Acromyrmex versicolor worker.

Acromyrmex versicolor is the only member of this genus (Acromyrmex) found in the U.S. It is commonly seen in Sonoran Desert regions of Arizona, and in parts of Texas and California. Acromyrmex ants are found only in subtropical and tropical areas of the New World.

Like other members of the tribe Attini (a group of ants within the subfamily Myrmicinae - all known as 'leafcutters'), A. versicolor cultivates a symbiotic fungus on cut and masticated leaf/plant fragments. This fungus serves as the primary food source for the larvae, and other colony members that remain in the nest. In addition to fungus, the queen also consumes inviable 'trophic' eggs laid by workers. The foraging workers engaged in leaf cutting and gathering outside of the nest probably receive the bulk of their nourishment from saps that are ingested during these plant-cutting activities.

These ants can harvest huge amounts of foliage, from a wide variety of plant species.

Acromyrmex ants are polymorphic, with workers of different sizes and proportions engaged in specialized tasks within the colony. Generally, smaller workers tend the fungus gardens and developing brood within the nest. Among other tasks, the larger workers forage for plant material and perform nest maintenance/construction. Both major and minor workers actively protect the colony's fungus gardens from contamination by outside pathogens and destructive fungal parasites.

A. versicolor is a true desert ant, and nests in the ground - usually in the shade, or partial shade of adult trees. The external nest structures (made of sand and gravel) are often up to 30 cm / 1 foot tall, and resemble tiny volcanoes. Because of this, these ants are sometimes referred to locally as 'volcano ants'.

In the majority of cases, A. versicolor colonies are founded cooperatively by multiple queens (pleometrosis), though all but one are eventually killed off during the early stages of colony development.

[IMAGE: Acromymex versicolor worker in southern Arizona USA [scroll down for additional note/references]

References for entire page :

·Fisher, B.L. & S.P. Cover. 2007. Ants of North America: A Guide to the Genera. Berkeley and Los Angeles, CA, University of California Press
·Hölldobler, B. & E.O. Wilson.1990. The Ants. Cambridge, MA, Belknap/Harvard Press

·Hölldobler, B. & E.O. Wilson. 2011. The Leafcutter Ants; Civilization by Instinct. W.W. Norton & Company, New York & London
·Hughes, O.H., S. Sumner, S. Van Borm, & J.J. Boomsma. 2003. Worker Caste Polymorphism has a Genetic Basis in Acromyrmex Leaf-Cutting Ants. Proc Nat'l Acad Sci, 2003, 100(16): 9394-9397
·Rissing, S.W, R.A. Johnson & G.B. Pollock. 1986. Natal Nest Distribution and Pleometrosis in the Desert Leaf-Cutting Ant Acromyrmex Versicolor (Pergande) (Hymenoptera: Formicidae). Psyche Volume 93 (1986), Issue 3-4, pp. 177-186