Key to Palaearctic Formica rufa group species

This worker key is based on: Stockan, J., E. Robinson, J. Trager, I. Yao, and B. Seifert, B. 2016. Introducing wood ants: Evolution, phylogeny, identification and distribution. In J. Stockan and E. Robinson (Eds.), Wood Ant Ecology and Conservation. pp. 1-36. Cambridge: Cambridge University Press. doi:10.1017/CBO9781107261402.002

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 * Formica
 * Wood Ants
 * Formica species groups

1

 * Posterior margin of head clearly excavated and with pronounced occipital corners (Figure 1.3); with maximum median head length in focal plane, depth of excavation 4.9–9.6% of CW. Posterior (basal) edge of mandibles near to the cutting edge with 1–3 accessory denticles . . . . . Subgenus Coptoformica


 * Posterior margin of head convex, straight or only weakly excavated. Lateral occiput without pronounced corners (Figures 1.4 and 1.5). Posterior edge of mandible without denticles . . . . . 2

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 * Anteromedian clypeal margin clearly emarginate (Figure 1.5) . . . . . Subgenus Raptiformica


 * Anteromedian clypeal margin not emarginate (Figure 1.4) . . . . . 3

3
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 * Frontal triangle significantly more shining than adjacent surfaces . . . . . Subgenus Formica s.str 5


 * Reflexion properties of frontal triangle not contrasting to those of adjacent surfaces. Frontal triangle in most species matt; if shining, then whole dorsal head, mesosoma and gaster also shining . . . . . 4

4
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 * Scape rather short and thick, SL/CW<0.960. Pigmentation characteristic: whole head, pronotum, gaster and occasionally dorsal mesonotum blackish; remaining mesosoma reddish brown. Whole body matt, posterior margin of head and propodeum without standing setae . . . . . Formica uralensis


 * Scape long and slender, SL/CW>0.960. Pigmentation pattern deviating . . . . . Subgenus Serviformica

5
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 * 2nd and 3rd funiculus segments at least twice as long as wide (Figure 1.6). Middle part of lateral clypeus more deeply depressed than in F. rufa. Typical pigmentation in medium-sized to large workers: whole head, mesosoma and petiole light reddish brown (specimens with pigmentation reminiscent of F. rufa are rare), Formica truncorum complex. All following numeric data are nest means . . . . . 6


 * 2nd and 3rd funiculus segments less than twice as long as wide (Figure 1.7). Middle part of lateral clypeus less deeply depressed (F. rufa may serve as standard for group 5b; however, the hind portion of lateral clypeus may be as deeply depressed as in truncorum!). Dorsal vertex almost always with blackish pigmentation. All following numeric data are nest means #|. . . . . 9

6
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 * Posterior head without standing setae, whole surface of mesosoma without or only very few, short setae, underside of head with few setae, nCU<7, Iberia only . . . . . Formica dusmeti


 * Posterior head with standing setae, whole surface of mesosoma with numerous setae, underside of head with many setae, nCU>7 . . . . . 7

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 * Iberia, Tibet to NE China and N Japan. Dorsal plane of scape without or only occasional short setae, nSc 0–3 . . . . . 8


 * Other regions: temperate to boreo-montane zone of Palaearctic from 5°E to 143°E. Dorsal plane of scape usually with several to many standing setae,nSc 2–27. Sympatric with yessensis in Hokkaido, differs here from the latter by more developed pilosity on dorsum of scape and underside of head (nSC>2, nCU >30). Sympatric with sinensis in NE China, differs here from the latter by longer hairs on eyes (EyeHL> 15 μm) and more profuse pilosity on hind margin of head (nCH>25) . . . . . Formica truncorum

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 * Tibet to NE China. Eyes without or with minute hairs, EyeHL 0–15 μm. Underside of head with profuse setae, nCU 13–39 . . . . . Formica sinensis


 * North Japan.Eyes with significantly longer hairs,EyeHL 10–35 μm. Underside of head with less profuse setae, nCU 9–27 . . . . . Formica yessensis


 * Iberia. Eyes with significantly longer hairs, Eye HL 1–35 μm. Underside of head with less profuse setae, nCU 9–27. . . . . Formica frontalis

9
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 * With maximum median CL in focal plane, posterior contour of head hairless. In very hairy F. rufa, nCH occasionally reaching 3.6, with 15–60 μm long hairs, but then nPn >20 and SL/SMAX 10.13 ± 0.29 . . . . . 10


