Tetramorium caespitum

Bolton, B., 1979, The ant tribe Tetramoriini (Hymenoptera: Formicidae). The genus Tetramorium Mayr in the Malagasy region and in the New World., Bulletin of the British Museum (Natural History) Entomology 38, pp. 129-181 : -

The caespitum -group

Antennae with 12 segments, sting appendage triangular to dentiform. Anterior clypeal margin entire, without a median notch or impression. Frontal carinae short, sometimes virtually absent, never extending back as far as posterior margins of eyes and generally much shorter. Antennal scrobes absent. Metanotal groove almost always impressed in profile, even if only weakly so. Propodeal spines short, usually reduced to a pair of triangular teeth, sometimes reduced to tubercles. Nodes of both petiole and postpetiole in dorsal view at least as broad as long, usually distinctly broader than long. Scapes and hind tibiae dorsally without long, erect or suberect hairs but often with suberect or subdecumbent-appressed pubescence. Dorsal surfaces of alitrunk, pedicel segments and gaster with elongate fine hairs at least in part, never with all hairs short, stout and blunt. Sculpture of head of fine, regular longitudinal rugulation or reduced, in some species the head virtually unsculptured.

This is the dominant and only endemic group of Tetramorium in the Palaearctic region. One species, caespitum , has been introduced into North America (M. R. Smith, 1943; Brown, 1957) and it is now well established in the U. S. A. with a wide range on that continent (Creighton, 1950). The taxonomy of the caespitum-group is in a very poor state, with over 100 names, the majority described as infraspecific or infrasubspecific forms of caespitum itself and many of the names based on meaningless characters or represented by descriptions which can only be called valueless. Because of this a formal description of caespitum is not given here, but the species as it occurs in North America should be easily recognizable from the following summary as it is the only member of its group established on that continent.