This is one of eleven British ant species in the genus Formica but it is the only one of the sub-genus Raptiformica. This is a predominantly Nearctic group and F. sanguinea is the only species with a Palaearctic distribution. Superficially similar to Wood ants of the Formica rufa-group, F. sanguinea is distinguished by being the only British Formica showing dulotic behaviour. It is commonly known as the blood-red slave-making or robber ant. This reflects its habit of raiding nests of other ants, particularly those in the Formica fusca-group (Serviformica) and removing their larvae and pupae. Some are eaten but others are raised in the parent nest as auxiliary workers. In the field, large workers of F. sanguinea (reaching 9 mm) are characteristically bright red with slate grey gasters. They may be distinguished from Wood ants by a median anterior notch in their clypeus and the fact that they seldom raise their gaster forward between their legs to eject formic acid. Gynes are similar to the workers, and males are distinguishable from those of other Formica species by their prominent mandibular dentition as well as an excised clypeal border.
F. sanguinea has a disjunct British distribution, predominating in southern England and central Scotland, with scattered records on the Welsh borders. It is not found in Ireland. Its southern distribution is closely aligned to sandy soil geology, particularly the Lower Greensands and Bagshot Beds of Surrey, Sussex and Hampshire. In Scotland it is mainly found around the Spey and Dee valleys.