Army ant

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 all 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, 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.

Usage, circumscription

Historically, "army ant" referred, 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 [ [http://news.bbc.co.uk/2/hi/science/nature/3014011.stm BBC News, Dr. David Whitehouse, "Ant history revealed"] 10 May 2003.] , and so the two subfamilies are now generally united into a single subfamily Ecitoninae, though this is still not universally recognized (e.g. [Engel, M.S., Grimaldi, D.A. 2005. Primitive new ants in Cretaceous amber from Myanmar, New Jersey, and Canada (Hymenoptera: Formicidae). American Museum Novitates 3485: 1–24.] ).

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"

Ecitoninae

* 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, [http://tolweb.org/tree?group=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.

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). The size of the ant swarm is described as being several miles long and wide. The ants kill several humans in the episode within minutes of being swarmed. They are eventually defeated by flooding the fields on Trumbo's land.

In "Indiana Jones and the Kingdom of the Crystal Skull", a legion of siafu eat several Soviet soldiers alive, despite this behaviour not being present in reality. Additionally, Siafu are native to Africa and Asia, and are absent from the film's South American setting (although similar species exist there).

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. [http://www.sparknotes.com/lit/poisonwood/section9.rhtml]

Notes

External links

* [http://www.antweb.org/ A Comprehensive Ant Website] Personal website on research and computer modeling of army ants (with video and images):
* [http://www.infiniteworld.org/research/introduction.htm Army ant research page]
* [http://www.nytimes.com/2007/11/13/science/13traff.html?ex=1352610000&en=e5a43463a82e710f&ei=5090&partner=rssuserland&emc=rss Instinct to swarm]

References and further reading

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