Formica rufa, LINNAEUS, 1761

Seifert, Bernhard, 2021, A taxonomic revision of the Palaearctic members of the Formica rufa group (Hymenoptera: Formicidae) - the famous mound-building red wood ants, Myrmecological News 31, pp. 133-179 : 140-141

Key to the workers of the Palaearctic Formica rufa group:

This key can certainly solve a good number of determinations in a rather simple way but the best results are achieved when own discriminant functions are run using the data of SI1 as reference. In contrast to Tables 1 - 5 and for more simplicity, this key works with primary, not allometrically corrected data, and all linear measurements are given in mm. Because of the enormous intraspecific and intranidal variation, nest sample means should be considered in critical cases. The percentage of reddish pigmentation follows a positive allometric trend and is of rather little indicative value. Figures 5-20 with z-stacking photos of the species from different viewing positions are presented after the key.

1a With view on the swivelling plane of the first seg- ment of antennal funiculus, ratio of median length of second funiculus segment against its maximum width ≥ 2.0 (movement within only a swivelling plane is defined by the hinge joint of distal scape with the first funiculus segment). Lateral clypeus deeply depressed, as result anterior portion of lat- eral clypeus forming a bead. Medium to large-sized workers usually with whole surface of head, meso- soma and petiole light reddish brown. Formica truncorum group ...................................................... 2

1b Ratio of median length of second funiculus segment against its maximum width <2.0. Lateral clypeus less deeply depressed and anterior portion of lateral clypeus not forming a bead. Percentage of surface with dark or blackish brown pigmentation usually larger .......................................................................... 5

2a Iberian Peninsula and Pyrenees ............................... 3

2b Outside Iberian Peninsula and Pyrenees ................. 4

3a Gula and dorsal mesosoma without or with very few setae; nGu + nPn + nPr + nMet <30 .............. ..................................................... Formica dusmeti

3b Gula and dorsal mesosoma with more setae; nGu + nPn + nPr + nMet> 30 .......... Formica frontalis

4a More hirsute on all body positions. Discriminant 76.03 * EyeHL + 0.073 * nCH-0.057 * nGu + 0.08 * nMet + 12.36 * mPnHL - 14.75 * MetHL - 1.33> 0 (error 0% in 92 individuals, Tab. 5) ................. ............................................... Formica truncorum

4b Less hirsute on all body positions. Often a disparity between rather few setae on dorsal mesosoma and rather many setae on gula is visible. Discriminant <0 (error 0% in 70 individuals, Tab.5). Only E Tibet and China. .................................. Formica sinensis

5a Palaearctic with exception of Russian Far East, NE China, Korea, Japan.................................................. 6

5b Russian Far East, NE China, Korea, Japan........... 12

6a Hind margin of head without or only occasional small setae, nCH 0 - 1; if nCH is slightly larger, then scape slender with SL / Smax 10.08 ± 0.39. Eyes with only short microsetae, EyeHL 0.020 ± 0.004. Mesopleuron with rather few setae, nMes 10.5 ± 7.4. Discriminant 0.024 * nCH + 0.08 * nMes - 0.046 * nPr - 11.451 * SL + 72.20 * Smax + 62.96 * EyeHL + 3.879 <0 (error 0% in 114 nest sample means) ........................................................................ 7

6b Hind margin of head usually with many setae, nCH> 1; if nCH is near zero (occasional in F. aquilonia ), then scape thickset with SL / Smax 9.27 ± 0.34. Eyes with longer microsetae, EyeHL 0.030 ± 0.008. Mesopleuron with rather many setae, nMes 21.6 ± 10.4. Discriminant> 0 (error 1.7% in 180 nest sample means) ........................................................... 8

7a Weakly haired; nest means: nGu 0.1 - 3.0, GuHL 0.007 - 0.097, nPn 0.1 - 5.6, mPnHL 0.006 - 0.055, nPr 0 - 5.2, nCH 0 - 0.9 (microsetae) ..................... ................................................. Formica polyctena

7b Moderately hairy; nest means: nGu 1.9 - 6.6, GuHL 0.096 - 0.197, nPn 5.8 - 16.0, mPnHL 0.047 - 0.083, nPr 4.4 - 11.2, nCH 0 - 1.2 (microsetae) ................ .................................... Formica polyctena × rufa

7c More strongly haired; nest means: nGu 5.1 - 11.0, GuHL 0.155 - 0.224, nPn 12.5 - 45.0, mPnHL 0.061 - 0.102, nPr 8.5 - 25.1, nCH 0 - 3.6 (setae small)... ........................................................... Formica rufa

8a Longest propodeo-metapleural hair below level of propodeal spiracle shorter: MetHL 0 - 0.142. With maximum CL in focal plane, contour of head from median occiput to anterior eye margin with fewer setae: nCH 1.3 - 12.3. In doubtful cases: discriminant 0.0503 * nCH + 22.213 * MetHL -3.481 <0 (error 0% in 75 nest samples) .......................... ................................................... Formica aquilonia

8b Longest propodeo-metapleural hair below level of propodeal spiracle longer: MetHL 0.134 - 0.237. With maximum CL in focal plane, contour of head from median occiput to anterior eye margin with more setae: nCH 5.2 - 65.2. Discriminant> 0 (error 0% in 305 nest samples) ............................................ 9

9a Scape more compact: SL / Smax 8.45 - 10.07. Frons appears at low magnification not perfectly matt, with a mild silky shine. This overall impression is produced by a weaker microsculpture with more longitudinal and less reticulate elements, particularly along the frontal line and anteriolaterally from mid ocellus. With all measurements in mm, discriminant 2.524 - 3.89 * CW - 12.25 * SL + 5.889 * PeW + 117.36 * Smax> 0 (error 0% in 291 nest samples for whole Palaearctic range). Boreo-montane species ............................................................. 10

