General description: The concept of the “Tetramorium caespitum complex” has changed many times on the basis of different approaches, from a very wide interpretation of the species Tetramorium caespitum (Linnaeus, 1758) (Radchenko, 1992a, 1992b) through differentiation of species by features of males (Seifert, 1996; Radchenko, 1998 et al.) to separation of “cryptic species” based on “integrative taxonomy” (Wagner et al., 2017). At present, I do not see any possibility of any reliable differentiation numerous specimens of “Tetramorium caespitum complex” from the Lower Volga Region (characterized by high variability of morphological features) into separate species. Characteristics of “cryptic” species given by Wagner and co-authors (2017) seem to be insufficiently reliable. Therefore, here the species T. caespitum is given in the old, very wide conception. In the Lower Volga region it is one of the most abundant species of ants in all moderately humid habitats such as grassland, grassy depressions in steppes and deserts, anthropogenic landscapes etc.

Radchenko, A. G. 1992a. Ants of the genus Tetramorium (Hymenoptera, Formicidae) of the USSR fauna. Report 1. [In Russian.]. Zoologicheskii Zhurnal 71(8):39-49.
Radchenko, A. G. 1992b. Ants of the genus Tetramorium (Hymenoptera, Formicidae) of the USSR fauna. Report 2. [In Russian.]. Zoologicheskii Zhurnal 71(8):50-58.
Seifert, B. 1996B. Ameisen beobachten, bestimmen. Augsburg: Naturbuch Verlag, 351 pp.
Radchenko, A. G.; Czechowski, W.; Czechowska, W. 1998. The genus Tetramorium Mayr (Hymenoptera, Formicidae) in Poland - a survey of species and a key for their identification. Annales Zoologici (Warsaw) 48:107-118.
Wagner, H. C.; Arthofer, W.; Seifert, B.; Muster, C.; Steiner, F. M.; Schlick-Steiner, B. C. 2017. Light at the end of the tunnel: Integrative taxonomy delimits cryptic species in the Tetramorium caespitum complex (Hymenoptera: Formicidae). Myrmecological News 25:95–129.