The Formica rufa group is a subgeneric group within the genus Formica, first proposed by William Morton Wheeler. This group contains the mound-building species of Formica commonly termed "wood ants" or "thatch-mound ants", which build prominent nests consisting of a mound of grass, litter, or conifer needles. The species Formica rufa or the red wood ant is the type species of this subgroup. This particular group can inhabit open deciduous woodlands, dense pine forests, and even moorland. Workers vary in size, the largest reaching about long. They can produce formic acid in their abdomens and eject it in the air when threatened. The only function of males is to mate in flight with queens. Species previously attributed to the Microgyna group were transferred to the F. rufa group by the Wheelers in 1986. Colonies 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. Member species European species include: Formica aquilonia Yarrow, 1955 Formica lugubris Zetterstedt, 1838 Formica paralugubris Seifert, 1996 Formica polyctena Förster, 1850 Formica pratensis Retzius, 1783 Formica rufa Linnaeus, 1761 North American species include: Formica ciliata Mayr, 1886 Formica coloradensis Creighton, 1940 Formica comata Wheeler, 1909 Formica criniventris Wheeler, 1912 Formica dakotensis Emery, 1893 Formica fossaceps Buren, 1942 Formica integra Nylander, 1856 Formica integroides Emery, 1913 Formica laeviceps Creighton, 1940 Formica microgyna Wheeler, 1903 Formica mucescens Wheeler, 1913 Formica obscuripes Forel, 1886 Formica obscuriventris Mayr, 1970 Formica oreas Wheeler, 1903 Formica planipilis Creighton, 1940 Formica propinqua Creighton, 1940 Formica ravida Creighton, 1940 Formica reflexa Buren, 1942 Formica subnitens Creighton, 1940 Asian species Formica yessensis See also Pissant References rufa species group Insect species groups