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African Dorylus raid

The name army ant (or legionary ant or "Marabunta") is applied to over 200 ant species, in different lineages, due to their aggressive predatory foraging groups, known as "raids", in which huge numbers of ants forage simultaneously over a certain area, attacking prey en masse.

Another shared feature is that unlike most ant species, army ants do not construct permanent nests, and an army ant colony moves almost incessantly over the time it exists. All species are members of the true ant family Formicidae,^{[citation needed]} but there are several groups that have independently evolved the same basic behavioral and ecological syndrome. This syndrome is often referred to as "legionary behavior", and is an example of convergent evolution.^[1]

[edit] Usage and circumscription

Historically, "army ant" referre, in the broad sense, to various members of 5 different ant subfamilies: in two of these cases, the Ponerinae and Myrmicinae, it is only a few species and genera that exhibit legionary behavior; in the other three lineages, Ecitoninae, Dorylinae, and Leptanillinae, all of the constituent species are legionary. More recently, ant classifications now recognize an additional New World subfamily, Leptanilloidinae, which also consists of obligate legionary species, and thus is another group now included among the army ants.

A 2003 study of thirty species (by Sean Brady of Cornell University) indicates that the ecitonine and doryline army ants together formed a monophyletic group: all shared identical genetic markers that suggest a common ancestor. Brady concluded that these two groups are therefore a single lineage that evolved in the mid-Cretaceous period in Gondwana,^[2] and so the two subfamilies are now generally united into a single subfamily Ecitoninae, though this is still not universally recognized.^[3]

Accordingly, the army ants as presently recognized consist of the following genera:

Subfamily Ponerinae

• Leptogenys (some species)
• Onychomyrmex
• Simopelta

Subfamily Myrmicinae

• Pheidolegeton

Subfamily Leptanilloidinae

• Asphinctanilloides
• Leptanilloides

Subfamily Leptanillinae

• Anomalomyrma
• Leptanilla
• Phaulomyrma
• Protanilla
• Yavnella

Subfamily Ecitoninae

• Aenictus
• Cheliomyrmex
• Dorylus
• Eciton
• Labidus
• Neivamyrmex
• Nomamyrmex

[edit] Ecitoninae

A soldier of the New World army ant Eciton burchelli

Most New World army ants belong to the subfamily Ecitoninae, and this is the most commonly-known lineage, therefore bears special mention. This subfamily is further broken into two groups, the tribes Cheliomyrmecini and Ecitonini. The former contains only the genus Cheliomyrmex, and the tribe Ecitonini contains four genera, Neivamyrmex, Nomamyrmex, Labidus, and Eciton, the genus after which the group is named (Brady, 2003, = Ecitoninae Tree of Life). The genus Neivamyrmex is the largest of all army ant genera, containing some 120 species, all in the United States. The most predominant species of Eciton is Eciton burchellii, whose common name is "army ant" and which is considered to be the archetypal species.

The Old World army ants are divided between the two tribes Aenictini and Dorylini. The tribe Aenictini is made up of a single genus, Aenictus, that contains over 50 species of army ant. The tribe Dorylini contains the aggressive driver ants in the genus Dorylus. There are some 60 species known.

Army ant taxonomy remains ever-changing, and genetic analysis will continue to provide more information about the relatedness of the various species.

Army ants in the Peruvian jungle have been observed to cover about 2 acres (0.81 ha) and be able to form a hanging ball about 3 feet (0.91 m) in diameter.

[edit] In fiction

• Carl Stephenson's 1938 short story "Leiningen Versus the Ants" concerns a massive column of army ants that threatens a Brazilian plantation. The story was adapted for an episode of the radio series Escape in 1948 and as the motion picture The Naked Jungle in 1954.
• In the MacGyver episode Trumbo's World (Season 1 Episode 6), MacGyver assists a reclusive landowner in Brazil to defend his home from army ants (referred to in the show as soldier ants and Marabunda). The size of the ant swarm is described as being two miles wide and ten miles long. The ants kill several humans in the episode within minutes. They are eventually defeated by flooding the fields on Trumbo's land. Footage from The Naked Jungle is used.
• In The Poisonwood Bible by Barbara Kingsolver, a huge swarm of ants attacks the village where the main characters live. The villagers and missionaries all run to the river and escape the ants by boat; they later return to find food and livestock completely devoured, including a memorable description of little piles of chicken bones on the hens' nests. The episode is a decisive moment for the disabled character Adah, because her mother leaves her behind, rescuing her baby sister instead; it is implied that she could have been eaten by the ants.^[4]

[edit] See also

• Driver ant

[edit] References

[edit] Further reading

• Brady, S. (2003). Evolution of the army ant syndrome: the origin and long-term evolutionary stasis of a complex of behavioral and reproductive adaptations.. PNAS 100(11): 6575-6579. 
• Gotwald, W.H., Jr. (1995). Army ants: the biology of social predation. Ithaca, New York: Cornell University Press. ISBN 0-8014-9932-1. 
• Rice, Nathan H., and A. M. Hutson (2003). "Antbirds and Army-Ant Swarms". in Christopher Perrins (Ed.). Firefly Encyclopedia of Birds. Firefly Books. p. 449. ISBN 1-55297-777-3. 
• Wilson, Edward O, and Bert Hölldobler, (1990) The Ants (Pulitzer Prize)

[edit] External links

• A Comprehensive Ant Website
• Army Ants Plug Potholes, March 2009.
• Army ant research page: personal website on research and computer modeling of army ants
• Instinct to swarm