Formica fusca, a common black colored ant found in Europe, is a palaearctic ant with a range extending from Portugal in the west to Japan in the east and from Italy in the south to Fennoscandia in the north. F. fusca nests are usually found in rotten tree stumps or under stones in clearcut areas and along woodland borders and hedgerows.
Colonies are facultatively polygynous (though weakly so); though the queens coexist amicably, contribution to the brood tends to be unequal. Nests are usually small, containing 500–2,000 workers. The workers are large, at 8–10 millimetres (0.3–0.4 in) long, and fast moving, though timid. To ensure that non-nest mate eggs are not reared, these workers will engage in a process known as worker policing.
F. fusca feeds on small insects, aphid honeydew and extra floral nectaries. Alate (winged) forms are produced in June/July and nuptial flights are in July/August.
Workers have been found to have a very high resistance to some pathogens and its thought this may be due to F.fusca utilising the antibiotic properties of their formic acid, additional to the use of their metapleural gland.
A recent study has found evidence of nepotism in F. fusca, in contrast with previous experiments with other ant species; this conclusion has been challenged, however, on the grounds that the observed pattern may result from differences in egg viability.