Wood ants are social insects that live in very large colonies. Most of the individuals found in these colonies are non-reproductive females known as workers. These individuals carry out the foraging and brood-care duties for the colony. The queen is the only member of the colony to lay eggs (3). At the beginning of spring each year, unfertilised eggs are produced, and these develop into males. Other eggs that are produced at this time and are fed more become queens, while others develop as workers. During June, usually on a warm humid day, huge numbers of winged reproductive males and queens leave the nest en masse and engage in a mating flight known as the ‘nuptial flight’. After mating the male soon dies, the queen sheds her wings, and searches for a suitable location to establish a new nest (6). She will not mate again during her lifetime, but stores sufficient sperm inside her body to fertilise all her future eggs (3).
Scottish wood ants create very large dome-shaped nests that are ‘thatched’ with pine needles. These nests typically have one elongated side, to maximise the sunlight falling on the colony (3). Ants are known to have very close mutually beneficial associations with many other types of organism (8), and it has recently been discovered that the nests of the Scottish wood ant contain many earthworms (Dendrodrilus rubidus). It is thought that the earthworms benefit from this association as the nests provide a relatively warm, constant habitat, and the ants benefit in turn as the earthworms keep the nest free of damaging moulds and fungi (9).
Wood ants are carnivorous, and workers carry a wide variety of prey back to the nest along trails that extend throughout the territory. The workers also tend aphids for the sugary ‘honeydew’ that they exude from the anus; the aphids gain protection from predators in return for this service (6). Studies in Scotland have shown that each F. aquilonia worker brings an average of one and a half times its own weight in food back to the nest daily. Five to six trackways leave each nest and lead to the trees where most of the foraging takes place. Many workers may leave the trackways to forage in the surrounding area at random (7).