Strumigenys chorosa

The type material was found in the litter of a lowland rainforest.

Identification
Bolton (2000) - A member of the koningsbergeri complex in the Strumigenys koningsbergeri-group. This species is very closely related to Strumigenys vertigosa, which comes from the same locality in Sarawak. In fact the only strong character separating the two is presence/absence of a pair of erect hairs anterodorsally on the pronotum. The independence of these two names will need reassessment when more material becomes available but until then, because the pilosity character is consistent elsewhere, the two will be retained as separate species.

Six species of the koningsbergeri-complex have a pair of short standing hairs near the anterodorsal margin of the pronotum; these hairs are shorter than the humeral pair and located anterior to them. Of these chorosa is the only species to have the entire metapleuron and side of propodeum evenly densely reticulate-punctate, without trace of smooth patches; even the katepisternum has its posterior one-third reticulate-punctate. Strumigenys nergala has broad convex lamellae on the propodeal declivity. The lamella subtends the tooth for most of its length and at its broadest is equal to the length of the tooth. It is a small species (HL 0.68-0.70, HW 0.58-0.60) with a relatively short scape (SI 57), and has spatulate or apically flattened and expanded hairs on the first gastral tergite. These cephalic dimensions are matched only by small workers of amnesia (HL 0.64-0.76, HW 0.56-0.65) but here the scape i s longer (SI 63-70) and the hairs on the first gastral tergite are simple.

The other four species form two species-pairs, based on the structure of the gastral pilosity. In amnesia and ataxia the hairs on the first tergite are simple, cylindrical and shallowly curved. Most or all of them taper to a point apically, though a few may appear narrowly blunted. In the other two species, Strumigenys hyletha and Strumigenys taraxis, most or all of the hairs on the first tergite are flattened and tend to increase in width toward their apices; they tend to be truncated, expanded, or even weakly splayed out apically. The components of each of these species-pairs separate only by the characters given in the key.

Distribution based on Regional Taxon Lists
Indo-Australian Region: Borneo, Indonesia, Malaysia.

Nomenclature

 *  chorosa. Strumigenys chorosa Bolton, 2000: 841 (w.) BORNEO.

Worker
Holotype. TL 2.8, HL 0.77, HW 0.66, CI 86, ML 0.35, MI 45, SL 0.42, SI 64, PW 0.33, AL 0.75. With characters of koningsbergeri-complex. Preocular concavity forms a shallow depression on ventral surface of head. Upper scrobe margins slightly constricted above eye, most of arc of eye visible in full-face view but not its inner margin. Depression across posterior vertex of head shallow, weakly developed. Pronotum with a pair of short standing hairs close to anterodorsal margin. Pronotal humeral hair stiff, straight and simple. A single erect pair of hairs on mesonotum. Median strip of katepisternum smooth but its anterior and posterior portions reticulate-punctate. Metapleuron and side of propodeum uniformly densely and sharply reticulate-punctate, without smooth patches or areas where sculpture is effaced. Bullae of femoral glands absent on middle and hind legs. Lamella on propodeal declivity moderately broad, its posterior (free) margin concave. Standing hairs on first gastral tergite simple and cylindrical, most of them bluntly pointed apically but one or two weakly frayed at the apex.

Type Material
Holotype worker, Malaysia: Sarawak, 4th Div., G. Mulu Nat. Pk, RGS Expd., Long Pala, 6.x.1977, leaf litter, lowland rainforest (B. Bolton).

References based on Global Ant Biodiversity Informatics

 * Pfeiffer M.; Mezger, D.; Hosoishi, S.; Bakhtiar, E. Y.; Kohout, R. J. 2011. The Formicidae of Borneo (Insecta: Hymenoptera): a preliminary species list. Asian Myrmecology 4:9-58