Ants of the subfamily Pseudomyrmecinae:
identification of Pseudomyrmex species

This page reports the results of ongoing work. A complete key to all Pseudomyrmex species (ca. 200 species) is not yet available. A series of regional and species group keys, both published and unpublished (provisional), is provided below. Please make use of the provisional keys and send me feedback!

To avoid the inadvertent emergence of nomina nuda in the literature, undescribed species are referred to using a code number (sp. PSW-xx) (e.g., Pseudomyrmex sp. PSW-06).

Characters

The worker and queen castes of Pseudomyrmex do not exhibit spectacular interspecific variation in body shape or integument sculpture (nor do the males, except that their genitalia often have species-specific structures). Many of the species differ by subtle contrasts in the shape of the petiole, relative size of the eyes, length of the legs, etc. Thus, accurate morphometric measurements are essential for reliable identification. Consult the preceding link for more details.

Other characters used frequently in the keys include features of the pilosity and pubescence, integument sculpture, body color, and the configuration of the frontoclypeal complex. The term "standing pilosity" refers to hairs (setae) forming an angle of 45 degrees or more with the body surface (Wilson, 1955). "Pubescence" refers to short hairs that are appressed to the body surface. The sculpture of the integument is best observed under a soft light (e.g., interpose a Mylar filter between the source of the illumination and the specimen). Terminology for surface sculpture follows Harris (1979). Some features of the morphology of the frontoclypeal complex (which encompasses the frontal carinae, antennal sclerites, and median clypeal lobe) are illustrated below:

Pseudomyrmex worker, frontoclypeal complex.

Identification options

First there is a tabular key to the nine major species groups of Pseudomyrmex established by Ward (1989). About 85% of all Pseudomyrmex species can be assigned to one of these species groups. Keys are now available for four of these species groups. Thus, if the tabular key suggests that you have a specimen belonging to one of the following groups, you can key it down to species.

• Pseudomyrmex ferrugineus group. See also the published key in Ward (1993).
• Pseudomyrmex oculatus group (under construction). See the published key in Ward (1989).
• Pseudomyrmex subtilissimus group (under construction). See the published key in Ward (1989).
• Pseudomyrmex viduus group. See also the published key in Ward (1999b).

Second, some of the above species group keys incorporate all the Pseudomyrmex species that have been found in association with particular specialized ant-plants (i.e., the keys include members of the named species group, plus other Pseudomyrmex species that have independently colonized the same kinds of ant-plants). In this way you should be able to identify any Pseudomyrmex species inhabiting:

• swollen-thorn acacias, use key to P. ferrugineus group.
• Triplaris (Polygonaceae), use key to P. viduus group.
• Tachigali (Fabaceae: Caesalpinoideae), use key to P. viduus group.

Third, I have developed regional keys. These attempt to permit the identification of all Pseudomyrmex species occurring in a given region. The Central American and West Indian keys are provisional in nature. A number of undescribed species are present.

• Key to the species of Nearctic Pseudomyrmex. See also Ward (1985).
• Key to the species of Costa Rican Pseudomyrmex. With illustrations: PDF version (requires Adobe Acrobat).
• Key to the species of Mexican and Central American Pseudomyrmex (under construction).
• Key to the Pseudomyrmex species of the West Indies (under construction).

Literature Cited

• Harris, R. A. 1979. A glossary of surface sculpturing. California Department of Food and Agriculture. Laboratory Services, Entomology. Occasional Papers 28:1-31.
• Ward, P. S. 1985. The Nearctic species of the genus Pseudomyrmex (Hymenoptera: Formicidae). Quaestiones Entomologicae 21:209-246.
• Ward, P.S. 1989. Systematic studies on pseudomyrmecine ants: revision of the Pseudomyrmex oculatus and P. subtilissimus species groups, with taxonomic comments on other species. Quaestiones Entomologicae 25:393-468.
• Ward, P. S. 1993. Systematic studies on Pseudomyrmex acacia-ants (Hymenoptera: Formicidae: Pseudomyrmecinae). Journal of Hymenoptera Research 2:117-168.
• Ward, P. S. 1999b. Systematics, biogeography and host plant associations of the Pseudomyrmex viduus group (Hymenoptera: Formicidae), Triplaris- and Tachigali-inhabiting ants. Zoological Journal of the Linnean Society 126:451-540.
• Wilson, E. O. 1955. A monographic revision of the ant genus Lasius. Bulletin of the Museum of Comparative Zoology 113:1-201.

Philip S. Ward Department of Entomology and Center for Population Biology University of California at Davis Davis, CA 95616, USA email: psward@ucdavis.edu

http://entomology.ucdavis.edu/faculty/ward/psintro.html last modified 22 October 2002