Solenopsis saevissima

S. saevissima belongs to the Solenopsis saevissima species group which includes 13 fire ant species that exhibit remarkably similar morphology, rendering morphological distinction nearly impossible without the aid of chemical characters. S. saevissima has polymorphic adult workers that differ in size depending on their castes: minor workers are generally smaller and major workers are relatively larger. The major workers also typically have trapezoidal heads and antennal scapes almost reaching their vertex; the minor workers have ovate heads and antennal scapes that extend past their heads. Like all species of the S. saevissima species group, S. saevissima has workers averaging 1.9 mm in length, antennae containing 10 segments, and mandibles with 4 or 5 teeth. Similarly to other species within Solenopsis, it has a conspicuous central hair on the front of its clypeus that extends beyond the outer margin of mandibles. Differently from most other species in the group, it lacks a well-developed medial clypeal tooth and its propodeum is rounded. Proper morphological identification of the species is complicated by interspecies breeding and the existence of a number of cryptic species in its native range. Currently it is believed that nominal S. saevissima actually comprises at least 5 cryptic species (i.e. of identical morphology) that can be separated using chemical characters.

S. saevissima is native to the tropical and warm climate regions of South America, especially eastern Brazil (Pelotas). It is commonly found in the disturbed areas of grasslands and forest openings due to its workers' nature as excellent recolonizers. These disturbed sites can be manmade (farms or plantation) or natural (animal trails and riverbanks). S. saevissima prefers to build its colonies in sandy soil rather than clays. Mounds can reach up to 10 feet in length and have over one million residents.

The scientific name for Solenopsis saevissima comes from the Greek: solen, which means pipe or channel, opsis, which means appearance or sight and the Latin saevissima, which means "the very cruel". Its name derive of early accounts of its viciousness as reported from the Amazon forest. S. saevissima is named so because it is known to be even more vicious than S. invicta the red imported fire ants, which costs the United States millions of dollars per year in agricultural, medical, and traffic-related damage.