 * With maximum median CL in focal plane, contour of head from median occiput to anterior eye margin with >3 setae. In weakly haired F. aquilonia, nCH occasionally falling to 1.3, but then nPn <13 and SL/SMAX 9.28 ± 0.23 . . . . . 11

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 * Weakly haired: nCU 0.1–3.0, CUHL 7–97 μm, nPN 0.1–5.6, mPnHL 6–55 μm, nPR 0–5.2, nCH 0–0.9 (setae minute). Scape rather slender: SL/SMAX 10.00 ± 0.24 . . . . . Formica polyctena


 * Moderately hairy: nCU 1.9–6.6, CUHL 96–197 μm, nPN 5.8–16.0, mPNHL 47–83 μm, nPR 4.4–11.2, nCH 0–1.2 (setae minute). Scape rather slender: SL/SMAX 10.00 ± 0.24 . . . . . Formica rufa × Formica polyctena hybrid


 * More strongly haired: nCU 5.1–11.0, CUHL 155–224 μm. nPN 12.5–45.0, mPnHL 61–102 μm, nPR 8.5–25.1, nCH 0–3.6 (setae small). Scape rather slender: SL/SMAX 10.13 ± 0.29 . . . . . Formica rufa

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 * Discriminant 0.050∗nCH +0.034 MetHL –5.113<0. Longest propodeo-metapleural hair below level of propodeal spiracle shorter: MetHL 0–142 μm.With maximum median CL in focal plane, contour of head from median occiput to anterior eye margin with fewer setae: nCH 1.3–12.3 (F. opaca is similar in nCH but differs by much longer gular and mesosomal setae: CUHL>175 μm, mPnHL>80 μm, MetHL>175 μm). In Central Europe only in the mountains between 550 and 2100 m a.s.l. and in the Alps westwards to 9°E (reports of occurrences farther west on mainland Europe should be checked) . . . . . Formica aquilonia


 * Discriminant 0.050∗nCH +0.034 MetHL –5.113>0. Longest propodeo-metapleural hair below level of propodeal spiracle longer: MetHL 134–237 μm. With maximum median CL in focal plane, contour of head from median occiput to anterior eye margin with more setae: nCH 4–65 . . . . . 12

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 * Number of setae on underside of head, sides of mesopleuron and lower propodeum metapleuron smaller: nCH 4–8, nMet 2–5. Russian Far East (Ussuria) . . . . . Formica opaca


 * Number of setae on underside of head and sides of lower propodeum/metapleuron larger: nCH 5–62, nMet 4–21 . . . . . 13

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 * Scape more compact: SL/SMAX 8.45–10.07. Frons appearing 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 anterolaterally from mid-ocellus. Generally boreo-montane species. Discriminant for entire western Palaearctic [with CS in mm] –0.355 CL/CW–6.909 SL/CS+3.06 SL/SMAX–10.774 PEW/CS+0.418 CS–19.5<0 . . . . . 14


 * Scape slender: SL/SMAX 9.94–11.74. Frons matt. This overall impression is produced by a stronger more reticulate microsculpture. More xerothermic, woodland and woodland–steppe habitats. Discriminant for entire western Palaearctic [with CS in mm] –0.355 CL/CW–6.909 SL/CS+3.06 SL/SMAX–10.774 PEW/CS+0.418 CS–19.5>0 . . . . . Formica pratensis

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 * Only western Alps, ranging east to approximately 11°E. Pronotal setae shorter: mPNHL 61–93 μm. Propodeo-metapleural area below level of propodeal spiracle with fewer and shorter setae: nMet 3.3–9.7, MetHL 130–174 μm. Discriminant 0.068 mPNHL +0.011 MetHL +0.465 nMET +0.83 SL/SMAX +19.004 CL/CW −15.207 SL/CS 7.13 PEW/CS −0.028 nSC −0.227 nCH −14.437<0 . . . . . Formica paralugubris


 * Pronotal setae longer: mPNHL 79–127 μm. Propodeo-metapleural area below level of propodeal spiracle with more and longer setae: nMet 6.5–14.8, MetHL 153–225 μm. Discriminant 0.068 mPNHL +0.011 MetHL +0.465 nMET +0.83 SL/SMAX +19.004 CL/CW −15.207 SL/CS −7.13 PEW/CS −0.028 nSC −0.227 nCH −14.437>0 . . . . . Formica lugubris