—the cats, the terrier, and Jazzy-B, who at that moment was watching me from inside with curious dog eyes. Last time he got off easy, but if he received hundreds of stings, the poison would surely overwhelm his little Chihuahua system. The choice was clear. I would have to eradicate the mound.

The abundance of killing choices was what puzzled me: Pit rival colonies against each other, grits, gasoline, a broom and gasoline, poison and, if poison, which one? In the end I decided on a less ecologically invasive technique no one had mentioned except for Oliver—he muttered it under his breath toward the end of our conversation as if revealing a secret that embarrassed him: hot water. Ant Max and Spectracide Fire Ant Killer Mound Destroyer don’t seem to want you to know about it.

I wanted to be like the potato bug and coexist with the mound, dance my fingers upon its slopes without getting stung.

With Jazzy-B and all the others safely inside, I emptied the cat litter box, dusted it with baby powder so the ants couldn’t crawl up the sides, and shoveled the mound into it, quickly adding boiling water to fill it. A second pot of boiling water went into the open mound, to seep down into the interior tunnels and chambers, and then a third and a fourth, too, just to be sure I got the queen. There was an initial explosion of red, with numerous of the brood being moved about, but the water cooked them instantly and, within the hour, the mound was dead.

I gathered my household armor and walked back toward the house, with far from a satisfying sense of achievement. I might have won this battle, but we were still losing the war. Inevitably, another mound would pop up. My “victory” was just a reprieve.

Justin Nobel’s stories about science and culture have appeared in Popular Mechanics, Orion, and Tin House. For his book, Standing Still in a Concrete Jungle, Justin spent extended periods of time in iconic New York City spots observing minutiae. He’s presently working on a book about forgotten small towns of the American South.


Ingredients for the Best Homemade Natural Ant Killer

  • 1 cup of sugar
  • 1/2 cup of water
  • 1 Tablespoon of Borax. (Update! The box now looks like this: Borax Laundry Booster, 76 oz Box)

Mix it all together and you’re ready to take action!

If you have pets or kids, you’ll want to keep the solution away from them. A little is okay but too much can cause problems so it’s better to be safe. One idea is to put it in an old plastic container with holes poked in the lid for the ants to get in and put a little bit of plain sugar water (no Borax) outside of the container to lure the ants over.

Since we still have these old peel ‘n stick floors here’s what I do:

I pour a little puddle of the killing juice on the floor…

…and I take an old tupperware lid and place it over top. I propped it up with a little piece of chalk to give the ants enough room to get in.


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People and Trees: Intimately Connected Through the Ages

Photo Credit: siamsmile/Thinkstock

Trees Speak to the Soul of Human Beings

It is no wonder that trees have captured the human imagination since the beginning of time. Their strength, deeply rooted in the Earth, is an inspiration. Their trunk and branches are a wonder of nature because they stand sturdy and impenetrable most of the time, yet they can flex and sway with the wind when needed.

The whisper of a breeze in their leaves or the sight of ants marching in a straight line up or down their trunks remind us of the magic of nature that trees embody. They live for hundreds or even thousands of years, and so we revere them as keepers of past secrets and sentinels of the future.

Watching their cycles of growth, shedding of leaves, and re-flowering in the spring, people have long perceived trees as powerful symbols of life, death, and renewal. Since the beginning of time, humans have had a sense that trees are sentient beings just like us, that they can feel pain, that they bleed when they are hurt. Trees even look like us. People have a trunk trees have arms. And so we innately feel a deep connection to them.

Many people say they can feel a tree’s vibrational energy when placing their hand upon its bark. With their deep roots, trees carry significant grounding energy. We naturally feel peace and serenity when walking in the shade of trees or on a forest trail.

Trees Help Us Every Day

A recent study shows that trees remove so much pollution from the air that they “prevented 850 human deaths and 670,000 cases of acute respiratory symptoms in 2010 alone.” When an insect called the emerald ash borer killed off a significant number of trees in the American Midwest in the 1990’s and 2000’s, rates of human death from cardiovascular and respiratory illness increased.

More difficult to quantify is the psychological effect that trees have on people. People who spend time outdoors, or even those who have access to windows looking out at trees, have been shown to have better health than those who do not.

The Universal Tree of Life: Both Ancient and Modern

The concept of a Tree of Life, often symbolizing the connections between all life forms, is found in many religions and philosophies, dating back as early as ancient Egypt. The Egyptian tree of life symbolized creation and represented the chain of events that brought everything into existence.

