Marginalia Insecta, 2007, Volume 2: 2

Observations of Neivamyrmex fallax Borgmier and Solenopsis xyloni McCook (Hymenoptera: Formicidae) [pdf]

JoVonn G. Hill
Mississippi Entomological Museum
Box 9775
Mississippi State University, MS 39762


            Species in the genus Neivamyrmex Borgmeier (Hymenoptera: Formicidae: Ecitoninae) are commonly referred to as army ants.  These species feed almost exclusively on animal prey, typically the brood of other ant species.  Army ants do not have a permanent nest site, but instead are nomadic in nature, with the entire colony periodically moving to a new temporary nest site, also called a biovouac.  The habits of many army ant species are not well known as they seem to avoid direct sunlight or are primarily subterranean in nature.  However, the raids and migrations of several, species such as N. californicus Mayr, N harrisi Haldeman, N. nigrescens Cresson, N. opacithorax (Emery), N. pilosus (Smith), and, N. texanus Watkins, often take place above ground (Watkins, 1985).  Neivamyrmex fallax Borgmeier, a species upon which little is known, was first described in 1953 from a series of specimens from Texas and Louisiana (Borgmeier, 1953).  Since then, this species has been reported from Guatemala and Mexico, and in the United States from Arizona, Kansas, and New Mexico (Watkins, 1985). 


            On 27 June 2006, while on a collecting trip in west Texas, a colony of N. fallax was observed raiding a colony of Solenopsis xyloni McCook.  These observations were made just outside of Alpine, in Brewster County, Texas (30°20’46”N 103°41’39”W) at 1,548 m, behind a pavilion along a fencerow separating a hotel parking lot and a pasture. The activity occurred in an area measuring approximately 1x1.5 m that consisted of mostly bare soil and gravel with some forbs andCynodon dactylon (L,) Pers (Poaceae) (Bermuda grass).  The observations were made between 7:55 P.M.-9:10 P.M., and the temperature was 28.8°C.
            While collections of ants were being made in the area, a large number of S. xyloni were observed, apparently relocating their colony from an old nest site to a new one approximately one meter away.  Many N. fallax workers were emerging from three holes in the ground between these two locations, whereupon they attacked the S. xyloni workers and took their brood (eggs and pupa).  In most cases, the S. xyloni workers only minimally defended their brood, before dropping it and running away.  In other cases, the N. fallax took the brood from the mandibles of the S. xyloni workers after a brief skirmish.  Several S. xyloni workers carrying brood apparently tried to evade the onslaught of their attackers by climbing onto a small forb.  When a N. fallax worker ventured up the forb, the S. xyloni moved further up the plant until they were at the top.  When the N. fallax neared them, the Solenopsis dropped their brood, and fell to the ground.  The N. fallax workers also were observed also attacking male and female S. xyloni alates and carrying them underground after they were subdued.  One S. xyloni worker also was observed being carried underground.  Additionally, several N. fallax workers were seen entering and exiting the S. xyloni colony, but none of those exiting were observed carrying anything.         
            During the course of these observations, the movement trail of the Solenopsis became more obtuse as the Neivamyrmex pushed further into their ranks.  A couple of workers of two other ant species, Pogonomyrmex rugosus Emery and Aphaenogaster cockerelli André, were also moving throughout the area.  The S. xyloni attacked both of these larger species when encountering them with seemingly greater aggressiveness than they exhibited for the more similar sized N. fallax, and in one case were able to kill one of the P. rugosus workers. 
            The observations ceased near sundown. The next morning the site was visited again, but there was no sign of either the Neivamyrmex or the Solenopsis.  It would be interesting to know whether the Solenopsis were already moving their colony at the time and the Neivamyrmex took advantage of their vulnerability, or if the Solenopsis were moving because the Neivamyrmex already had attacked their original colony.


Funding for this project was provided in part by the William. H. Cross Memorial Fund. 

Literature Cited

Borgmeier, T.  1953. Vorarbeiten zu einer Revision der Neotropischen Wanderameisen. Studia Entomologica 2: 1-51.

Smith, D. R. 1979.  Superfamily Formicoidea [pp.1323-1467]. In Krombein, K. V., P. D. Hurd Jr., D. R. Smith, and B. D. Burks (eds.),  Catalog of Hymenoptera in America north of Mexico, Vol. 2: Apocrita (Aculeata).  Smithsonian Institution Press, Washington D.C. xvi + pp. 1199-2209.

Watkins, J. F. 1985. The identification and distribution of the army ants of the United States of America (Hymenoptera: Formicidae: Ecitoninae). Journal of the Kansas Entomological Society 58: 479-502.


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