Pogonomyrmex maricopa worker.

The workers of P. maricopa can be quite variable in their appearance. This can make them difficult to identify - especially in areas where the range of this ant coincides with that of the very similar Pogonomyrmex californicus.

Typical length of worker ranges from 6.0mm to 9.0mm [Taber 1998], and typical coloration ranges from light red, to deep red. This species sometimes possesses propodeal spines of variable lengths, but more frequently lacks them.

The external nest structures constructed by these ants are also highly variable, consisting of sand or gravel craters, large sand mounds with apical depressions (covered with gravel), or even fine sand mounds with cemented calcium carbonate caps. A nest we observed south of Tucson consisted of nothing more than an unadorned entrance hole, and would have gone unnoticed but for the workers entering and exiting.

Pogonomyrmex maricopa is famous for having what is usually cited as the most toxic insect venom known [1].

The US range of this ant includes parts of the following states: Arizona, California, Colorado, New Mexico, Nevada, Texas and Utah. Its range in Mexico includes parts of Baja California, Chihuahua, Sinaloa and Sonora.

[IMAGE: Pogonomyrmex maricopa worker, Arizona USA] [scroll down for additional notes/references]

ADDITIONAL NOTES/REFERENCES:

[1] A venom's toxicity is usually measured by its LD50 value (a lower LD50 value indicates a potentially more toxic/lethal venom). The LD50 for Pogonomyrmex maricopa is .12 mg / kg - making this venom lethal enough to kill a mouse with a few stings, or a 2 kg / 4.4 lb rat with just 12 stings. P.maricopa is usually cited as having the most powerful venom in the insect world. Other Pogo species do not have venoms quite as potent as P.maricopa's, but even an average Pogo venom is much more toxic than that of a yellowjacket (Vespula squamosa) or a paper wasp (Polistes canadensis). The LD50 values for the above mentioned insects are 3.5 mg / kg, and 2.4 mg / kg, respectively, and in one study, an average value for 10 Pogo species was determined to be .66 mg / kg.The amount of venom injected by a Pogo with each sting is so small, however, that most humans and other large animals are not in danger of dying from a Pogo attack (though it is an extremely painful deterrent). Human deaths occasionally do result - but this is usually due to an anaphylactic (severe allergic) reaction to being stung.

·Cole, A.C. 1968. Pogonomyrmex Harvester Ants: A Study of the Genus in North America. Knoxville, University of Tennessee Press
·Johnson, R.A. 2000. Seed Harvesting Ants (Hymenoptera: Formicidae) of North America: An Overview of Ecology and Biogeography. Sociobiology Vol.36, No. 1, 2000
·Klotz, J.H., Schmidt, J.O., Pinnas, J.L., & Klotz, S.A. 2005. Consequences of Harvester Ant Incursion into Urbanized Areas: A Case History of Sting Anaphylaxis. Socialbiology Vol. 45, No. 3, 2005
·Meyer, W.L. 1996. University of Florida Book of Insect Records, Chapter 23, Most Toxic Insect Venom. Dept. of Entomology & Nematology University of Florida, Gainesville, FL 32611, May 1996
·Taber, S.W. 1998. The World of the Harvester Ants. College Station, TX, Texas A&M University Press