A large and difficult genus of mostly hypogaeic ants; usually with very small, pale workers and much larger and dark-colored females and males.
The workers are usually monomorphic but in a few species, such as punctaticeps Mayr , saevissima (Smith) and geminata (Fabricius) , distinctly polymorphic. Antennae 10-jointed, first funicular joint large, club large, distinctly 2-jointed, the last joint very long. Mandibles narrow, with few (usually 4) teeth. Clypeus raised in the middle and projecting anteriorly, with two diverging ridges, or carinae, each in all but a few species terminating anteriorly in a strong tooth flanked by a smaller tooth on the side. Frontal carinae short, somewhat diverging behind. Eyes small, often minute or vestigial; ocelli very rarely present. Promesonotal suture indistinct, mesoepinotal suture well developed. Thorax more or less impressed at the latter. Epinotum always unarmed. Petiole with short peduncle and high, rounded node; postpetiole rounded, much lower than the petiolar node.
The female has 11-jointed (rarely 10-jointed) antennae and moderately large eyes and ocelli. Fore wings with one cubital and one discoidal cell; radial cell open.
The male is somewhat smaller than the female, with 12-jointed antennae. Scape very short, first funicular joint globular. Eyes and ocelli very large and prominent. Mesonotum without Mayrian furrows. Postpetiole campanulate; first gastric segment large; legs slender.
The genus Solenopsis is cosmopolitan, but represented by the greatest number of species in the Neotropical Region. There are a few forms even in Australia. The species with small, nearly blind, yellow workers, like S. fugax (Latreille) of Eurasia and S. molesta (Say) of North America, are hypogaeic and usually live in the nests of other ants and termites, feeding on their brood (cleptobiosis). Some species, however, ( punctaticeps , saevissima , geminata , gayi, etc.) live in large independent colonies. S. saevissima and geminata , the well-known "fire-ants" of the tropics, sting very severely. They have well-developed eyes and lead an epigaeic life, not only feeding on insects and other animal food but also harvesting seeds or destroying the tender shoots or fruits of plants.