Key to Formica cinerea group
Most similar by colony structure and ecology and rather similar in external morphology is the Central Asian F. subpilosa group which differs from the F. cinerea group mainly by smaller eyes and reduced gular and occipital setae numbers.
Setae numbers on different body surfaces are the leading discriminative characters in this species group. Nest sample means of primary (crude) setae data are frequently sufficient for species separation. In discrimination of most similar species, removal of allometric variance and calculation of multiple discriminants as described by Seifert (2002) may be necessary.
Surface characters such as pubescence or microsculpture, as a rule, do not substantially contribute to species separation. The three dimensional structure of microsculpture, however, may serve as accessory discriminator in few cases such as Formica fuscocinerea vs. F. cinerea or F. fuscocinerea vs. F. corsica.
Insignificant interspecific differentiation is also visible in shape of mesosoma or petiole. Formica selysi, the only species with notable deviation in these characters, is much better recognised by its extreme setae characters.
The use of colour pattern as a taxonomic character of the F. cinerea group has a long tradition that is unfortunately maintained (last use e.g. in Petrov & Collingwood 1993 or Czechowski et al. 2002). There is no indication that proportions of reddish and dark pigmentation have any taxonomic value. Concolourous blackish colour morphs and such with increased portion of reddish-brown pigmentation in particular on mesosoma and genae may occur within the same local population of the same species as it was observed in F. cinerea, F. fuscocinerea, F. selysi, and F. georgica. The syntopic occurrence of colour polymorphism suggests it more likely to have a simple genetic basis rather than representing an environmentally induced modification. Geographic zonality in colour morph frequency (e.g. dark morphs dominating in the northern and reddish morphs in the southern and south-eastern parts of the geographic range of F. cinerea) is much better explained by differential selection of genotypes instead of indicating different taxa.
The basic shape and numeric ratios of head such as CL/CW or SL/CS are almost equal in any species of the F. cinerea group which contrasts the situation in the F. fusca or F. rufibarbis group in which notable interspecific differentiation can be found.
Investigation of small-sized nest samples provides the most reliable determination though the majority of individual ants is diagnosable. Any numeric data provided in this simplified key refer to nest sample means of > = 2 individuals. Setae numbers refer to the bilateral sum of the considered body part/s. In difficult cases, use the discriminant functions presented after this dichotomous key.
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- Extensor profile of hind femora with many short, semierect setae: nHFFL > 5. Pyrenees, S France, western and Central Alps, N Italy . . . . . Formica selysi
- Extensor profile of hind femora without or very very few short, semierect setae: nHFFL< 5 . . . . . 2
return to couplet #1
- Whole propodeum including lateral metapleuron with many erect setae: nPR > 28 (excluding setae fringing metapleural gland orifice and those on ventrolateral edge of metapleuron). E Caucasus . . . . . Formica georgica
- Whole propodeum including lateral metapleuron with fewer erect setae: nPR < 28 (excluding setae fringing metapleural gland orifice and those on ventrolateral edge of metapleuron) . . . . . 3
return to couplet #2
- Number of standing setae on underside of head < 3.5. Only Corsica . . . . . Formica corsica
- Number of standing setae on underside of head > 3.5. Outside Corsica . . . . . 4
return to couplet #3
- Number of setae protruding more than 10 mm from margin of petiole scale dorsal of spiracle in caudal or frontal view smaller: nPE 0.7- 10.7; setae projecting dorsad more numerous than those projecting laterad, the latter frequently entirely absent. Microsculpture of lateral mesonotum anterior of metathoracic spiracle in the form of a fine network of much elongated, elipsoid or acutely rhomboid meshes. Inner surface of meshes flat and shining; the ripples of the net are not thicker than 2 mm while the average small diameter of a mesh is about 8 mm - i.e. the ratio of sculptured surface against shining surface is 1 : 4 or smaller (Fig. 2). Eastern and Central Alps, N Apennine . . . . . Formica fuscocinerea
- Number of setae protruding more than 10 mm from margin of petiole scale dorsal of spiracle in caudal or frontal view larger: nPE 9.3- 26.8; setae projecting dorsad as numerous as those projecting laterad; the latter always present. Lateral mesonotum anterior of metathoracic spiracle densely microcarinulate, with a mean carinular crest distance of 4 - 5 mm; mean width of carinulae equal or slightly smaller than width of smooth interspaces (Fig. 1). Palaearctic region from Iberia to 85° E . . . . . Formica cinerea