Formica rufa, also known as the red wood ant, southern wood ant or horse ant, is a boreal member of the Formica rufa group of ants, and is the type species for that group. It is native to Europe and Anatolia but is also found in North America, in both coniferous and broad-leaf broken woodland and parkland. Workers are bicolored red and brownish-black, with a dorsal dark patch on the head and promensonotum, and are polymorphic, measuring 4.5–9 mm in length. They have large mandibles and like many other ant species they are able to spray formic acid from their abdomens as a defence. Formic acid was first extracted in 1671 by the English naturalist John Ray by distilling a large number of crushed ants of this species.