Aenictus

Aenictus occurs throughout Africa and in tropical and subtropical areas from India east through southern China to Taiwan and south to Australia with outlier, temperate-climate species or populations in Japan, Afghanistan, Armenia and south-central Australia (Bolton et al., 2006; Gotwald, 1995; Shattuck, 1999, 2008). While widespread, nowhere are they common. All known species are "army ants" and conduct raids using large numbers of workers, primarily attacking other ants, social wasps and termites. While there are reports of these ants preying on other insects and even collecting honeydew from homopterans (Santschi, 1933; Gotwald, 1995), these habits appear to be uncommon.

Foraging raids undertaken by these ants occur both day and night, usually across the ground surface but occasionally also arboreally. During raids, numerous workers attack a single nest or small area, with several workers coordinating their efforts to carry large prey items back to the nest or bivouac. They also have a nomadic life style, alternating between a migratory phase in which nests are temporary bivouacs in sheltered places above the ground and a stationary phase where semi-permanent underground nests are formed. During the nomadic phase bivouacs move regularly, sometimes more than once a day when larvae require large amounts of food. Individual nests usually contain up to several thousand workers, although nest fragments containing only a few hundred workers are often encountered. Queens are highly specialised and look less like workers than in most ant species. They have greatly enlarged gasters and are termed dichthadiform. New colonies are formed by the division of existing colonies rather than by individual queens as in most ant species.

Aenictus is the only extant genus in the subfamily Aenictinae. It contains valid species and subspecies. The phylogenetic relationship of Aenictus to other ants has been investigated by Bolton (1990), Baroni Urbani et al. (1992), Brady (2003), Brady and Ward (2005), Brady et al. (2006), and Moreau et al. (2006).

Identification
Workers of Aenictus may be separated from other ants by their moderately small size (less than about 4 mm), lack of eyes, long slender bodies and long legs. They are superficially similar to some myrmicines but differ in lacking the frontal lobes and in having the antennal sockets completely visible when viewed from the front (myrmicines have frontal lobes that are expanded towards the sides of the head and partly cover the antennal sockets). Some of the smaller, paler species are also similar to Leptanilla workers, but differ in being larger and only ten segments in the antennae rather than 12, and lacking a flexible promesonotal suture.

Males of Aenictus can be separated from those of other ants by the exposed antennal sockets and lack of a postpetiole, i.e., the gaster is smooth and lacks a constriction between the first and second segments. There are dozens of Aenictus species that have been described from males only. It is at difficult to match such forms to their workers without collecting from a live colony that contains males. Such collections are atypical for many Aenictus ants hence recent taxonomic practice has been to place unassociated males, and these male-only based names, beyond the scope of revisionary work being completed.

Identification Keys
Australia

Jaitrong and Hashimoto (2011, 2012) created species groups, based on worker morphology, in order to make it more manageable to make species determinations.


 * Key to Aenictus species groups
 * Aenictus species groups (diagnoses)

Nomenclature

 *  AENICTUS [Aenictinae]
 * Aenictus Shuckard, 1840b: 266. Type-species: Aenictus ambiguus, by original designation.
 * Aenictus senior synonym of Typhlatta: Forel, 1890b: ciii.
 * Aenictus senior synonym of Paraenictus: Wilson, 1964: 444.
 *  ENICTUS [unavailable name]
 * Enictus Walker, 1860: 306; Smith, F. 1865: 79; incorrect subsequent spellings of Aenictus: Bolton, 1995b: 19.
 * PARAENICTUS [junior synonym of Aenictus]
 * Paraenictus Wheeler, W.M. 1929g: 27 [as subgenus of Aenictus]. Type-species: Aenictus (Paraenictus) silvestrii, by monotypy.
 * Paraenictus junior synonym of Aenictus: Wilson, 1964: 444.
 * TYPHLATTA [junior synonym of Aenictus]
 * Typhlatta Smith, F. 1857a: 79. Type-species: Typhlatta laeviceps, by monotypy.
 * Typhlatta junior synonym of Aenictus: Forel, 1890b: ciii.
 * Typhlatta revived from synonymy as subgenus of Aenictus: Wheeler, W.M. 1930g: 198.
 * Typhlatta junior synonym of Aenictus: Wilson, 1964: 444.

