Strumigenys brevisetosa

Identification
Strumigenys brevisetosa can be easily distinguished from most Nearctic species by the presence of a distinct peripheral groove that runs the entire free margin of the clypeus, placing it in the clypeata group. Of species in the clypeata group it is most similar to Strumigenys laevinasis and Strumigenys clypeata. Members of Strumigenys brevisetosa are distinguished from S. laevinasis by their linear-spatulate pilosity on dorsum and free margins of the clypeus (in S. laevinasis these hairs are fine and never expanded along their lengths). Strumigenys brevisetosa is distinguished from S. clypeata by the elevated positioning and elongated hairs on the clypeal dorsum (in S. clypeata, dorsal clypeal hairs are scale-like spatulate hairs that are tightly appressed), as well as the longer more linear hairs on the free margins of their clypeus (in S. clypeata, this fringe of hairs are spatulate, not linear spatulate).

Distribution based on Regional Taxon Lists
Nearctic Region: United States.

Nomenclature

 *  brevisetosa. Strumigenys (Cephaloxys) clypeata var. brevisetosa Smith, M.R. 1935: 215 (w.) U.S.A. (Mississippi).
 * Brown, 1953g: 60 (q.).
 * Combination in S. (Trichoscapa): Smith, M.R. 1947f: 587.
 * Combination in Smithistruma (Smithistruma): Smith, M.R. 1951a: 827; Brown, 1953g: 59.
 * Junior synonym of pilinasis: Brown, 1964a: 197; Bolton, 2000: 106.
 * Status as species: Wesson, L.G. & Wesson, R.G. 1939: 108; Wesson, L.G. & Wesson, R.G. 1939: 108 (in key); Smith, M.R. 1947f: 587; Creighton, 1950a: 304; Smith, M.R. 1951a: 828; Brown, 1953g: 59 (redescription); Wilson, 1954: 485; Smith, M.R. 1958c: 136; Booher, 2019: 405.
 * medialis. Strumigenys (Cephaloxys) medialis Wesson, L.G. & Wesson, R.G. 1939: 94, pl. 3, fig. 1 (w.q.) U.S.A. (Ohio).
 * Status as species: Creighton, 1950a: 307.
 * Junior synonym of pilinasis: Smith, M.R. 1951a: 828; Brown, 1953g: 60; Bolton, 2000: 106.
 * Junior synonym of brevisetosa: Booher, 2019: 405.

Taxonomic Notes
Booher (2019): There is a fairly long history of confusion in the species concept of Strumigenys brevisetosa. It has the most variable clypeal hair and clypeal shape of any North American Strumigenys. It is likely that S. brevisetosa is a single species that has hybridized or still hybridizes with both S. laevinasis and S. clypeata (Brown 1964). It is also possible S. brevisetosa contains more than one cryptic species: one or two that are more closely related to S. laevinasis and one that is more closely related to S. clypeata. Strumigenys medialis (junior synonym of brevisetosa) originally referred to species more similar to S. laevinasis and Strumigenys brevisetosa referred to species more similar to S. clypeata (Brown 1964). Another potential closely related species, mentioned as Strumigenys near Strumigenys pilinasis, represents morphological variants that are closest to S. laevinasis. However, after examining all of the type specimens, nearly all the collection material available to previous taxonomists, and additional new collections, it has become clear that there are no distinct morphological characters to distinguish S. brevisetosa from S. medialis and I retain it as combined for the same reasons as Brown (1964) combined these two species. Specimens that are most similar to S. laevinasis tend to have one scrobal hair (at apical position, but this varies within the same nest series), have a smooth non-sculptured patch on the side of the pronotum, conical and stout teeth, and a clypeus that is longer than wide. Specimens that are more similar to S. clypeata tend to have two scrobal hairs (one along midlength and one at apical position, though rarely a specimen will have only one at apicoscrobal position), the side of pronotum with punctate and striate sculpture and without a smooth patch, spiniform elongate teeth, and a clypeus that is wider than long. However, after looking at many more specimens than were available to my predecessors, it has become clear that none of these characters are stable and at this time I am reluctant to separate S. brevisetosa into more than one species.

Brown (1964: 199) mentioned a possible new species as Strumigenys sp. near brevisetosa, based on two worker collections (Karber’s Ridge, Perry County, IL [Sanderson & Standard]; and Urbana, Champaign County, IL [Tanquary]). I identify these as Strumigenys brevisetosa.