The genetic relationships in
F. rufa group colonies can be complex. Colonies can be polygynous (having multiple queens) and these are often polydomous (having multiple nests per colony). Queens may be singly or multiply mated, and in polygynous colonies, may or may not be related. Colonies are rarely, if ever, independently formed. They either bud off from existing colonies, or are formed by temporary
social parasitism of colonies of
F. fusca or other closely related species. A wood ant queen ousts the existing queen, lays eggs, and the
F. fusca workers raise her offspring until the nest is taken over. Some species in the
F. rufa group sometimes form enormous "supercolonies" consisting of hundreds or thousands of nests. The largest documented example is an
F. yessensis colony in Japan covering containing an estimated 306 million workers and 1 million queens.{{cite book ==Member species==