Additional References

 * Baroni Urbani, C., Bolton, B. & Ward, P.S. (1992) The internal phylogeny of ants (Hymenoptera: Formicidae). Systematic Entomology, 17, 301–329.


 * Bolton, B. (1990) Army ants reassessed: the phylogeny and classification of the doryline section (Hymenoptera, Formicidae). Journal of Natural History, 24, 1339–1364.


 * Bolton, B. (1995) A new general catalogue of the ants of the world. Harvard University Press, Cambridge, Massachusetts, 504 pp.


 * Bolton, B., Alpert, G., Ward, P.S. & Naskrecki, P. (2006) Bolton’s Catalogue of Ants of the World: 1758–2005. Harvard University Press, Cambridge, Massachusetts (CD-ROM).


 * Brady, S.G. (2003) Evolution of the army ant syndrome: the origin and long-term evolutionary stasis of a complex of behavioral and reproductive adaptations. Proceedings of the National Academy of Sciences (USA), 100, 6575–6579.


 * Brady, S.G. & Ward, P.S. (2005) Morphological phylogeny of army ants and other dorylomorphs (Hymenoptera: Formicidae). Systematic Entomology, 30, 593–618.


 * Brady, S.G., Schultz, T.R., Fisher, B.L. & Ward, P.S. (2006) Evaluating alternative hypotheses for the early evolution and diversification of ants. Proceedings of the National Academy of Sciences (USA), 28, 18172–18177.


 * Disney, R.H.L. & Kistner, D.H. (1991) A new genus of Australasian/Oriental Phoridae associated with driver ants (Diptera; Hymenoptera, Formicidae). Sociobiology, 18, 269–281.


 * Gotwald, W.H. (1995) Army ants: the biology of social predation. Cornell University Press, Ithaca and London, 320 pp.


 * Jaitrong, W. & Yamane, S. 2011. Synopsis of Aenictus species groups and revision of the A. currax and A. laeviceps groups in the eastern Oriental, Indo-Australian, and Australasian regions (Hymenoptera: Formicidae: Aenictinae). Zootaxa, 3128, 1–46.


 * Jaitrong, W. & Hashimoto, Y. 2012. Revision of the Aenictus minutulus species group (Hymenoptera Formicidae Aenictinae) from Southeast Asia. Zootaxa 3426, 29-44.


 * Moreau, C.S., Bell, C.D., Vila, R., Archibald, S.B. & Pierce, N.E. (2006) Phylogeny of the ants: Diversification in the age of angiosperms. Science, 312, 101–104.


 * Santschi, F. (1933) Contribution à l'étude des fourmis de l'Afrique tropicale. Bulletin et Annales de la Société Entomologique de Belgique, 73, 95–108.


 * Shattuck, S.O. (1999) Australian Ants: Their biology and identification. Monographs in Invertebrate Taxonomy, 3, 1–226.


 * Shattuck, S.O. (2008) Review of the ant genus Aenictus (Hymenoptera: Formicidae) in Australia with notes on A. ceylonicus (Mayr). Zootaxa 1926, 1–19.


 * Schneirla, T.C. (1971) Army ants. A study in social organization. W. H. Freeman & Co., San Francisco, 349 pp.


 * Wheeler, W. M. (1930) Philippine ants of the genus Aenictus with descriptions of the females of two species. Journal of the New York Entomological Society, 38, 193–212.


 * Wilson, E.O. (1964) The true army ants of the Indo-Australian area. Pacific Insects, 6, 427–483.