Army ant

All species are members of the true ant family, Formicidae, but several groups have independently evolved the same basic behavioural and ecological syndrome.

[3][n 1] Most New World army ants belong to the genera Cheliomyrmex, Neivamyrmex, Nomamyrmex, Labidus, and Eciton.

In 2003, though, genetic analysis of various species suggests that several of these groups evolved from a single common ancestor, which lived approximately 100 million years ago at the time of the separation of the continents of Africa and South America, while other army ant lineages (Leptanillinae, plus members of Ponerinae, Amblyoponinae, and Myrmicinae) are still considered to represent independent evolutionary events.

[3] Army ant taxonomy remains in flux, and genetic analysis will likely continue to provide more information about the relatedness of the various taxa.

[5] The queens of army ants are unique in that they do not have wings, have an enlarged gaster size and an extended cylindrical abdomen.

[5][10] The term "army ant syndrome" refers to behavioral and reproductive traits such as obligate collective foraging, nomadism and highly specialized queens that allow these organisms to become the most ferocious social hunters.

The constant traveling is due to the need to hunt large amounts of prey to feed its enormous colony population.

At the end of the stationary phase, both the pupae emerge from their cocoons (eclosion) and the next generation of eggs hatch so the colony has a new group of workers and larvae.

Army ant queens never have to leave the protection of the colony, where they mate with foreign incoming males which disperse on nuptial flights.

[6][15] Sometimes, the workers will backtrack along the paths of prior emigrations to search for a queen that has been lost or merge with a sister colony.

Workers in army ant species have a unique role in selecting both the queen and the male mate.

This suggests that if workers produced male offspring, they might be hatched out of sync with the queen's sexual brood and not likely to be successfully reared to adulthood.

Underground species prey primarily on ground-dwelling arthropods and their larvae, earthworms, and occasionally also the young of vertebrates, turtle eggs, or oily seeds.

Although small vertebrates that get caught in the raid will be killed, the jaws of the American Eciton are not suited to this type of prey, in contrast to the African Dorylus.

These undesired prey are simply left behind and consumed by scavengers or by the flies that accompany the ant swarm.

Only a few species hunt primarily on the surface of the earth; they seek their prey mainly in leaf litter and in low vegetation.

[22] While foraging, army ants cause many invertebrates to flee from their hiding places under leaves of the forest floor, under tree bark, and other such locations, thereby allowing predators to catch them more easily.

For example, in the tropical rainforests of Panama, swarms of army ants attract many species of birds to this feast of scrambling insects, spiders, scorpions, worms, and other animals.

[23] While focused on feeding on these invertebrates, birds at army-ant swarms typically allow very close approach by people – within 1–2 metres (3.3–6.6 ft) in many cases – often providing the best opportunities to see many of these species.

The members of the bivouac hold onto each other's legs and so build a sort of ball, which may look unstructured to a layman's eyes, but is actually a well-organized structure.

At the smallest disturbance, soldiers gather on the top surface of the bivouac, ready to defend the nest with powerful mandibles and (in the case of the Ecitoninae) stingers.

[26] Many species of army ants are widely considered to be keystone species[27] due to their important ecological role as arthropod predators [28] and due to their large number of vertebrate and invertebrate associates that rely on army ant colonies for nutrition or protection.

[34] While some guests follow the colony emigrations on foot,[35][36][31] many others are phoretically transported, for example by attaching themselves on army ant workers such as the histerid beetle Nymphister kronaueri.

[37] The Neotropical army ant Eciton burchellii has an estimated 350 to 500 animal associates, the most of any one species known to science.

[13] A 2003 study of thirty species (by Sean Brady of Cornell University) indicates that army ants of subfamilies Ecitoninae (South America), Dorylinae (Africa) and Aenictinae (Asia) together formed a monophyletic group, based on data from three molecular genes and one mitochondrial gene.

[39] However, the unification of these lineages means that the only subfamily that is composed solely of legionary species is Leptanillinae, as Dorylinae contains many non-legionary genera.