Key to Nearctic Formica fusca group males

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This worker key is based on: Francoeur, A. 1973. Révision taxonomique des espèces néarctiques du groupe fusca, genre Formica (Formicidae, Hymenoptera). Mémoires de la Société entomologique du Québec. 3:1-316.

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1

  • Metasternum with two pilose processes, arising on each side of the spinasternal cavity (fig. 15, 42); mesometasternal profile composed of a convexity followed by an inverted triangle (fig. 3 3) which is often truncated or rounded at summit . . . . . 2
  • Metasternum without such processes (fig. 195); mesometasternal profile composed of a convexity followed by a straight or concave line (fig. 34-35) . . . . . 10

2

return to couplet #1

  • Mesothoraric episterna without pubescence and punctation at least in the center; surface of polygons made by the microreticulum of these episterna large and shining; eyes smaller, ocular index 38-46; gaster yellow or black; pubescence of gastric dorsum feebly dilute or normal; West of the continent . . . . . Formica subpolita
  • Mesothoracic episterna completely covered by pubescence and punctation; surface of polygons made by the microreticulum of these episterna small and opaque; eyes larger, ocular index over 44 (except in pilicornis, but in this case erect hairs present on eyes); gaster blackish brown to black; pubescence of gastric dorsum dense . . . . . 3

3

return to couplet #2

  • Body pilosity abundant: in particular, erect hairs present on ventral surface of head, occiput, propodeum and all over or nearly so the surface of pronotum; sometimes absent on ventral surface of head of altipetens; cinerea complex . . . . . 4
  • Body pilosity less abundant: erect hairs particularly absent on ventral surface of head, occiput (except sometimes in propatula) and propodeum; limited to the posterior half on pronotum; neoclara complex . . . . . 8

4

return to couplet #3

  • Scapes and eyes with erect hairs; eyes smaller, ocular index 38-45; posteroventral margin of subgenital plate largely emarginate; posterior end of this plate straight (fig. 102-193) . . . . . Formica pilicornis
  • Scapes and eyes without erect hairs; eyes larger, ocular index 44-50; posteroventral margin of subgenital plate not emarginate; posterior end of this plate folded inwardly (fig. 51-52) . . . . . 5

5

return to couplet #4

  • Episterna without erect or suberect hairs; if present, limited to the anteroventral margin of mesothoracic episterna; genae and occipital angles usually hairless, sometimes few hairs near the eyes; erect hairs sometimes absent on ventral surface of head and absent on ventral face of metafemora; West of the continent . . . . . Formica altipetens
  • Episterna with many erect or suberect hairs; gena: with some erect hairs, except on montana in most cases; occipital angles and ventral face of metafemora normally with hairs . . . . . 6

6

return to couplet #5

  • Sides of head less pilose; erect hairs usually limited to occipital angles, but may be present down to the middle of sides; genae usually without erect hairs, sometimes l-2; occipital angles becoming glabrous in the western part of its range; eastern center of the continent . . . . . Formica montana
  • Sides of head more pilose; erect hairs present below the middle of sides; genre with erect hairs . . . . . 7

7

return to couplet #6

  • Body deep brown to blackish brown; scapes shorter, scape index 85-99; dorsal margin of petiole straight or concave; West and western center of the continent . . . . . Formica canadensis
  • Body black; scapes longer, scape index over 99; dorsal margin of petiole convex. Mexico. (Tentatively) . . . . . Formica pulla

8

return to couplet #3

  • Ocelli very large (fig. 139); horizontal length of median ocellus more than 0.48 X the distance between the other two; these ocelli projecting well beyond the occipital margin of head seen in full face; South-west of the continent . . . . . Formica occulta
  • Ocelli smaller (fig. 121, 157); horizontal length of median ocellus less than 0.48 X the distance between the other two; these ocelli not projecting beyond the occipital margin of head seen in full face . . . . . 9

9

return to couplet #8

  • Pronotum more pilose, erect hairs varying from 9 to 23 (mean = 17) and reaching the tegulre; hairs present on petiolar tergite; petiole higher, petiolar index over 48. Mexico . . . . . Formica propatula
  • Pronotum less pilose, erect hairs varying from 6 to 12 (mean = 9) and limited to median half of posterior margin; hairs usually absent on petiolar tergite; petiole lower, petiolar index less than 48; from Yukon to Texas . . . . . Formica neoclara

10

return to couplet #1

  • Thorax more or less shining under a magnification of 25X (surface should be clean); mesoscutellum at least partly shining and shagreened . . . . . 11
  • Thorax usually opaque under a magnification of 25X; mesoscutellum completely opaque and granulose . . . . . 23

11

return to couplet #10

  • Big elongate punctures clearly visible, under a magnification of 50X, between the eye and the insertion of the mandible; pubescence usually dilute on mesothoracic episterna and gastric dorsum; metasternal pilosity abundant and surrounding the spinasternal cavity; neorufibarbis complex . . . . . 12
  • Big elongate punctures, if present, hardly visible between the eye and the insertion of the mandible under a magnification of 50X; pubescence and pilosity diversely combined . . . . . 13

12

return to couplet #11

  • Body pilosity abundant: in particular, erect hairs present on ventral surface of head, occiput, posterior half (or more) of pronotum up to the tegulae (varying from 18 to 36, mean = 27), prosternum, propodeum, mesofemur and dorsal margin of petiole; sometimes absent on ventral surface of head and dorsal margin of petiole; from 4-16 (mean = l3) hairs on the first gastric tergite exclusive of the posterior row; mandibles coarsely striate and punctate . . . . . Formica hewitti
  • Body pilosity reduced: in particular, erect hairs absent on ventral surface of head, occiput, prosternum and limited to median half of posterior margin on pronotum (varying from 8 to 26, mean = 16); if present on propodeum, placed under the spiracle; absent on mesofemora and the first gastric tergite exclusive of the posterior row, sometimes 1-2; mandibles delicately striate and punctate . . . . . Formica neorufibarbis

