Key to Palaearctic species in the Formica rufa group

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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.

Key based on Seifert (2021).

1

  • With view on the swivelling plane of the first segment 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 lateral clypeus forming a bead. Medium to large-sized workers usually with whole surface of head, mesosoma and petiole light reddish brown. Formica truncorum group => 2
  • 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

2

  • Iberian Peninsula and Pyrenees => 3
  • Outside Iberian Peninsula and Pyrenees => 4

3

  • Gula and dorsal mesosoma without or with very few setae; nGu + nPn + nPr + nMet < 30 => Formica dusmeti
  • Gula and dorsal mesosoma with more setae; nGu + nPn + nPr + nMet > 30 => Formica frontalis

4

  • 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
  • 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

5

  • Palaearctic with exception of Russian Far East, NE China, Korea, Japan => 6
  • Russian Far East, NE China, Korea, Japan => 12

6

  • 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
  • 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

7

  • 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
  • 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 × Formica rufa
  • 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

8

  • 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
  • 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

9

  • 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
  • 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

10

  • 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
  • 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

11

  • 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
  • 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

12

  • 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
  • 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

13

  • 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
  • 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

14

  • 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
  • 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
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