There have been numerous taxonomic revisions (from different authors, done at different times, with varying care and attention to detail) that have included groupings of Solenopsis species. For organizational purposes these are here collectively referenced as Solenopsis species groups. Some of these are listed below.
The simplest grouping is the distinction between what are commonly called the fire ants, those species with large workers, worker polymorphism and large colony size versus those with small workers, the so called thief ants. The species of the latter can have small or large colonies and may or may not exhibit within species worker polymorphism.
The most recent sorting of the fire ants into groups is as follows:
Pitts et. al. (2018) - Trager (1991) placed the worker-polymorphic fire ants along with three monomorphic Solenopsis species (Solenopsis substituta, Solenopsis tridens, and Solenopsis virulens) in the Solenopsis geminata species-group, although he admitted the inclusion of S. virulens was somewhat arbitrary. Trager referred to smaller groupings within the S. geminata species-group as species complexes, and subsets of complexes as subcomplexes. The S. geminata species-group is informal and its monophyly has yet to be demonstrated. This situation, coupled with the unwieldy terminology of complexes and subcomplexes, has led us to propose a new classification of fire ants.
There is some molecular support for the monophyly of these groups (Krieger and Ross 2005, Shoemaker et al. 2006), although taxon sampling is incomplete and branch support is often weak. As such, the proposed species complexes should be viewed as preliminary until the evolutionary relationships of the fire ants have been robustly estimated using diverse character sets.
Solenopsis geminata species-group
- Solenopsis geminata
- Solenopsis xyloni
- Solenopsis amblychila
- Solenopsis aurea
- Solenopsis gayi
- Solenopsis bruesi
Strongly polymorphic workers with a short scape, long first flagellomere (at least 1.5X longer than broad), reduced or absent median clypeal tooth, and a ventral petiolar process. This species-group is equivalent to the S. geminata complex of Trager. No apomorphies are apparent for the species-group, and it may be defined entirely by simple-siomorphies.
Solenopsis saevissima species-group
- Solenopsis daguerrei
- Solenopsis electra
- Solenopsis hostilis
- Solenopsis interrupta
- Solenopsis invicta
- Solenopsis macdonaghi
- Solenopsis megergates
- Solenopsis metallica
- Solenopsis pusillignis
- Solenopsis pythia
- Solenopsis quinquecuspis
- Solenopsis richteri
- Solenopsis saevissima
- Solenopsis weyrauchi
Diagnosis of species Solenopsis saevissima species group
Strongly polymorphic workers with a long scape, long first flagellomere (at least 1.5X longer than broad), strongly developed median clypeal tooth, weak sculpturing, and a small or absent ventral petiolar process. This species-group is equivalent to the S. saevissima complex of Trager.
Solenopsis tridens species-group
Monomorphic workers with a long scape, long first flagellomere (at least 1.5X longer than broad), propodeal carinae, and an elongate petiolar peduncle. This species-group is equivalent to the S. tridens complex of Trager.
Solenopsis virulens species-group
Workers monomorphic, eye small with 20–60 facets, first flagellomere as broad as or broader than long, and postpetiole not dilated. This species-group is presumably closely related to the Solenopsis nigella species-group sensu Moreno-Gonzalez (2001), which is equivalent to Euopthalma of Creighton minus Solenopsis globularia.
The New World species of these small bodied Solenopsis species were revised by Pacheco and Mackay (2013). Details about this group as a whole, and the Pacheco and Mackay species groups, are found at the Thief ants page. species groupings: