Ecitoninae, Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
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Additional images: worker petiole and postpetiole, lateral view (image); worker mesosoma, dorsal view (image).
For images of male, see the similar N. esenbeckii wilsoni.
Range
Costa Rica south to Amazon-Madeira-Mamore river system in Brazil and Bolivia. In Costa Rica, known from southern Pacific slope.
Identification
Worker: back of head with deep transverse groove (absent in hartigii); top of petiole longitudinally wrinkled (not wrinkled in hartigii); hind margin of mesonotum nearly straight (as opposed to emarginate in wilsoni).
Male: Border of head behind ocellar peduncle with a narrow lamella (absent in hartigii); first gastric tergite usually with longitudinal rugae; width of blade of stipes about one half its length (wider in hartigii); volsellae blunt, gradually tapered or snout-shaped; setae on fifth gastric tergite continuous across tergite, at least posteriorly (distinctly separated along the midline in wilsoni); longitudinal rugae present on second gastric tergite (indistinct or absent except in sulcus at anterior edge in wilsoni).
Natural History
Nomamyrmex esenbeckii crassicornis is in the tribe Ecitoninae, which are the New World army ants. It shares with all army ants the habits of group raiding and colony nomadism. Nomamyrmex esenbeckii crassicornis forages in columns during the day; I do not know if they forage at night. The workers are robust and their columns very conspicuous. The species is uncommon relative to several species of Eciton and Labidus.
Nomamyrmex esenbeckii sensu lato appears to be a specialist raider of Atta colonies (Swartz 1998 and included references). Swartz reviewed the earlier literature, in which workers reported Nomamyrmex raids on Atta colonies in Mexico and various sites in Brazil. She also observed and carefully documented a raid on an Atta cephalotes colony in Corcovado National Park, Costa Rica.
During work in Corcovado National Park in the early 1980's, I saw this subspecies twice with prey and three times in the process of raiding ant colonies. Four of these observations involved attines. I observed Atta brood as prey in one column, and Acromyrmex brood as prey in another. I observed two attacks on mature Atta cephalotes colonies. Both these raids were observed mid-morning. In the first instance, Nomamyrmex were entering through a collapsed Atta chamber in the middle of a trail, taking away brood. I saw very little response on the Atta's part. There were two dead soldiers near the raiding column. In the second case, Atta workers were abundant on the surface of their mound, and had brought piles of brood to the surface of the largest, most active mounds. Nomamyrmex columns were carrying adult Atta soldiers and brood down into Atta nest entrances, suggesting a largely subterranean raid. I observed one raid on a Pheidole nest.
See also esenbeckii wilsoni, which I have also observed with Attine prey. The two subspecies of esenbeckii are the only army ants I have observed preying upon mature Atta colonies.
Literature Cited
Swartz, M. B. 1998. Predation on an Atta cephalotes colony by an army ant, Nomamyrmex esenbeckii. Biotropica 30:682-684.
Watkins, J. F. II 1977. The species and subspecies of Nomamyrmex (Dorylinae: Formicidae). Journal of the Kansas Entomological Society 50:203-214.
Page author:
John T. Longino, The Evergreen State College, Olympia WA 98505 USA.longinoj@evergreen.edu
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