The cosmopolitan genus Solenopsis Westwood 1840 contains 185 species of ants. Probably the best known species of Solenopsis are the fire ants. Several of the fire ants, including S. invicta Buren, the red imported fire ant, belong to the S. saevissima speciesgroup, a primarily Neotropical assemblage formerly called the S. saevissima complex of the S. geminata species-group. In this study, the S. saevissima species-group is characterized, its males, queens, and larvae are described, its workers are diagnosed, a key to the group is provided, and the distributions of the species are summarized. Solenopsis altipunctata sp. nov., discovered in the Serra Geral mountains in Santa Catarina State, Brazil, is described as new. A cladistic analysis of the S. saevissima species-group, including the social parasite S. daguerrei Santschi, yields the following results based on characters from workers, males, queens, and larvae: (daguerrei + ((electra + pusillignis) + (saevissima + (pythia + ((altipunctata sp. nov. + weyrauchi) + (interrupta + (richteri + (invicta + (megergates + (quinquecuspis + macdonaghi)))))))))). It is hypothesized that the social parasite S. daguerrei occupies a basal position in this species-group and is the sister group to all other species. It is not closely related to its hosts. As such, the results do not support Emerys Rule, which claims that social parasites evolve directly from their hosts in Hymenoptera. A review of literature shows that all the modern cladistic analyses that have tested Emerys Rule failed to support it. This seriously undermines the proposed theories that social parasites evolve from within populations of their host species by achieving reproductive isolation under sympatric conditions. As in most Hymenoptera, Solenopsis has a haplodiploidy mechanism of sex determination. This type of sex determination lends itself to certain genetic defects, such as gynandromorphy. Two gynandromorphs of S. quinquecuspis where found and are described. Because imported fire ants have become a major pest in the United States, phorid flies of this genus Pseudacteon are of great interest as potential biocontrol agents against the imported fire ants. In Arizona, S. aurea is reported as a new host species for Pseudacteon crawfordi.