Southern Wood Ant

Nests of these ants are large, conspicuous, dome-shaped mounds of grass, twigs, or conifer needles, often built against a rotting stump and usually situated in woodland clearings where the sun's rays can reach them. Large colonies may have 100,000 to 400,000 workers and 100 queens. F. rufa is highly polygynous and often readopts postnuptial queens from its own mother colony, leading to old, multichamber nests that may contain well over 100 egg-producing females. These colonies can be several metres in height and diameter. F. rufa is aggressively territorial, and often attacks and removes other ant species from the area. Nuptial flights take place during the springtime and are often marked by savage battles between neighbouring colonies as territorial boundaries are re-established. New nests are established by budding from existing nests in the spring, or by temporary social parasitism, the hosts being species of the F. fusca group, notably F. fusca and F. lemani, although incipient F. rufa colonies have also been recorded from nests of F. glebaria and F. cunicularia. An F. rufa queen ousts the nest's existing queen and lays eggs of her own, and the existing workers care for her offspring until those offspring take over the nest.

These ants' primary diet is aphid honeydew, but they also prey on invertebrates such as insects and arachnids; they are voracious scavengers. Foraging trails may extend 100 m (330 ft). Larger workers have been observed to forage farther away from the nest. F. rufa is commonly used in forestry and is introduced into an area as a form of pest management.