Fast forward to modern science. The tree has become the quintessential symbol of biological evolution, as its ever-branching image poignantly depicts the unmistakable interconnections between all living species on the Earth.

The Tree Leaf and Eternal Life

Consider this beautiful commentary from Thich Nhat Hanh reflecting on a tree leaf:

“I asked the leaf whether it was frightened because it was autumn and the other leaves were falling. The leaf told me, “No. During the whole spring and summer I was completely alive. I worked hard to help nourish the tree, and now much of me is in the tree. I am not limited by this form. I am also the whole tree, and when I go back to the soil, I will continue to nourish the tree. So I don’t worry at all. As I leave this branch and float to the ground, I will wave to the tree and tell her, ‘I will see you again very soon.’

… That day there was a wind blowing and, after a while, I saw the leaf leave the branch and float down to the soil, dancing joyfully, because as it floated it saw itself already there in the tree. It was so happy. I bowed my head, knowing that I have a lot to learn from the leaf because it is not afraid-it knew nothing can be born and nothing can die.”

Cultural Beliefs About Trees

Trees are considered sacred in virtually every place where humans have settled.

There are many profound beliefs surrounding trees that people have held for millennia. Here are some interesting and touching examples:

  • For the Sng’oi people of Malaysia, a person and a tree can belong with each other, and this relationship is maintained for life. Certain trees and certain people belong together. When a person belongs with a tree, they also belong with its offspring: any trees that grow from the seeds of the first tree, no matter how far the seeds may scatter. The Sng’oi people call upon their intuition to know which child trees have sprung from which parent trees.
  • The World Tree is said to dwell in three worlds: Its roots reach down to the underworld, its trunk sits on the Earth, and its branches extend up to the heavens. Many cultures share a belief that this tree is the Axis Mundi or World Axis which supports or holds up the cosmos. For the Mayan peoples, the Axis Mundi was a massive Ceiba (in other cultures, it is called Kapok) tree that stands at the center of the world. The Mayan beliefs reflect that human souls first came into being as the sacred white flowers on the branches of the Ceiba tree. Souls of the dead Mayan ancestors rose from the roots of the Axis Mundi up through its branches and into the celestial realms.
  • In Germanic regions, it was believed that mankind was created from tree trunks, echoing the perception that people and trees have much in common.
  • In Sweden, some trees were considered “wardens” and could guard a home from bad luck. The warden was usually a very old tree growing on the lot near the home. The family living there had such great respect for the tree that they would often adopt a surname related to the name of the tree.
  • A well-known sacred tree in Norse mythology was Yggdrasil, a giant ash tree that was said to link and shelter the nine worlds that were believed to exist.
  • In Irish and English folklore, fairies would be found wherever Ash, Oak, and Hawthorne trees grew together. Hawthorn trees were regarded as a powerful symbol of protection, and were often planted near houses to ward off lightning as well as evil spirits. On the dawn of Beltane, it was believed that women who bathed in the dew from a Hawthorne blossom would become beautiful, and men who washed their hands in the dew would become skilled craftsmen.
  • Buddhists have a deep reverence for the Bodhi tree, a type of fig tree with heart-shaped leaves, beneath which the Buddha is said to have meditated for 49 days, trying to reconcile his mind to the fact that there was suffering in the world. On the 49th day, he stood and thanked the tree for providing shade for him, and in that instant he attained enlightenment. Today, in the same location where the Buddha is believed to have sat, there grows a descendant of that same Bodhi tree. Buddhist myths say that the tree will live there until the world is destroyed, and the place where it grows will be the last place to be destroyed and when the world is reborn, that site will be the first place to appear.
  • The villagers of Piplantri, in Rajasthan, India, celebrate the birth of each little girl by planting 111 trees in her honor. The entire village works together to plant and care for the trees. This tradition not only ensures that the environment will be able to support the increasing population of the village, but it has also brought harmony and a drop in crime to the village.
  • In Malaysia, people maintain a very intimate relationship with trees. “There is a practice of tree planting around houses to the extent that the walls and wooden structures are allowed to give way to the roots of creeping plants, purposely sown at the bases of these structures.” The graveyards in Malaysia are covered so thickly with trees that the entire grounds are cool and sheltered from the tropical sun. The trees are allowed to take root into the graves and it is said that the trees whisper prayers to the creator asking for forgiveness of past transgressions of those buried in that place.

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