9b Scape slender: SL / Smax 9.94 - 11.74. Frons matt. This overall impression is produced by a stronger more reticulate microsculpture. Discriminant <0 (error 0% in 94 nest samples for whole Palaearctic range). More xerothermous woodland and woodland-steppe habitats ................ Formica pratensis

10a Only W Alps, ranging east to approximately 11° E. Pronotal setae shorter: mPnHL 0.061 - 0.093. Propodeo-metapleural area below level of propodeal spiracle with fewer and shorter setae: nMet 3.3 - 9.7, MetHL 0.130 - 0.174. Discriminant 48.8 * mPnHL + 16.6 * MetHL - 0.100 *nCH + 0.087 * nMet - 0.072 * nSc - 5.535 <0 (error 0% in 70 nest sample means of four individuals, function only valid for Central Europe) ...................................................... .......................................... Formica paralugubris

10b Widely distributed. Pronotal setae longer: mPnHL 0.079 - 0.127; nMet 6.5 - 14.8, MetHL 0.153 - 0.225. Discriminant> 0 (error 3.1% in 98 nest sample means of four individuals; function only valid for Central Europe........................................................ 11

11a Whole Palaearctic. Population from the Alps poorly separable from F. helvetica sp.n. Discriminant 36.64 * Smax + 0.128 * nMet + 0.110 * nSc + 0.068 * nCH - 53.54 * mPnHL - 3.224> 0 (error 20.5% in 380 individuals and 14.6% in 89 nest samples) ..................................... Formica lugubris

11b Only known from a local population in Mingèr Valley in the Eastern Swiss Alps. Separation from F. lugubris very weak. Discriminant 36.64 * Smax + 0.128 * nMet + 0.110 * nSc + 0.068 * nCH - 53.54 * mPnHL - 3.224 <0 (error 13.3% in 30 individuals and 11.1% in nine nest samples) ............................ ......................................... Formica helvetica sp.n.

12a Gula, mesopleuron, propodeum and metapleuron with many setae; nGu + nMes + nPr + nMet = 38 - 110. Discriminant 0.092 * nGu + 0.048 * nMes + 0.235 * nMet + 0.051 * nPr - 3.8554> 0 (error 4.9% in 161 individuals and 0% in 44 nest samples) ..... .................................................... Formica lugubris

12b Gula, mesopleuron, propodeum and metapleuron with fewer setae; nGu + nMes + nPr + nMet = 3 - 46. Discriminant <0 (error 0.9% in 424 individuals and 0% in 95 nest samples) ............................................ 13

13a Gular setae much longer, GuHL 0.217 ± 0.021; setae in all other body positions longer. Mesopleuron with fewer setae, nMes 6.6 ± 2.1. Discriminant 20.041 * GuHL + 30.455 * mPnHL + 2.661 * MetHL - 0.147 * nMes - 4.466> 0 (error 0% in 38 individuals). Ussuri region ....... Formica kupyanskayae

13b Gular setae much shorter, GuHL 0.098 ± 0.033; setae in all other body positions shorter. Mesopleuron with more setae, nMes 13.3 ± 4.9. Discriminant <0 (error 0% in 386 individuals) ........................... 14

14a Dorsal plane of scape and hind margin of head with rather many setae, nSc 10.5 ± 4.3, nCH 9.8 ± 4.2. Metapleuron with rather long setae, MetHL 0.133 ± 0.029. Discriminant 6.56 * PeW - 11.58 * Smax - 3.155 * CW + 0.013 * nCH + 0.357 * nSc + 3.505 * MetHL - 1.224> 0 (error 9.8% in 41 individuals and 0% in 10 nest sample means). Ussuri and Sichote Alin range .................. Formica ussuriensis sp.n.

14b Dorsal plane of scape and hind margin of head with very few setae, nSc 0.3 ± 1.3, nCH 4.3 ± 3.8. Metapleuron with short setae, MetHL 0.074 ± 0.047. Discriminant <0 (error 1.0% in 102 individuals and 0% in 31 nest sample means) ............. .................................................. Formica aquilonia

Figures

Figs.5-13: (5-ussu) Formica ussuriensis sp.n., worker, holotype, head. (6-ussu) Formica ussuriensis sp.n., worker, holotype, lateral.(7-ussu) Formica ussuriensis sp.n., gyne, head; note the more trapezoid headshape.(8-aqui) Formica aquilonia, gyne, head; note the more rounded head shape.(9-prat) Formica pratensis, worker, neotype, head; note the more reticulate microsculpture of central vertex compared with Formica lugubris (Figs.14, 15), producing a matt surface appearance.(10-prat) Formica pratensis, worker, neotype, lateral aspect. (11-prat) Formica pratensis, gyne, P morph, lateral; almost no setae on head, mesosoma, and first gaster tergite. (12-prat) Formica pratensis, gyne, N morph, lateral; many setae on head, mesosoma, and first gaster tergite. (13-kupy) Formica kupyanskayae, gyne, head.

Figs.14-20: (14-lugu) Formica lugubris, worker, normal morph, head; central vertex suggestedly shiny due to weaker transverse microsculpture. (15-lugu) Formica lugubris, worker, Hippie morph, head; central vertex suggestedly shiny due to weaker transverse microsculpture. (16-helv) Formica helvetica sp.n., worker, holotype, head. (17-helv) Formica helvetica sp.n., worker, holotype, lateral. (18-trun) Formica truncorum, worker, head. (19-trun) Formica truncorum, gyne, head. (20-sine) Formica sinensis, worker, lateral; note the contrast between weak pronotal and strong gular pilosity.