Formica aquilonia

Identification
Bicoloured with dark markings on head and promesonotum varying in size and intensity - generally not as brightly coloured or as large as Formica rufa. In the typical form distinct outstanding hairs fringe the posterior border of the head but do not occur forward towards the eyes as in Formica lugubris. In many samples from South Norway and South Finland these hairs may be hard to find or absent. Erect hairs on gula and dorsum of alitrunk variable, usually short and sparse. Eyes with distinct short hairs but much less prominent than in F. lugubris. Frons rather dull with close dense microsculpture, gaster very closely punctured. Suberect hairs on extensor surfaces of hind femora and tibiae always present but sometimes few. Antennal scapes bare. Head width of largest workers less than 2 mm. Length: 4.0-8.5 mm (Collingwood 1979).

Distribution
Eastern Alps to Siberia, North Italy to North Norway (Collingwood 1979).

Distribution based on Regional Taxon Lists
Palaearctic Region: Austria, Belarus, Bulgaria, China, Czech Republic, Democratic Peoples Republic of Korea, Denmark, Estonia, Finland, France, Georgia, Germany, Italy, Latvia, Lithuania, Mongolia, Montenegro, Norway, Poland, Romania, Russian Federation, Serbia, Slovenia, Sweden, Switzerland, Ukraine, United Kingdom of Great Britain and Northern Ireland.

Biology
Collingwood (1979) - This is undoubtedly the commonest wood ant in Fennoscandia. Large tracts of forest in the centre and north are dominated by this species which is usually found in large multicolonial groups with isolated nests being very rare. This is one of the least aggressive species of the F. rufa group. Long compact trails radiate from each nest to other nests or to aphid bearing trees and antagonism between neighbouring nests has not been observed. In South Norway and South Finland comparative hairlessness in many populations makes for confusion with the rather similar F. polyctena. Usually, however, if enough workers are collected a majority of at least 60 % of individuals will be found to have some projecting hairs at the back of the head.

However there is a form of this species found locally in the western suburbs of Helsinki to the Sjuntio district of Ab, within an area of about 40 km by 10 km, which is almost completely hairless in all parts of the body given as species specific by Yarrow (1955) for F. aquilonia. All castes moreover tend to be somewhat larger and more brightly coloured. This could well be a subspecies or species in the making. Its foraging habits have been studied by Rosengren (1971, 1977a, 1977b) under the name of Formica polyctena. This consistent degree of hairlessness has not been found elsewhere within the range of F. aquilonia, except perhaps in Esthonia, according to samples sent to H. Wuorenrinne by Professor V. Maavara.

The characteristics are as follows: only about 5 % or fewer workers in a series have an indication of short hairs projecting from the occipital comers of the head. Queens have no such hairs but occasional microscopic hairs have been detected on the basal face of the gaster in a very few specimens of about 50 examined. In the few males examined only 1 in 12 has projecting genal hairs. The reasons for retention as an infraspecific form of F. aquilonia include the close sculpturing of the worker frons, small eye hairs which are always present as in F. aquilonia while hairs on the extensor surface of the femora form a more or less close fringe as in F. aquilonia in a majority of the workers. The queen, which appears more brilliant than F. aquilonia, has extremely close micropunctures on the gaster as in that species (and in this character alone is quite unlike F. polyctena) while the male has fringing femoral hairs although specimens are also somewhat larger and more shining than F. aquilonia.

Nomenclature

 * schmidti. Formica rufa subsp. schmidti Ruzsky, 1926: 109 (w.) RUSSIA. [First available use of Formica rufa subsp. rufa var. schmidti Ruzsky, 1920: 78; unavailable name.] [Junior primary homonym of †schmidtii Heer, 1849: 138, above.] Synonymous with aquilonia: Dlussky, 1967a: 90, hence aquilonia the first available replacement name.
 *  aquilonia. Formica aquilonia Yarrow, 1955a: 31 (diagnosis in key), figs. 21, 25, 29, 33, 37, 41, 45, 49, 53, 57, 61, 65 (w.q.m.) GREAT BRITAIN. Synonymous with schmidti Ruzsky, 1920: 78 [Junior primary homonym of †schmidtii Heer, 1849: 138.]: Dlussky, 1967a: 90 and hence first available replacement name. See also: Kutter, 1977c: 271; Kupyanskaya, 1986a: 98; Gösswald, 1989: 19; Kupyanskaya, 1990: 197; Atanassov & Dlussky, 1992: 276.