High Quality Content by WIKIPEDIA articles! Formica rufa, also known as the southern wood ant or horse ant, is a boreal member of the Formica rufa group of ants, commonly found throughout much of Europe in both coniferous and broad-leaf broken woodland and parkland. Workers can measure 8–10 mm in length. They have large mandibles and like many other ant species they are able to dispense 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.