Tetramorium atratulum formerly known as Anergates atratulus is an obligate workerless parasite (inquiline) in the colonies of another ant, Tetramorium caespitum. As with many socially parasitic ants, atratulum appear to be related to its host genus and the female morphology is superficially similar. Gynes are about about 2.5mm long, blackish-brown with yellow legs.
The distribution and status of T. atratulum is, not surprisingly, closely linked to that of its host species, which is itself only locally common. T. atratulum has been recorded from the cliffs at Bolt Head and Bolberry Down in S. Devon, the heathlands of Purbeck and around Wareham and Hurn in Dorset, near Burley and Beaulieu Road Station in the New Forest and the heaths at Longmoor in Hants, Pirbright Common in Surrey and the shingle beds around Dungeness. It has also been recorded from Jersey. This parasite is possibly under-recorded. It is present in only a small proportion of host colonies, it is easily overlooked, and the Tetramorium nests are difficult to excavate. T. atratulum is found across the Palaearctic and, along with its host, it has become well established in the eastern United States.