Described as 'hyperdiverse', the genus Pheidole probably contains up to 1500 species worldwide (about 900 are currently known, but new species are constantly being discovered). The number of species in the Western Hemisphere (New World) currently stands at over 600, with over 70 recognized species in the U.S. This number is also climbing, and it is estimated that the actual number of Pheidole species in North America, north of Mexico, is around 100. Pheidole species are often referred to as 'big-headed ants'.
These ants are found in a wide array of habitats, including deserts, grasslands, tropical rainforests, and temperate woodlands.
In most species, the workers are dimorphic - with tiny, slender 'minors', and much larger 'majors' with disproportionately large heads. Six New World species are trimorphic, and posses a third (and larger) worker caste; the 'supermajor' (see the Pheidole obtusospinosa images for more info). In Pheidole colonies, the large and powerful majors often accompany the smaller minor workers on foraging forays, most often probably serving as a defensive escort, but also assisting with large food items. They also play a critical role as defenders of the nest itself. In many species, the majors with their powerful mandibles, also process or 'mill' large seeds that have been harvested, and brought back to the nest.
Most Pheidole species are omnivores, gathering seeds/plant matter, and scavenging or preying upon insects and other arthropods- though some rely primarily on harvested seeds.
Pheidole ants are part of the subfamily Myrmicinae, which is the largest subfamily of ants (Hymenoptera: Formicidae) in the world. [scroll down for additional notes/references]
·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
·Huang, M. 2010. Multi-Phase Defense by the Big-Headed Ant, Pheidole obtusospinosa, Against Raiding Army Ants. Journal of Insect Science, 10(1):1-10. 2010.
·Johnson, R.A. 2000. Seed Harvesting Ants (Hymenoptera: Formicidae) of North America: An Overview of Ecology and Biogeography. Sociobiology Vol.36, No. 1, 2000
·Wilson, E.O. 2003. Pheidole in the New World: A Dominant Hyperdiverse Ant Genus. Harvard University Press, Cambridge, Massachusetts