Based on Seifert 2002.
The members of the Formica cinerea group form a morphologically and biologically well-defined clade of exclusively West Palaearctic distribution. They are completely unknown from Turkestan, the Pamirs, Tian Shan, and other Central Asian mountain ranges or steppes where the ecological niche of the F. cinerea group is occupied by members of the Formica subpilosa group. The most widely distributed species, Formica cinerea, reaches its easternmost point in W Siberia at 85.10 E, 52.32 N (Dlussky 1967). Five species including Formica corsica and Formica georgica are recognised. Europe is most probably the radiation centre of the group - the Alps and their marginal regions are inhabited by three species.
All members of the group except F. corsica show a high tendency to build up large polycalic colonies that defend territories against other species - a trait that is rare in W Palaearctic Serviformica species. Similar to wood ants, the F. cinerea group species show cooperation during transport of larger prey items. Primary habitats of perhaps all species are xerothermous, sandy or gravelly areas along river valleys with a sparse field layer. The species are well adapted to unstable habitats with frequent shifting of soil material and early stages of plant succession. This strong pioneer performance is enabled by a combination of high dispersal capacity either by flight or as colony fragments, of well-developed potency for independent, single-queen colony foundation, and of rapid shifting to polygyny and polycaly for quickly building up dominant populations on unstable habitat spots. Following river valleys during postglacial immigration, they climbed up to 1800-2500 m in the Pyrenees, the Alps, the mountains of the Balkan, and the Caucasus, but left also primary riversides to invade sandy steppe regions, aeolic sand dunes, xerothermous forests on sandy soil, and, finally, several types of anthropogenic habitats. The species of the group need a certain percentage of bare soil surfaces to be superior competitors against other Serviformica species. A coverage of herbaceous layer plants of < 40 % is optimal and most of the F. cinerea group species will no longer occur if it approaches 90-95%.
Notes that preface the species key (follow the link above) include details about important characters that distinguish the cinerea group from others.
Within the Palaearctic members of the subgenus Serviformica, the F. cinerea group can be distinguished from any other species complex by a combination of large eyes and most developed occipital and gular pilosity. The extreme values of nest sample means range 0.30 l - 0.327 in EYE (1400), 6.0- 81.3 in nOcc, and 1.3-46.3 in nGu.
By morphology, the next related species complex is apparently the F. subpilosa group, being also similar in colony structure and habitat selection and taking over in Central Asia just the ecological niche occupied by the F. cinerea group in the W Palaearctic. The taxonomic separation of both groups might be questioned in view of the fact that Formica pamirica, the most hairy species of the F. subpilosa group and a typical river bank species, shows partial overlap with the least hairy species of the F. cinerea group in occipital and gular setae numbers. However, a clear separation of both groups and a monophyly of at least the cinerea group is supported by eye size differences which are significant for p < 0.0001 in any of the 24 possible between-group comparisons.