Solenopsis nigella species complex

The following is based on: Pacheco, J.A. & Mackay, W.P. 2013. The systematics and biology of the New World thief ants of the genus Solenopsis (Hymenoptera: Formicidae). Edwin Mellen Press, Lewiston, New York. 501 pp. PDF

Solenopsis nigella Species Complex / Key to workers / Clave a las obreras

This is a group of New World thief ants in the genus Solenopsis.

Diagnosis - The workers of this complex can be distinguished by their large eyes (20-60 ommatidia), well developed clypeal carinae that extend into welldeveloped lateral teeth, the presence of horizontal striae that cover both the mesopleuron and metapleuron entirely and with S. metanotalis the pronotum as well, most species are sparsely to moderately pilose. The posterior margin of the propodeum is angled with a flattened dorsopropodeum, not rounded as in other species complexes. The petiolar node has steep sides and forms a sharp, scale-like node. Most species have a well-developed subpeduncular tooth or flange (exception of S. oculata). The members of this species complex appear to be found only in South America, especially in southern Brazil, Uruguay and northern Argentina.

The members of this species complex can be separated into two subgroups, the nigella subgroup (S. nigella and similar species) and the metanotalis subgroup (S. metanotalis and sister forms). The nigella subgroup is comprised of concolorous dark brown species that have horizontal striae on the metapleuron and mesopleuron. The members of the metanotalis subgroup are bicolored reddish-brown with dark brown gasters and have punctate/roughened sculpturing on the petiole and postpetiole in addition to the horizontally striated mesosoma.

Solenopsis andina, S. gensterblumi and S. nigella are extremely similar in form and may be members ofthe same polymorphic species, with S. andina as the larger majors, S. gensterblumi as the minor workers and S. nigella as the intermediate sized workers. Based on the available material (few specimens), the three appear to be monomorphic and will be recognized as valid species and placed in the key as such, however additional collections or future molecular analyses may allow us to better understand the relationship between these similar taxa.

Two species, S. macrops and S. photophila, are unique within the species complex in that they have very large (30-35 ommatidia), kidney-shaped eyes that nearly reach the mandible insertion and are placed within the nigella subgroup as they are concolorous dark brown, although S. photophila has punctate/roughened sculpturing on the mesopleuron, metapleuron, petiole and postpetiole.