Subfamily Formicinae

Named for the ant genus Formica, this the classical Latin word for ant.

The unifying characteristic of members of this subfamily is the venom-delivery apparatus, composed of large venom gland and reservoir for production and retention of formic acid (unique to formicines), vestigial sting, and hypopygium modified into a nozzle-like acidopore (SEM) for delivery of formic acid.

Most genera found in much of Canada and all US states. Nylanderia is limited to the warmer parts of North America, Myrmecocystus is western, especially southwestern (and Mexican), and introduced Paratrechina and South American origin Brachymyrmex spp. of are subtropical/urban in USA.

Most in warm months only, but Prenolepis is active during cooler months, even estivating in the deep South.

Honeydew and extrafloral nectar are major components of the diet, but most are also effective predators and/or scavengers.

Most have "typical" ant pattern of claustral colony foundation by a single queen sealed into an incipient nest. But many in Lasius, Formica, Nylanderia have colony foundation dependent on invading a colony of a congener, and a few of these spend their whole lives as inquilines in nests of the host. Polyergus are obligate, permanent parasites of certain Formica. The latter two genera do not overwinter any brood in the nest, while the others usually carry diapausing young larvae through the winter.

Formicines retain some primitive features such as the presence of cocoons around pupae, the presence of ocelli in workers, and little tendency toward reduction of palp or antennal segmentation in most species, except subterranean groups. Extreme modification of mandibles from primitive form of toothed, triangular blade is rare, found only in Polyergus. On the other hand, some members show considerable evolutionary advancement in behaviors such as cleptergy ("slave-making") and other forms of social parasitism, and symbiosis with root-feeding homopterans. Finally, all formicines have a very reduced sting and enlarged venom reservoir, with the venom gland, specialized (uniquely among ants) for the production of formic acid. [source: wikipedia.org]

descriptive characteristics and classification (wikipedia.org)

Keys to US genera and southeastern species (Mississippi State University)