Members of this subfamily are known as army ants and are sometimes referred to as legionary ants. This New World subfamily has about 170 species in 5 genera and is dominated by the large genus, Neivamyrmex. The Nearctic region is home to about 30 species in three genera with the vast majority of species in genus Neivamyrmex. They can be found throughout northern Mexico and southern USA with a northward extension in the Mississippi River valley.
Army ants are predaceous and are known for their foraging expeditions the size of which are sometimes exaggerated. Army ants exhibit a number of morphological and biological peculiarities not common to most ants such as wasp like males, wingless termite like females, blind workers, and their raiding and emigrating behavior. Rettenmeyer (1963) outlined the following traits in which they differ from other ants: (1) They feed almost exclusively on animal prey which is collected by large groups of raiding workers; (2) their raiding columns usually connect to the nest by at least one continuous column; (3) the entire colony periodically and frequently emigrates to new nest sites; (4) emigrations are largely dependent on the size, caste, age, and range of ages of the brood (or broods); and (5) the colonies are founded by division of an entire colony into two (or possibly several) daughter colonies. Other ants may possess some of these traits, but not all of them (Smith, D.R. 1979: 1326). Group raiding allows army ants to exploit food sources unavailable to other ants: large arthropods and the brood of other social insects. These prey are not normally accessible to ants foraging individually or in small groups, but they can be overcome when swarmed by large numbers of attackers.
Much of the biological work on army ants has been done in Central America on the terrestrial species of Eciton which bivouac in large clusters above the ground and whose colonies may number up to a million individuals. Most of the army ants, however, are subterranean in habit, though the raiding columns of some may appear above ground. Raiding may be in columns only several ants wide or in swarms of a fan shaped pattern. Most of the prey is other Arthropods, only occasionally vertebrates. All species have nomadic and statary activity cycles where the entire colony moves from one area to another, a unique behavior studied by Schneirla and Rettenmeyer in the papers listed below (Smith, D.R. 1979: 1326).
The army ants are currently being revised by Snelling. See www.armyants.org for more details.
Ecitoninae is a monophyletic subfamily (Bolton, 1990e and confirmed in subsequent phylogenetic studies by Baroni Urbani, Bolton & Ward, 1992 and Grimaldi, Agosti & Carpenter, 1997. Am. Mus. Nov. 3208). It is defined by the following synapomorphies:
Worker:
Male:
Recognition. Antenna 12–segmented. Antennal sockets located close to each other and very close to the anterior margin of the head; the clypeus is reduced to a very narrow band in front of them. Frontal carinae not expanded laterally into frontal lobes so that the antennal sockets are completely visible in full face view. Eye with either a single facet or absent. Propodeum without spines or angles. Mesosoma separated from gaster by two segments, the petiole and postpetiole. Pygidium without teeth.
Similar Subfamilies. The reduced clypeus, small eye, and exposed antennal sockets are similar to subfamily Cerapachyinae. The teeth on the pygidium clearly distinguish Cerapachyinae. However, in California, Cerapachyinae workers (genus Cerapachys) have been taken as they were walking with a column of army ants (Neivamyrmex sp.) so collections of army ants should be carefully examined for the rare Cerapachys (Snelling, Cover & Fisher).
Nearctic Genera. Labidus, Neivamyrmex, Nomamyrmex
Non-Nearctic Genera. Cheliomyrmex, Eciton
Included Tribes.
Literature Overview. Chapter 16 in Hölldobler & Wilson, 1990 is an excellent quick introduction to army ant biology. Much more detail can be found in the excellent books on army ants by Gotwald, 1995 (Army ants: the biology of social predation, Cornell U. Press) and Schneirla, 1971 (Army ants. A study in social organization (edited by H.R. Topoff)).
Revision. Smith, M.R. 1942c: 537-590 (USA). || Borgmeier, 1955: 1-716 (New World).||Watkins, 1976: 1-102 (keys to genera and species of w. and m., distribution).
Taxonomy. Wheeler, G.C. 1943: 319-332 (larva).|| Borgmeier, 1953: 1-51.|| Borgmeier, 1958a: 197-208 (identification of q. to genus).|| Wheeler, G.C. & Wheeler, J. 1964c: 129-137 (larva). || Watkins, 1972: 347-372 (USANeivamyrmex). || Watkins, 1985: 479-502 (keys to USA species for w.m., distribution).