Tetramorium ataxium

Identification
Tetramorium ataxium appears to be the commonest and most widely distributed member of the flabellum-complex of this group in West Africa. Its close relatives within the group include Tetramorium flabellum, Tetramorium geminatum, Tetramorium kestrum and Tetramorium sigillum, all of which are characterized by their long scapes (SI > 90, often 100 or more), coarse sculpture, rectangular petiole outline and coarse, blunted pilosity. Of these T. flabellum is immediately separable by its possession of bizarre fan-like hairs, absent from the other species, Tetramorium sigillum differs from T. ataxium by being smaller and by having an unsculptured postpetiolar dorsum, or at least a broad smooth median strip. Tetramorium kestrum occurs in eastern and southern Africa, its range does not appear to overlap that of T. ataxium, and it is much lighter in colour (yellow-brown to light orange-brown) with SI consistently 100 or more. The species closest related to T. ataxium is T. geminatum, known only from Gabon and separated on the relative lengths of pilosity in the two species as indicated in the key. Apart from this character the mandibular striation is feeble in T. geminatum and the punctulate ground-sculpture of the alitrunk and pedicel undeveloped or very feeble.

Distribution based on Regional Taxon Lists
Afrotropical Region: Central African Republic, Guinea, Ivory Coast, Nigeria.

Nomenclature

 *  ataxium. Tetramorium ataxium Bolton, 1980: 295, figs. 78, 86 (w.) NIGERIA.

Worker
Holotype: TL 3.1, HL 0.74, HW 0.64, CI 86, SL 0.64, SI 100, PW 0.46, AL 0.86. Paratypes (20 measured): TL 3.0—3.5, HL 0.74-0.80, HW 0.64-0.70, CI 84-89, SL 0.60-0.68, SI 95-101, PW 0.42-0.50, AL 0.80-0.96.

Mandibles longitudinally striate. Anterior clypeal margin entire, without a notch or impression. Median clypeal carina strongly developed, running the length of the clypeus. A few feeble rugulae branch off the median carina and run to the lateral margins of the clypeus posterior to their point of origin. Lateral portions of clypeus forming a strongly developed wall in front of the antennal insertions, seen as a high prominence when the head is viewed from above and slightly behind. Frontal carinae conspicuous, reaching back well beyond the level of the eyes and tending to merge into the rugoreticular sculpture occipitally. Antennal scapes long, SI 100 in holotype (measured range of SI 95-101 in material examined). Antennal scrobes present but shallow. Eyes moderate in size, maximum diameter 0.14, about 0.22 x HW. Propodeal spines in profile long and stout, very feebly downcurved along their length, distinctly longer than the broad, acutely triangular metapleural lobes. Petiole in profile an elongate node, the dorsal length greater than the height of the tergal portion of the node. In dorsal view the petiole node longer than broad, broader behind than in front. Dorsum of head longitudinally rugose to level of posterior margins of eyes, with few crossmeshes, but behind this zone a rugoreticulum is present. Ground-sculpture between the rugulae a fine punctulation. Dorsal surfaces of alitrunk, petiole and postpetiole reticulate-rugose with punctulate interspaces, the latter most distinct on the pedicel segments. The dorsal rugae of the petiole and postpetiole are less conspicuous or effaced on the sides of the segments and in consequence the punctulate sculpture is more distinctive there. Gaster unsculptured, smooth and shining. All dorsal surfaces of head and body with numerous coarse, often blunted hairs. The hairs on the dorsum of the head (discounting the very long ones on clypeus and occiput), and those on the first gastral tergite at most about as long as maximum diameter of eye, never obviously longer, generally rather shorter than eye diameter. Dorsal (outer) surfaces of middle and hind tibiae only with fine decumbent to appressed pubescence. Colour dark brown.

Paratypes: As holotype but colour varying from dark brown to blackish brown, sometimes with a reddish tint. Propodeal spines sometimes approximately straight but usually slightly downcurved, slightly upcurved or even feebly sinuate. Maximum diameter of eye 0.14-0.16, about 0.21-0.24 x HW.

Type Material
Holotype worker. Nigeria: Ibadan, I.1.T.A., 16—23.ix.1974 (B. R. Critchley). Paratypes, Nigeria: 5 workers with same data as holotype. Ivory Coast: 36 workers, Palmeraie de Lame, no. 8, 23.1.1976 (T. Diomande). (BMNH; ; )

References based on Global Ant Biodiversity Informatics

 * Belshaw R., and B. Bolton. 1994. A survey of the leaf litter ant fauna in Ghana, West Africa (Hymenoptera: Formicidae). Journal of Hymenoptera Research 3: 5-16.
 * Belshaw R., and B. Bolton. 1994. A survey of the leaf litter ant fauna in Ghana, West Africa (Hymenoptera: Formicidae). Journal of Hymenoptera Research. 3: 5-16.
 * Bolton B. 1980. The ant tribe Tetramoriini (Hymenoptera: Formicidae). The genus Tetramorium Mayr in the Ethiopian zoogeographical region. Bulletin of the British Museum (Natural History). Entomology 40: 193-384.
 * IZIKO South Africa Museum Collection
 * Yeo K., and A. Hormenyo. 2007. A Rapid Survey of Ants in Ajenjua Bepo and Mamang River Forest Reserves, Eastern Region of Ghana. Pp 27-29. In McCullough, J., P. Hoke, P. Naskrecki, and Y. Osei-Owusu (eds.). 2008. A Rapid Biological Assessment of the Ajenjua Bepo and Mamang River Forest Reserves, Ghana. RAP Bulletin of Biological Assessment 50. Conservation International, Arlington, VA, USA.