Trichomyrmex abyssinicus

Identification
Bolton (1987)

Worker. TL 2-6-6-7, HL 0-68-2-04, HW 0-60-1-94, CI 86-100, SL 0-50-1-06, SI 55-110, PW 0-38-0-90, AL 0-72-1-74 (40 measured).

Workers in any series showing remarkable size variation and exhibiting simple monophasic allometry. Mandibles longitudinally rugose, armed with 3 teeth; sometimes also with a minute offset basal denticle or blunt angle following the basal tooth. In larger workers the 3 teeth sometimes blunted or worn away. Anterior clypeal margin concave medially between a pair of prominent teeth which are situated on the margin in front of the antennal insertions. These teeth tend to be relatively larger, longer and more acute in small workers than in large ones. Eyes set slightly in front of the midlength of the sides, the maximum diameter of the eye 0-14-0-24 x HW; the relative size of the eye decreasing with increased head size.

Relative length of scape decreasing with increased head size, as follows.

When HW < 0-70 then SI is >90;

when HW 0-70-1-00 then SI 88-75;

when HW 1-00-1-30 then SI 75-66;

when HW 1-30-1-60 then SI 66-58;

when HW l-60->l-90 then SI 58-55.

In large workers the head in full-face view with the sides approximately straight and more or less parallel; in small workers the sides of the head diverging anteriorly. With alitrunk in profile the metanotal groove impressed. Propodeal spiracle a vertical or near-vertical ellipse of slit. Petiolar peduncle with a conspicuous anteroventral process which when best developed consists of a triangular lamella followed by a broad flange. This process varies considerably in shape and size between series, and between differently sized members of the same series. At its most reduced the process appears as an elongate flange with a rounded anteroventral angle. Petiolar spiracle at or close to the midlength of the peduncle. Elongate standing hairs sparse on cephalic dorsum in large workers, may be absent in smallest individuals. Entire dorsum of head with short decumbent to appressed pubescence, relatively sparse and directed towards the midline. Dorsal alitrunk with numerous standing hairs in largest workers but these may be absent from the propodeum in small workers. In the very smallest individuals the promesonotum may also lack standing hairs. Petiole, postpetiole and gaster with sparse backward directed hairs and with decumbent to appressed moderately dense pubescence.

Dorsum of head behind the costulate or rugulose clypeal region utterly smooth and featureless between scattered hair-pits. In all workers except the very smallest the area on the side of the head between the eye and the clypeus with longitudinal costulae or rugulae. Promesonotal dorsum longitudinally rugulose or with disorganized rugulae, to smooth. Sometimes with a few widely scattered punctulate patches or faint rugular vestiges. In general larger workers are more strongly sculptured than smaller workers. Propodeal dorsum transversely to obliquely rugulose in large to medium workers, the rugulae becoming weak and irregular with reduced size, almost obliterated in the smallest. In the range from largest to smallest workers punctate sculpture usually becomes more apparent with decreasing size on the propodeal dorsum. Sides of alitrunk sculptured, again the density and intensity diminishing with decreasing size. First gastral tergite unsculptured in all sizes.

Colour varying between series and between individuals of different sizes in the same series. Large to medium workers varying from reddish brown to dark brown with a reddish tint, sometimes with reddish black areas on the head and alitrunk. Gaster darker than head and alitrunk, usually blackish brown to black. Smallest workers much lighter in colour, with the head and alitrunk dull yellowish brown to light brown and the gaster darker in shade.

Distribution based on Regional Taxon Lists
Afrotropical Region: Benin, Burkina Faso, Ethiopia, Ghana, Nigeria, Sudan, United Arab Emirates.

Nomenclature

 *  abyssinicus. Holcomyrmex abyssinicus Forel, 1894b: 83 (w.) ETHIOPIA. Viehmeyer, 1923: 91 (q.). Combination in Monomorium: Forel, 1910f: 250; in Trichomyrmex: Ward et al., 2014: 16. See also: Bolton, 1987: 321.