Trichomyrmex robustior

Heterick (2006) - Trichomyrmex robustior has a wider known distribution than Trichomyrmex destructor in Madagascar. Specimens have been collected by a variety of means in dry tropical and spiny forest. In Africa, this species has been recorded from Kenya and Somalia (Bolton 1987).

Identification
Worker. TL 2.5-3.4, HL 0.68-0.84, HW 0.62-0.78, CI 90-97, SL 0.52-0.66, SI 82-88, PW 0.36-0.46, AL 0.70-0.92 (20 measured).

Mandibles strongly longitudinally rugulose, the basal (fourth) tooth reduced to a minute denticle. Maximum diameter of eye 0.18-0.20 x HW and with 6-8 ommatidia in the longest row. Sides of head feebly convex in full-face view, the occipital margin concave or indented medially. Promesonotum domed in profile, the metanotal groove shallowly impressed; propodeal dorsum on a lower level than that of the promesonotum.

Cephalic dorsum usually without standing hairs behind the level of the frontal lobes, but in some larger workers a single pair is present straddling the midline close to the occipital margin. Even more rarely a second pair may occur mid-dorsally between the level of the posterior margins of the eyes and the occipital margin. Entire dorsum of head with long fine pubescence which is decumbent to appressed and is directed toward the midline. Dorsal alitrunk also with similar appressed pubescence but all surfaces also with long standing hairs present. Petiole, postpetiole, first gastral tergite and first sternite with numerous long back-curved hairs and with sparse appressed pubescence.

Dorsum and sides of head and promesonotum unsculptured, smooth except for small scattered hair-pits. Remainder of sides of alitrunk reticulatepunctate, the metapleuron and propodeal sides usually overlaid by rugular sculpture. Propodeal dorsum finely transversely rugulose, usually with punctate interspaces, the latter variable in intensity. Petiole and postpetiole either with sculptural vestiges laterally or entirely smooth; first gastral tergite unsculptured except for scattered hair-pits. Colour medium to dark brown on the head and alitrunk, sometimes with a reddish tint. Gaster dark brown to blackish brown, usually darker in shade than the head and alitrunk.

Sharaf et al. (2016) - The most similar species to T. robustior is Trichomyrmex mayri from which it can be separated by the smooth posterior margin of the head, the strongly convex promesonotal outline, the coarse and broadly spaced propodeal sculpture, and the longer and strongly curved body pilosity.

Distribution based on Regional Taxon Lists
Afrotropical Region: Eritrea, Kenya, Saudi Arabia, Somalia. Malagasy Region: Madagascar. Palaearctic Region: Oman.

Nomenclature

 *  robustior. Monomorium gracillimum r. robustior Forel, 1892e: 352 (w.) SOMALIA. Combination in M. (Parholcomyrmex): Wheeler, W.M. 1922a: 875; in Trichomyrmex: Ward et al., 2014: 16. Raised to species: Bolton, 1987: 328. See also: Heterick, 2006: 99. [Name misspelled as robustius by Emery, 1893f: 256; Forel, 1894e: 228.]

Worker
Heterick (2006) - Lectotype: HML 1.83 HL 0.68 HW 0.68 CeI 100 SL 0.56 SI 82 PW 0.38. (non-types): HML 1.65–1.97 HL 0.62–0.76 HW 0.64–0.75 CeI 95–103 SL 0.51–0.61 SI 75–85 PW 0.36–0.46 (n=20).

HEAD: Head square; vertex planar or weakly concave; frons longitudinally finely striolate anteriad (striolae curving inwards around antennal insertions), smooth and shining posteriad; pilosity of frons consisting of abundant, incurved, appressed setulae only. Eye moderate, eye width 1–1.5× greatest width of antennal scape; (in full-face view) eyes set above midpoint of head capsule to set below midpoint of head capsule; (viewed in profile) eyes set posteriad of midline of head capsule; eye elongate with or without eye narrowed to point anteriad. Antennal segments 12; antennal club three-segmented. Clypeal carinae indistinct; anteromedian clypeal margin straight; paraclypeal setae moderately long and fine, curved; posteromedian clypeal margin approximately level with antennal fossae. Anterior tentorial pits situated nearer antennal fossae than mandibular insertions. Frontal lobes sinuate, divergent posteriad. Psammophore present. Palp formula 2,2. Mandibular teeth three, plus minute, basal denticle or angle; mandibles with sub-parallel inner and outer margins, striate; masticatory margin of mandibles strongly oblique; basal tooth a small to minute denticle or angle, much smaller than t3 (four teeth present).

