Formicoxenus gebaueri is described, a guest ant within nests of Formica.
Formicoxenus is a socially parasitic genus known from temperate regions that has a peculiar lifestyle living within nests of Formica species. Unlike temporary parasites that usurp their host species, this genus relies on living within the nests of their hosts to acquire resources while staying at relatively low numbers, and usually interacts minimally with them; their small size helps accomplish this, as is common in other xenobionts. The well-known "thief ants" such as certain Solenopsis species share a similar lifestyle, but are usually less reliant on their hosts. In the case of Formicoxenus, it is theorized that individuals may prey upon host brood, or may otherwise retrieve food collected by hosts.
In this recent study by Bernhard Seifert, the new oriental member of Formicoxenus is described from nests of an undescribed claustral (non-parasitic, or independent) Formica species. However, it is mentioned that Formicoxenus are flexible in host selection due to having a functional worker caste, unlike workerless inquilines that require more attention from hosts.
Additionally, a new Leptothorax species from the same region is described, Leptothorax tibeicum, but it is not a parasite. A key is provided for the identification of both genera within the Palearctic. Nearctic species are not included, as the Formicoxenus from the region may prove to be unrelated to their Old World counterparts, more closely aligned with Leptothorax; future genetic analyses will help answer these sorts of taxonomical questions.