Socially parasitic ants use the nests and workforce of other ant species to raise their own offspring. The queens of social parasites need to get inside the nests of other ants, where they will lay eggs which are reared by the workers of their host. The next generation of social parasites is therefore raised by the host ant colony in much the same way as a cuckoo is raised by its bird host. Social parasites are typically found in temperate regions, but two tropical socially parasitic species of fungus-growing ants in the genus Pseudoatta have been known for nearly a century.

Recently a new socially parasitic species of fungus-growing ant has been discovered, which has a rather different life history (Schultz et al. 1998). The picture below shows a queen of this social parasite, Acromyrmex insinuator, being harassed by a worker of its host species, Acromyrmex echinatior.

Many social parasites have evolved to exploit their hosts very efficiently. For example, Pseudoatta social parasites have no worker caste, so that only new queens and males are produced by a queen when she parasitises an Acromyrmex nest. The queens and males of Pseudoatta are also morphologically very specialised, which may allow them to gain access to and from their host ant colonies more easily.

Acromyrmex insinuator, on the other hand, is very similar to other non-parasitic Acromyrmex species, particularly its host, Acromyrmex echinatior. It also produces workers as well as new queens and males. Social parasites are often very closely related to their hosts, and it seems likely that Acromyrmex insinuator diverged from Acromyrmex echinatior relatively recently. Acromyrmex insinuator is therefore an ideal organism to study the evolution of social parasitism.

Research is currently being carried out at the University of Copenhagen into the biology and social structure of Acromyrmex insinuator and its affect on its host Acromyrmex echinatior.