The southern wood ant, Formica rufa, is the largest ant found in the UK, with workers reaching up to 10mm in length, and queens 12mm. It is a common forest species which builds large, dome-shaped nests consisting of twigs, grass and conifer needles. These nests may hold colonies of several hundred thousand workers and many queens.
As well as feeding on honeydew from aphids, the adult prey on other insects, foraging widely in search of food along marked trails extending as far as 100m from the nest. Encounters with other insects are met with aggression, using both their large mandibles and formic acid sprayed from their abdomens in defence. This species which was first used by an English naturalist, John Ray, to extract formic acid in the mid-17th century by the distillation of large numbers of crushed ants.