This small, shining, reddish-yellow to brown ant is the only known European representative of its genus. It resembles Leptothorax and Temnothorax species, to which it is closely related. Females, and the wingless males, are worker-like in appearance, whilst individuals morphologically intermediate between females and workers also occur. Formicoxenus nitidulus is a ‘guest ant’, living only within the nest mounds of its ant hosts. These are usually ‘wood ants’ (Formica subgenus Formica sens. str.). Known hosts in Britain are F. aquilonia, F. lugubris and F. rufa. Although it obtains food from its hosts, F. nitidulus establishes discrete nests and rears its own brood. Whether or not it should be considered a true social parasite is therefore a matter of some debate. (See Dumpert (1981) and Hölldobler & Wilson (1990) for differing views, and (together with Donisthorpe (1927), Collingwood (1979), and studies cited therein) for more extensive accounts and discussion of information included in this profile.)
The scattered British records of F. nitidulus cover much of the areas of England, Wales and Scotland from which its hosts are recorded, but as yet it is unknown from Ireland and the Channel Islands. Elsewhere, F. nitidulus ranges from latitude 70°N to north Italy and from Spain to eastern Siberia.