Description.

Pitts et. al. (2018) – A member of the Solenopsis saevissima species-group. As noted with the workers (Trager 1991; J. Pitts and K. R. Ross, pers. obs.), the gynes are highly variable in color. The darker variants of gynes are found in southeastern Brazil to Uruguay and Argentina and are associated with the darker workers. A lighter variant occurs in the northern area of the species’ range. The gynes and workers of these colonies are also similar in coloration. A third variant, a light orange form, is found in the Pantanal region of Brazil. This form has larger workers and gynes. No morphological differences could be found between these forms, other than size and coloration.

The darker colored gynes of S. invicta look most similar to Solenopsis megergates and Solenopsis quinquecuspis. However, the CI and OI of S. invicta gynes are normally smaller than those of S. megergates and the OI of S. invicta is normally smaller than that of S. quinquecuspis. The lighter gynes of S. invicta look similar to Solenopsis richteri and Solenopsis interrupta. The gynes of S. interrupta normally are lighter in coloration than S. invicta, have larger cephalic foveolae, and sometimes have distinct striations between the foveolae. The OOI of S. invicta gynes is normally greater than that of S. richteri, and the postpetiole of S. invicta gynes has straight sides, unlike the concave sides of S. richteri. In many cases, the sculpture of the mandible and postpetiole can help separate S. invicta gynes from similar species. The gynes of S. invicta normally have the most densely sculptured postpetiole compared to the other species.

The male of S. invicta is dark in coloration and is similar to most of the other darker species. The pubescence of the S. invicta male is longer and denser than that of Solenopsis saevissima. Sometimes the head of the S. invicta male is shagreened as in S. interrupta. The gena of the male is much more sculptured than in other species. In moderate to extreme forms, this feature is easily recognized and it may be autapomorphic for S. invicta.

Buren (1972) – Similar to Solenopsis richteri. The best and easiest method of distinguishing invicta from richteri is by the morphological characters given in the descriptions, particularly those concerning the shapes of the head, thorax, and postpetiole. Reiterated, in richteri the sides of the head are usually broadly elliptical in shape and lack the weakly cordate shape seen in invicta; the peaks of the occipital lobes nearer the midline and the occipital excision more creaselike in richteri than in invicta; scapes longer in richteri than in invicta in relation to their ability to reach toward the occipital peaks; pronotum with strong and rather angulate shoulders in richteri, this character nearly absent in invicta; a shallow but distinctly sunken area on posterior median dorsum of the pronotum of large workers in richteri, absent in large workers of invicta; the promesonotum strongly convex in profile in invicta, more weakly so in richteri; in profile the base of propodeum elongate and straight in richteri, convex and shorter in proportion to the declivity in invicta; the postpetiole wide and with straight or diverging sides posteriorly in invicta, narrower and usually with converging sides in richteri; transverse impression on posterodorsal face of postpetiole usually apparent and strong in richteri, usually weak or absent in invicta.