Trichomyrmex oscaris

A widely distributed and versatile species which ranges over most of the Afrotropical region outside the rainforest zone or within that zone in cleared areas. Arnold (1916) records that in Zimbabwe it nests under stones along with a small species of termite, but that the galleries of the two are not interconnected. In Nigeria I have found oscaris in termitaria and nesting in the earth, but on one occasion a nest was found in an old and rotting cocoa pod which was still attached to the tree, some distance above the ground. (Bolton 1987)

Identification
Bolton (1987) - The closest relative of oscaris appears to be the pantropical tramp-species destructor, but the two are separable by the shape of the petiole node in dorsal view, especially in larger workers. In Trichomyrmex destructor the node is globular to subglobular but in oscaris it is strongly anteroposteriorly compressed and markedly transverse. Also, at any given worker size, the scapes tend to be longer in destructor than in oscaris.

Distribution based on Regional Taxon Lists
Afrotropical Region: Botswana, Burkina Faso, Democratic Republic of Congo, Eritrea, Ethiopia, Ghana, Nigeria, Senegal, South Africa, Uganda, United Republic of Tanzania, Zimbabwe.

Nomenclature

 *  oscaris. Monomorium oscaris Forel, 1894b: 86 (w.) ETHIOPIA. Combination in Trichomyrmex: Ward et al., 2014: 16. Senior synonym of despecta, dispar, kalahariense, prossae, solleri: Bolton, 1987: 326.
 * dispar. Monomorium dispar Emery, 1895h: 24 (w.) SOUTH AFRICA. Combination in M. (Parholcomyrmex): Wheeler, W.M. 1922a: 874. Junior synonym of oscaris: Bolton, 1987: 326.
 * kalahariense. Monomorium destructor subsp. kalahariense Forel, 1910f: 18 (w.) BOTSWANA. Junior synonym of oscaris: Bolton, 1987: 326.
 * solleri. Rhoptromyrmex solleri Forel, 1910e: 430 (q.) SENEGAL. Combination in Monomorium: Ettershank & Brown, 1964: 18. Junior synonym of oscaris: Bolton, 1987: 326.
 * bulawayense. Monomorium amblyops r. bulawayense Forel, 1914d: 247 (w.) ZIMBABWE. Arnold, 1916: 237 (q.m.). [Junior primary homonym of bulawayensis Forel, above.] Replacement name: prossae Forel, 1916: 418.
 * prossae. Monomorium amblyops r. prossae Forel, 1916: 418. Replacement name for bulawayense Forel, 1914d: 247. [Junior primary homonym of bulawayensis Forel, 1913j: 217.] Combination in M.(Parholcomyrmex): Wheeler, W.M. 1922a: 873. Raised to species: Emery, 1922e: 173. Junior synonym of oscaris: Bolton, 1987: 326.
 * despecta. Monomorium destructor var. despecta Menozzi, 1931a: 154 (w.) ETHIOPIA. [First available use of Monomorium destructor subsp. kalahariense var. despecta Forel, 1910c: 252; unavailable name.] Forel, 1913b: 331 (q.). Junior synonym of oscaris: Bolton, 1987: 326.

Bolton (1987) - It is possible that the names ominosa and atomaria, both described from East Africa and subsequently synonymized with destructor, may represent early records of oscaris. However, as the original descriptions are so poor, and as the specimens involved seemingly have long since disappeared, there is no way of proving this; in consequence they are left undisturbed as junior synonyms of destructor. The West African population of oscaris may eventually prove to be separable at species-level from the eastern and southern population. Females of the western population, which correspond to the name solleri in the above synonymy, are lighter in colour and tend to have the mesoscutum relatively broad. The largest workers from this area tend to show faint cephalic sculpture. The amassing of more material will be necessary before a meaningful analysis of these features can be undertaken.

Worker
Bolton (1987) - TL 1.6-3.8, HL 0.46-0.94, HW 0.36-0.84, CI 76-90, SL 0.34-0.54, SI 63-94, PW 0.24-0.52, AL 0.48-1.00 (30 measured).

Workers showing marked size variation in any given series, and displaying monophasic allometric variation. Mandibles with 3 strong teeth, the fourth (basal) tooth reduced to a minute offset denticle or even lost in the smallest workers. Mandibles frequently showing longitudinal rugular sculpture but often smooth. Usually larger workers have the mandibles more strongly sculptured than smaller individuals, but this is by no means universal. Eyes relatively small, the maximum diameter 0.13-0.19 x HW and with 3-6 ommatidia in the longest row. Eyes of larger workers have more ommatidia than those of smaller workers but are smaller in relation to the size of the head. In small workers, with HW < 0-60, the eyes are approximately 0-15-0-19 x HW, whilst in workers with HW > 0.60 the eyes range 0-13-0-16 x HW. In large workers CI is higher than in small, the heads being relatively broader. Antennal scapes relatively longer in small workers and shorter in large workers, as follows.

When HW 0-35-0-45 then SI is 94-84;

when HW 0-45-0-55 then SI is 84-79;

when HW 0-55-0-65 then SI is 76-69;

when HW 0-65-0-75 then SI is 74-64;

when HW 0-75-0-85 then SI is 65-63.

When laid straight back from their insertions the scapes almost reach the occipital margin in smallest workers but fall far short of the margin in the largest individuals. With the head in full-face view the sides shallowly convex and the occipital margin shallowly concave in large workers; in small workers the sides and occipital margin tend to become straighter. Alitrunk in profile with promesonotum convex, the metanotal groove impressed. In dorsal view the petiole node conspicuously anteroposteriorly compressed in large workers, distinctly much broader than long. Postpetiole in dorsal view broader than long. Occipital margin of head with 2-4 or more pairs of standing hairs forming a transverse row. Dorsum of head in front of this row but behind the frontal lobes with 1-4 pairs of standing hairs straddling the midline. Pubescence on head sparse, directed towards the midline. Promesonotal dorsum always with numerous standing hairs; such hairs also present on propodeum in large to medium workers but sometimes absent in small individuals. Petiole, postpetiole and gaster each with numerous elongate backward directed hairs.

Sculpture usually absent from cephalic dorsum, the surface glassy smooth between scattered hair-pits. Medium to large workers with a band of fine transverse striolate sculpture on the rim of the descending occipital surface of the head; this band of weak sculpture usually just visible in full-face view along the rim of the occipital margin. In smaller workers this transverse occipital sculpture is much reduced or absent. Largest workers in some West African samples with the cephalic dorsum showing very fine vestiges of sculpture between the hair-pits. Propodeal dorsum always finely transversely striolate to transversely rugulose; fainter in smaller workers than in larger. Promesonotal dorsum usually smooth with scattered hair-pits, but faint scratch-like or patchy striolate sculpture occurs in the large workers of some samples; a small patch of superficial punctulation may occur at the pronotal-mesonotal junction. Sides of pronotum smooth to vestigially striolate, the remainder of the lateral alitrunk punctuate to reticulate-punctate. First gastral tergite smooth except for hair-pits. Colour yellow to light brownish yellow, glossy.

Type Material
Bolton (1987) - Holotype worker, ETHIOPIA: 'Sudabessinien' (Ilg) [examined].