Strumigenys concolor

Identification
Bolton (2000) – A flagellate apicoscrobal hair present, the margin indented or impressed at the site of the hair. Cephalic dorsum with 2-4 apically clavate standing hairs behind highest point of dorsum, none in front of highest point. Pronotal humerus with a flagellate hair. Mesonotum with a single pair of standing hairs, situated anteriorly. Pronotal dorsum reticulate-punctate. Postpetiole with a single pair of standing hairs. Ground-pilosity of head and alitrunk short sparse and inconspicuous, closely applied to the surface. Pleurae unsculptured at least on lower halves. Bolton (1983) - This small species was earlier treated as a synonym of Strumigenys serrula. The two are separated by the following characters in the worker.

One other species is close to concolor, the common Strumigenys lujae, a species that shows a remarkable size range but whose diagnostic characters remain quite stable. S. concolor is persistently small, overlapping only the lower end of the range of lujae, and it differs by having 2-4 standing hairs posteriorly on the cephalic dorsum which are distinctly clavate apically, as opposed to the 6 fine hairs on the cephalic dorsum in lujae which are scarcely or not at all swollen apically. In lujae the 6 hairs are arranged in a posterior row of 4 and an anterior pair, situated just in front of the highest point of the vertex. The postpetiole in concolor always bears a single pair of stout hairs; in lujae two or more pairs occur.

I consider it possible that concolor, as presently constituted, may consist of two sibling species. It is noticeable that the samples with a single pair of standing cephalic hairs have the upper scrobe margins more strongly impressed at the site of the projecting hair than do those with two pairs of standing hairs.

Distribution based on Regional Taxon Lists
Afrotropical Region: Angola, Cameroun, Chad, Democratic Republic of Congo, Equatorial Guinea, Gabon, Ghana, Ivory Coast, Kenya, Uganda.

Nomenclature

 *  concolor. Strumigenys (Trichoscapa) concolor Santschi, 1914d: 375 (w.q.) GHANA. Combination in S. (Cephaloxys): Wheeler, W.M. 1922a: 919; Emery, 1924d: 324; in Serrastruma: Brown, 1952e: 81; in Pyramica: Bolton, 1999: 1673. Junior synonym of serrula: Brown, 1952e: 81. Revived from synonymy: Bolton, 1983: 338; in Strumigenys: Baroni Urbani & De Andrade, 2007: 117. See also: Bolton, 2000: 312.

Worker
Bolton (1983) - TL 2.0-2.2, HL 0.48-0.52. HW 0.40-0.46, CI 80-90, ML 0.16-0.18, MI 32-36, SL 0.30-0.33, SI 67-80, PW 0.28-0.32, AL 0.56-0.62 (12 measured).

Mandibular denticles evenly sized to the base, without a basal series of 4-8 denticles which are enlarged though the basalmost may be larger than those preceding. Upper scrobe margins well developed, with a flagellate hair at each side just behind the level of the eye and with the margin indented or impressed at the site of the hair. Width and depth of this indentation variable, usually conspicuous in full-face view but sometimes only shallow. Ground-pilosity of head short and narrowly spatulate, closely applied to the surface and indistinct. Dorsum of head behind highest point of vertex with 2 or 4 elongate standing hairs which are anteriorly curved, stout and narrowly clavate apically. Samples with only one pair of these hairs generally have the upper scrobe margins more strongly impressed at the site of the flagellate hair than do those samples with two pairs of hairs. Entire dorsum of head densely finely reticulate-punctate. Alitrunk in profile with promesonotum convex, sloping down posteriorly to the impressed metanotal groove. Propodeal dorsum convex, sloping behind to a pair ofteeth which are variable in size. Infradental lamellae present on propodeal declivity. Sides of pronotum superficially punctulate to smooth, the pleurae usually smooth but in some their upper halves finely punctulate. Dorsal alitrunk finely reticulate-punctate everywhere but the intensity of sculpture on the pronotum variable and sometimes the punctures filled by a waxy superficial layer. Occasionally weak superficial rugulae, generally formed by alignment of puncture margins, may occur, but these are always distinctly secondary to the punctate sculpture. Pronotum with flagellate hairs present at the humeri. Mesonotum with a single anteriorly situated pair of standing hairs which are stout long conspicuous and clavate apically. Dorsal alitrunk otherwise only with sparse ground-pilosity which is short, inconspicuous and generally closely applied to the surface. Spongiform appendages of pedicel segments moderately developed in profile. Petiole in dorsal view usually punctate but the sculpture very faint in some specimens. Postpetiole usually superficially punctulate but almost smooth in some, with a posterior spongiform strip which abuts a similar narrow strip on the base of the first gastral tergite. Basigastral costulae present, the tergite otherwise unsculptured. Petiole and postpetiole dorsally each with a single pair of elongate stout hairs which are clavate apically, the first gastral tergite with numerous similar hairs. Colour yellow to yellowish brown.

Type Material
Bolton (1983) - Syntype workers, female, GHANA: Aburi [examined]. [Previously synonymized with serrula by Brown, 1952a: 81.]