This subfamily is the predominant group of ants in North America. They are most common in the north and in the mountains with their numbers decreasing rapidly toward the southern part of the United States (Smith, D.R. 1979: 1422). Worldwide, Formicinae has about 3700 species in 49 genera (Shattuck, 1999. Australian Ants: 86). The Nearctic region has 230 species and subspecies placed in 11 genera.
Subfamily Formicinae is a monophyletic group with the following autapomorphies (Agosti, 1991: 293-294; Shattuck, 1992b: 203; Grimaldi & Agosti, 2000. Proc. Nat. Acad. Sci. 97: 13678):
Together, subfamilies Dolichoderinae, Formicinae and Aneuretinae (represented by a single species found only in Sri Lanka) also form a monophyletic group. These three subfamilies are believed to have split off very early in evolutionary history from the lineage of the remainder of the ants. This split is estimated to have occurred about 100 million years ago (Grimaldi & Agosti, 2000: fig. 2).
Recognition. The mesosoma is attached to the gaster by a single segment, the petiole. The gaster does not have constrictions between between segments. The sting is absent, and the tip of the gaster has a small circular opening (the acidopore) that is usually surrounded by a ring of short hairs.
Similar Subfamilies. Species of Formicinae are most commonly confused with species of Dolichoderinae since both subfamilies have the mesosoma attached to the gaster by a single segment, lack a sting, and often are of similar overall size and shape. However, formicines can always be separated from dolichoderines by the tip of the gaster; in formicines there is a small circular opening (most easily seen by the ring of hairs surrounding it) while all dolichoderines have a slit-like opening. Species of Ponerinae also have the mesosoma attached to the gaster by a single segment, but they are less likely to be confused with formicines since ponerines are generally smaller than formicines. Ponerines can be separated from all formicines by the lack of an acidopore. Many ponerines have a well developed sting (absent in formicines) and most have a constriction between the first and second gastral segments.
Nearctic Genera. Acropyga, Brachymyrmex , Camponotus, Formica, Lasius, Myrmelachista, Myrmecocystus, Paratrechina, Plagiolepis, Polyergus, Prenolepis
Non-Nearctic Genera. Agraulomyrmex, Alloformica, Anoplolepis, Aphomomyrmex, Bajcaridris, Bregmatomyrma, Calomyrmex, Cataglyphis, Cladomyrma, Echinopla, Euprenolepis, Forelophilus, Gesomyrmex, Gigantiops, Lasiophanes, Lepisiota, Melophorus, Myrmecorhynchus, Myrmoteras, Notoncus, Notostigma, Oecophylla, Opisthopsis, Overbeckia, Petalomyrmex, Phasmomyrmex, Polyrhachis, Proformica, Prolasius, Pseudaphomomyrmex, Pseudolasius, Pseudonotoncus, Rossomyrmex, Santschiella, Stigmacros, Teratomyrmex
Tribes. The tribal structure of Formicinae is not well understood. Hölldobler & Wilson, 1990 divided the subfamily into 13 tribes but did not provide diagnostic characters. Agosti, 1991 divided formicine genera into four groups based on the position of the coxae, petiole and helcium (presclerites of the first gastral segment that attach to the petiole). Work remains to be done before an accepted tribal structure is established. Below is the tribal assignments from Bolton, 1995b.