Formica rufa (Red Wood Ant)

Another common British ant are those belonging to the species Formica, also known as the’Wood Ant’. Many of these species build huge mounds from pine needles and other woodland litter on the edge of forest clearings or pathways, and can number more than 100,000 members per colony. These ants are large, aggressive, and attack by biting and spraying formic acid very effectively if disturbed.

The largest ant in the UK is Formica sanguinea and is a slave-raider. It raids colonies of other Formicaspecies, such as Formica fusca and steals their brood, taking them back to their own nest where they raise the hatching workers as their own. Surprisingly these ants generally do not kill the workers of the nests they raid unless the defending workers try to stop the invader from taking what it wants. Formica rufa are polygynous and can have hundreds of egg laying queens in one nest.

http://www.lovethegarden.com/pests-diseases/ant-species-and-lifecycle

(sourced 10th September 2012)