Pheidole is currently the most species rich genus of ants in the world, with many species still awaiting description (Moreau, 2008).
With a worldwide distribution, the "hyperdiverse" myrmicine genus Pheidole is unsurpassed for number of species in a single ant genus (Wilson, 2003). Pheidole presently comprises more than 9.5 percent of the entire known world ant fauna with over 1,100 species described worldwide (Bolton et al., 2007). The 600+ described species of Pheidole in the New World were recently the subject of a major revision by E. O. Wilson (2003) that included species descriptions and detailed morphological drawings of each species.
Ants in the genus Pheidole possess a dimorphic worker caste that is comprised of a minor worker subcaste and major worker subcaste, with these big-headed major workers sometimes referred to as soldiers. All known species of Pheidole are dimorphic - except six species of workerless social parasites and at least eight species possess an unusually large super major subcaste in addition to the typical minor and major subcastes (trimorphic worker caste), with minor workers performing most of the tasks within the nest and foraging, and large-headed majors specializing on colony defense and/or food processing. A large number of Pheidole major workers are also known to be involved in the milling of seeds harvested by the minor and major worker caste, and these seeds are often stored in granaries within the ant nest. The evolution of worker polymorphism in ants has been hypothesized to be associated with a dietary change (Wilson, 1984; Hölldobler & Wilson, 1990; Ferster et al., 2006; Powell & Franks, 2006).
Additionally ants in Pheidole exhibit reduction of the sting in both the major and minor caste without an increase in defensive secretions. Defense of the colony and food sources are executed by cooperative fighting, instead of a “sting”. Group retrieval of prey items is often accomplished by “spread-eagling” the prey or intruder.
The earliest confirmed fossil specimens of Pheidole are found in the Florissant shales of Colorado, which is late Eocene, ~34 million years ago (Ma) in age (Carpenter, 1930).
PheidoleHNS , Westw. Ann. & Mag. Nat. Hist. vi. 8/ (1841). OecophthoraHNS , Heer, Ueber die Hausameise Madeir. (1852).
Head large in the worker major, of moderate size in the other sexes. Mandibles very strong, the inner edge oblique, without teeth in the large worker, toothed in the small worker. Maxil- lary palpi 2-jointed; labial palpi 2-jointed. Antennae 12-jointed in the females, large and small workers. Thorax narrower than the head, much more so in the large workers. Wings with two complete submarginal cells, and one complete discoidal cell; the metathorax usually with two short spines. The anterior tibias in the females, large and small workers, with a pectinate spine at their apex.
We have compared numerous examples of OecophthoraHNS with specimens of Pheidole providensHNS , and cannot find the differences mentioned by Professor Heer; there is no difference in the relative length of the first joint of the tarsus; the mandibles are equally acute at their apex; in all generic characters they pre- cisely correspond. We have not seen the males of either of the types, but as other sexes agree in every particular, we have in- cluded in one genus all such species as possess the characters above given.
Une desailee, peut-etre nouvelle, mais sans certitude, car les reines des petits PheidoleHNS sont tres peu decrites. Ziela, savane (LaMOTTE). Se placerait entre corticicolaHNS SANT., (espece commune au Banco) et decarinataHNS SANT. du Soudan. A revoir quand les ouvrieres seront prises. Cette Fourmi est remarquablement petite pour une reine (4 mm. 8).
Des soldats de Ziela, Keoulenta, 6 ailees et 10 ouvrieres du Mont To a 1.600 m., sont laisses de cote provisoirement. Ils sont peut-etre nouveaux, mais ni la bibliographie ni les collections suisses consultees n'apportent de certitude a cet egard, tant la systematique du genre est incertaine.