Tetramorium aculeatum species group
Based on Bolton 1980.
Mandibles smooth or sculptured, armed with 3 teeth apically, followed by a row of 5~7 denticles. Palp formula usually reduced from the basic tetramoriine count of 4, 3 (either 4, 2 or 3, 2; apparently 4, 3 in Tetramorium rimytyum). Anterior clypeal margin usually flattened or weakly impressed medially, less commonly entire or strongly notched. Frontal carinae weakly developed and short, ending at or in front of the level of the posterior margins of the eyes. Antennal scrobes absent. Scapes long, SI > 100. With head in full-face view the eyes prominent and the sides behind the eyes rounding broadly and evenly into the occipital margin; the latter usually convex. Metanotal groove usually impressed in profile but only feebly so in some populations. Propodeum usually armed with a pair of spines, but these may be reduced in some cases. Petiole in profile shaped as in figures; in dorsal view the node as broad as or broader than long. All dorsal surfaces of head and body clothed with numerous long fine acute hairs, the scapes and middle and hind tibiae with similar standing hairs or with standing dense pubescence.
This group contains the four recognizable species which formerly constituted the genus Macromischoides, now synonymized. The obvious artificiality of this genus was pointed out in the first part of this survey (Bolton, 1976: 363) and this argument is now strongly reinforced by the discovery of T. rimytyum, a species intermediate between Tetramorium aculeatum - Tetramorium africanum of this group and Tetramorium metactum - Tetramorium youngi of the setigerum-group, which shows quite plainly where the origins of the aculeatum-group lie.
The four species are closely related arboreal forms which are more or less restricted to forest or woodland zones in Africa, but appear to be absent from the extreme south of the continent. All the species except T. aculeatum itself are restricted to West and Central African forests. T. rimytyum and Tetramorium rotundatum are uncommon, the former being known only from the type-locality in Ghana and the latter from Gabon and Zaire but only from the queen caste. T. africanum is more widespread, being distributed throughout the wet forest belts of West and Central Africa, but nowhere does it appear to be very common. T. aculeatum on the other hand is truly a dominant and very successful species and occurs in forested or wooded areas virtually throughout Africa. It has also successfully invaded areas cultivated by man where tree or bush crops are grown, particularly cocoa and coffee plantations, and has thus achieved some economic significance (see discussion of T. aculeatum for references).