MESOSOMA: Promesonotum shining and smooth on dorsum, lower mesopleuron strongly punctate; (viewed in profile) promesonotum broadly convex; promesonotal setae seven to twelve; standing promesonotal setae a mixture of well-spaced, distinctly longer, erect and semi-erect setae which are curved distally and often paired, interspersed with much shorter, incurved, decumbent setae; appressed promesonotal setulae well-spaced over entire promesonotum. Metanotal groove strongly impressed, with distinct transverse costulae. Propodeum with sculpture reduced dorsally, metapleuron punctate; propodeal dorsum slightly elevated anteriad and sloping away posteriad, propodeal angles not raised; propodeum angulate, propodeal angle blunt; length ratio of propodeal dorsum to its declivity about 1:1; standing propodeal setae consisting of two or more pairs of longer, suberect setae near propodeal angles, with shorter setae anteriad; appressed propodeal setulae very sparse or absent; propodeal spiracle equidistant from metanotal groove and declivitous face of propodeum. Vestibule of propodeal spiracle distinct. Propodeal lobes present as vestigial flanges or small strips of cuticle only.

PETIOLE AND POSTPETIOLE: Petiolar spiracle lateral and situated slightly anteriad of petiolar node; node (viewed in profile) conical, vertex rounded; appearance of node shining and smooth with vestigial microreticulation anteriad; ratio of greatest node breadth (viewed from front) to greatest node width (viewed in profile) about 1:1; anteroventral petiolar process absent or vestigial; ventral petiolar lobe absent; height ratio of petiole to postpetiole about 4:3; height–length ratio of postpetiole about 1:1; sternite not depressed at midpoint, its anterior end an inconspicuous lip or small carina.

GASTER: Pilosity of first gastral tergite consisting of well-spaced, short, thick, erect setae interspersed with minute, appressed setulae.

GENERAL CHARACTERS: Color brown, gaster chocolate. Worker caste monomorphic.

Sharaf et al. (2016) - TL 2.5–3.4; HL 0.68–0.84; HW 0.62–0.78; SL 0.52–0.66; PW 0.36–0.46; ML 0.70–0.92; CI 90–97; SI 82–88 (Bolton 1987).

Head. With feebly convex sides and slightly concave or emarginated posterior margin in full-face view; in some individuals head broader anteriorly than posteriorly; anterior clypeal margin nearly straight or shallowly concave; basal mandibular tooth reduced to minute denticle; eyes of moderate size (EL 0.18–0.20 × HW), situated just in front of midline of head and with 6–8 ommatidia in longest row; scapes when laid back from their insertions just reach posterior margin of head.

Mesosoma. Promesonotum domed in profile; metanotal groove impressed; propodeal dorsum on a lower level than that of promesonotum in profile.

Petiole. Peduncle elongate, petiolar node strongly rounded in profile.

Postpetiole. Node at a much lower level than that of petiole in profile.

Pilosity. Underside of head with few short straight hairs, not forming a psammophore; cephalic surface with long fine decumbent to appressed pubescence directed toward midline of head; mesosomal dorsum with long erect to suberect hairs and abundant appressed pubescence; petiole, postpetiole, first gastral tergite and sternite with numerous long curved backward directed hairs and with sparse appressed pubescence.

Sculpture. Mandibles longitudinally rugulose, cephalic dorsum and sides of promesonotum smooth and shining; metapleuron and propodeal sides regularly punctulate-reticulate; propodeal dorsum finely transversely rugulose; petiole, postpetiole and gastral tergites entirely smooth and shining.

Colour. Dark brown or blackish brown; gaster usually darker than head and mesosoma.

Type Material
Heterick (2006) - Lectotype: worker, Somalia, C. Keller. A lectotype has been chosen to fix the name for the species, which was originally described as simply a race of Monomorium gracillimum, itself now a synonym for Trichomyrmex destructor. The specimen, originally on a pin holding three pointed specimens, has been transferred to a single pin, along with the original labels and a lectotype label. Paralectotypes: Two pins with 12 and 13 workers, respectively, data the same as for the lectotype (MHNG). Photocopies of the original labels have been affixed to the pin with the two specimens.