Ecitoninae, Formicidae, Hymenoptera, Insecta, Arthropoda, Animalia
Austin, Texas, USA to Costa Rica (Watkins 1977). In Costa Rica, known from Atlantic slope sites (including La Selva, Monteverde).
Identification (Watkins 1977)
For worker images, see the very similar Nomamyrmex esenbeckii crassicornis.
Worker: back of head with deep transverse groove (absent in hartigii); top of petiole longitudinally wrinkled (not wrinkled in hartigii); hind margin of mesonotum emarginate (as opposed to straight in crassicornis).
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 distinctly separated along the midline (continuous, at least posteriorly, in crassicornis); longitudinal rugae indistinct or absent on second gastric tergite except in sulcus at anterior edge (present in crassicornis).
Nomamyrmex esenbeckii wilsoni 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. wilsoni columns may be found day or 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.
I have once observed this subspecies with prey. A column was entering and issuing from fissures in a trail, carrying abundant larvae and pupae of Atta, including pupae of fairly large workers. Also see observations on subspecies crassicornis, which also occurs in Costa Rica and has been observed attacking Atta.
Kjetil Aasen, a student working at La Selva Biological Station during the summer of 1997, made the following observation of a Nomamyrmex raid on Atta cephalotes:
On the evening on my last day at La Selva, I went to take a look at the Atta cephalotes colony between the bridge and the library and I was surprised to find a fierce battle in progress. It was dark and it was raining and thousands of Atta soldiers and Nomamyrmex esenbeckii were fighting in the area surrounding the main entrances of the Atta nest. They were all emerging from two closely spaced nest entrances and most of the Nomamyrmex were in the mandibles of some large leafcutter. In most cases, the Nomamyrmex were caught by their antenna, but they still managed to sting Atta, and they seemed to be very good at this because there were many dead or dying leafcutters on the battlefield. I did not see many dead Nomamyrmex.
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.
John T. Longino, The Evergreen State College, Olympia WA 98505 USA.firstname.lastname@example.org
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