Formica aquilonia YARROW 1955

Formica aquilonia YARROW, 1955

Formica aquilonia YARROW, 1955 [description, photo of holotype, zoogeography]

This taxon was described from Black Wood of Rannoch, Pertshire, Scotland (56.667° N, 4.347° W). YAR- ROW (1955)’s description of gynes and workers, the pictures of the holotype gyne in AntWeb (ANTWEB 2021) (CASENT0903277), and the geographic position of the type locality unquestionably indicate the identity of this taxon.

All material examined. Numeric phenotypical data were recorded in 81 nest samples with 381 workers and 30 gynes. These originated from Austria (17 samples), Czechia (three), Finland (24), Scotland (one), Mongolia (five), Norway (three), Russia (19), Sweden (one), and Switzerland (eight). For details, see SI1, SI2, and SI3. The total number of samples numerically or subjectively investigated was 130.

Geographic range. Eurosiberian-boreomontane. Continuous range from Northern Ireland and Scotland to East Siberia (131° E), in Fennoscandia between 56.3 and 71° N, and in Siberia between 47.5 and 63° N. The montane range in Europe extends from SE to NW over the Rila Mountains, NW Carpathians, Bohemian Forest, and the Eastern Alps westward to 9° E. In the Alps ascending to 2400 m. Main distribution in the Alps within the autochthonous distributional area of Larix (EICHHORN 1964).

Diagnosis of worker (Tab. 2, key). Small; mean and maximum CS over all social types 1575 and 1902 µm. Scape short and rather thickset, SL / CS 1750 0.908, SL / Smax 1750 9.25. Setae on eyes rather short, EyeHL 1750 24 µm; setae on dorsal plane of scape usually absent or few, nSc 1750 usually 0 - 2; head margin behind eyes with few short setae which usually concentrate at the occipital corners, nCH 1750 5.1, OccHL 1750 64 µm; gular, pronotal, and propodeal setae sparse and rather short, nPn 1750 7.9,mPnHL 1750 42µm, nPr 1750 5.8; seta on lateral mesopleuron more numerous but on lateral metapleuron absent or very few and of moderate length, nMes 1750 14.7, nMet 1750 1.8, MetHL 1750 86µm.

Diagnosis of gyne (Tab. 6, Fig. 8). Small; mean and maximum CS 2015 and 2173 µm. Scape short and thickset, SL / CS 0.810, SL / Smax 8.32. Setae on eyes rather short, EyeHL 29 µm; head margin behind eyes with very few short setae which usually concentrate at the occipital corners, nCH 2.1, OccHL 30 µm; gular, pronotal, mesopleural, and metapleural setae and those on frontal face of first gaster tergite few and rather short, nGu 3.1, GuHL 51 µm, PnHL 43 µm, nMes 2.5, nMet 1.4, MetHL 30 µm, nGfr 8.1, GfrHL 64 µm. Margin of petiole scale above spiracle with few short setae. Pigmentation without peculiarities. Dorsum of gaster shiny but less than in Formica rufa; foveolae on first gaster tergite more dense, FodG 27.7 µm.

Taxonomic comments and clustering re-sults. Results of clustering are shown and commented in section “ Formica aquilonia × polyctena – hybrids and backcrosses” (p. 156). Frequent hybridization and introgression raise the question if F. aquilonia and Formica polyctena can be considered as separate species. One option would be to reduce them to subspecies with differing climatic adaptations – boreo-montane and frost-hardy in F. aquilonia, and temperate-planar-colline and less frosthardy in F. polyctena. I advocate here, for operational and pragmatic reasons, to stay with a nomenclatorial treatment as different species. Reticulate evolution in the Formica rufa group as a whole already produces a diffi- cult taxonomic situation which would be further complicated if we abandon the parsimonious binary naming. A third, radical solution, synonymizing F. aquilonia with F. polyctena and then, as a logical consequence (see section “ Formica rufa LINNAEUS, 1761 ”, p. 152), synonymizing these two taxa also with F. rufa, causes more problems than it solves. Speaking only of F. rufa would cause a loss of information on the structure of biodiversity and on the natural history of its elements. For hybridization with Formica lugubris and Formica paralugubris, see sections “Hybrids Formica aquilonia × lugubris ” (p.152) and “Hybrids Formica aquilonia × paralugubris ” (p.156).

Habitat and biology. See the species profile in SEIFERT (2018).