Species Action Plan

The dark guest ant is an obligate social parasite (inquiline) in the colonies of another ant, Tetramorium caespitum. As such, its status is closely linked to that of its host species, which is itself locally distributed in Great Britain. Due to its parasitic nature, the dark guest ant is necessarily rarer than its host and it appears to survive only where population densities of T. caespitum are high. The biology of this parasite is poorly understood but newly mated queens appear either to secure adoption in a queenless colony of T. caespitum or else to lead to the host queen being killed or starved by her own workers. The dark guest ant does not have workers of its own and so the total resources of the host colony are then diverted to the development of large numbers of new dark guest ant queens and wingless males.

As no further host workers are produced, the dark guest ant queen must produce new generations before the colony dies out in about two to five years, and therefore she soon becomes massively swollen with eggs. Such queens are themselves rarely found in nests; more commonly the yellowish larvae (contrasting with the white Tetramorium larvae), the winged queens or the pale pupoidal males are found. Mating occurs within the nest and the queens then fly out from May to August to find new host colonies. Many records are due to catches of these winged queens rather than from locating parasitised nests.

In Great Britain the host ant, T. caespitum, nests in areas of dry lowland sandy heath, coastal zones and some rocky inland areas with short dry acid turf. Although T. caespitum has been recorded from coastal sites as far north as Scotland, it is predominantly a southern species requiring habitats with sparse vegetation cover (greater than 40% bare ground) and attracting high levels of insolation at the ground surface. The greatest population densities of this host species occur mainly along the south coast of Britain and on the lowland heaths of Dorset, Hampshire and Surrey. The dark guest ant has consequently been recorded from the cliffs at Bolt Head and Bolberry Down in south Devon, the shingle beds at Dungeness, 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 Hampshire and Pirbright Common in Surrey. It has also been recorded from Jersey. However, it is easily overlooked and is probably under-recorded. The dark guest ant is found across the Palearctic and, along with its host, it has become well established in the eastern United States.

In Great Britain this species is now classified as Insufficiently Known. It is classified by the IUCN (1996) as Globally Vulnerable.

Due to the sparsity of records and insufficient knowledge of the species, it is not possible to state whether the dark guest ant is actually in decline. However, since the status of the species is so closely linked to that of its host, and populations of T. caespitum do appear to be in decline (particularly on some lowland heaths), the main factors adversely affecting its host species will be relevant. These include the following:

Loss of suitable heathland habitat through urban or industrial development, agricultural improvement and afforestation.

Inappropriate heathland management.

Inappropriate coastal development or cliff stabilisation.

Changes in grazing practice where the host species occurs on short dry acid grassland and cliff-top turf.

Many of the sites where the dark guest ant has been recorded are afforded some protection as SSSIs, NNRs, or other nature reserves.

No local implementation.

Originally published in: UK Biodiversity Group Tranche 2 Action Plans - Volume VI: Terrestrial and freshwater species and habitats (October 1999, Tranche 2, Vol VI, p77)