Formica fusca is a dark-bodied species, 4-7 mm long, common and widely distributed on uncultivated land. This species is very similar to Formica lemani. Taxonomic and behavioural differences are given in the F. lemani profile.
Editor's note. The original profile combined the two species F. fusca and F. lemani but this has been split by the editor to follow the Atlas style.
Formica fusca is common throughout the South Midlands and lowland Britain but has a much more localised distribution in northern England, Ireland and Scotland. There is a somewhat anomalous population at Rannoch, Mid Perth where confirmed specimens were taken by Donisthorpe in 1912 and in more recent years by J Pontin & S Hoy. Flourishing colonies were present on lower slopes of rough grazed meadow in 1996. Other populations are known from Tiree, Eigg and other south western islands and on mainland Kintyre, South Galloway and very locally on sheltered banks as far north as Torridon (Collingwood 1961). The species also occurs in the Channel Islands, the Isles of Scilly, Lundy and the Isle of Man.