13

return to couplet #11

  • Body pilosity abundant: in particular, erect hairs present on ventral surface of head and metafemora, occiput, prosternum, propodeum and petiolar tergite; numerous on pronotum and distributed on all its surface or nearly so; West and South of the continent; lepida complex . . . . . 14
  • Body pilosity less abundant: erect hairs particularly absent on ventral surface of head and metafemora (sometimes l-2), occiput, prosternum and propodeum (a few sometimes); less numerous on pronotum and limited to the posterior half of its surface . . . . . 16

14

return to couplet #13

  • Erect or suberect hairs present on the four faces of femora; California. (Tentatively) . . . . . Formica lepida
  • Erect or suberect hairs limited to ventral and lateral faces of femora . . . . . 15

15

return to couplet #14

  • Occipital angles and genre without erect hairs; on episterna limited to the periphery or absent. (Tentatively) . . . . . Formica aerata . . . . . Formica pacifica

16

return to couplet #13

  • Metasternal pilosity less abundant, not surrounding the spinasternal cavity and restricted behind it; pubescence and punctation of mesothoracic katepisterna normal or dense; subsericea complex . . . . . 17
  • Metasternal pilosity more abundant, surrounding the spinasternal cavity; pubescence and punctation of mesothoracic katepisterna dilute; fusca complex . . . . . 20

17

return to couplet #16

  • Petiolar tergite and ventral face of mesofemora usually without erect hairs; on pronotum erect hairs limited to median half of posterior margin and less numerous (mean = 10); few (mean = 2) on the first gastric tergite exclusive of the posterior row; East of the continent . . . . . 18
  • Erect hairs present on petiolar tergite (mean = 9) and usually one on ventral face of mesofemora; numerous on pronotum (mean = 16) and reaching the tegulae; averaging 10 on the first gastric tergite excluse of the posterior row . . . . . 19

18

return to couplet #17

  • Petiole higher, the summit usually overpassing the dorsal border of propodeal spiracle; dorsal margin widely concave or notched; wings blackish; larger species, alitrunk length 3.15- 4.25 mm (mean = 3.61 mm) . . . . . Formica subsericea
  • Petiole lower, the summit usually not reaching the dorsal border of propodeal spiracle; dorsal margin straight or feebly concave; wings paler; smaller species, alitrunk length 3.00 - 3.63 mm (mean = 3.37 mm) . . . . . Formica glacialis

19

return to couplet #17

  • Mandibles narrow, with only an apical tooth (exceptions very rare); scapes usually shorter than head, scape length minus head length varying from - 0.20 to+ 0.05 mm (mean = 0.04 mm) . . . . . Formica argentea
  • Mandibles wide, with normally many teeth; scapes usually longer than head, scape length minus head length varying from - 0.05 to + 0.22 mm (mean = 0.05 mm) . . . . . Formica podzolica

20

return to couplet #16

  • Antero-paracarinal setae longer than 1.3 X the height of frontal triangle; anterior margin of clypeus distinctly angulate; head narrower, cephalic index over 120; postero-ventral margin of subgenital plate widely convexe, posterior end bent upward (fig. 355-356); California . . . . . Formica microphthalma
  • Antero-paracarinal setae shorter than 1.2 X the height of frontal triangle; anterior margin of clypeus convex or weakly angulate; head wider, cephalic index usually less than 120; postero-ventral margin of subgenital plate more or less sinuate and angulate in the middle, posterior end folded inwardly . . . . . 21

21

return to couplet #20

  • Pubescence and punctation very dilute on mesothoracic katepisterna and dilute on gastric dorsum; posterior face of petiolar tergite usually completely devoid of pubescence . . . . . Formica fusca (subrenescens form)
  • Pubescence and punctation feebly dilute on mesothorax katepisterna and normal gastric dorsum; posterior face of petiolar tergite usually with pubescence on the periphery; West of the continent . . . . . 22

22

return to couplet #21

  • Smaller species, alitrunk length usually less than 3.25 mm; scape length less than 1.46 mm (fig. 361); anterior margin of clypeus convex . . . . . Formica fusca (marcida form)
  • Larger species, alitrunk length usually more than 3.25 mm; scape length more than 1.46 mm (fig. 361); anterior margin of clypeus slightly angulate . . . . . Formica accreta

23

return to couplet #10

  • Ventral face of head and mesofemora with erect or suberect hairs . . . . . 24
  • Ventral face of head and mesofemora without erect or suberect hairs . . . . . 25

24

return to couplet #23

  • Mesoscutellum with longitudinal striae; pubescence and pilosity of petiole very long (fig. 475-476); erect hairs longer than 0.4 X the height of petiolar tergite; antero-paracarinal setae of clypeus long; scapes longer, scape length minus head length equal to 0.25 mm, scape index 96 . . . . . Formica sibylla
  • Mesoscutellum without longitudinal strice; pubescence and pilosity of petiole shorter (fig. 448-449); erect hairs shorter than 0.3 X the height of petiolar tergite; antero-paracarinal setce of clypeus short; scape shorter, scape length minus head length equal to 0.07 mm, scape index 90; Mexico . . . . . Formica subcyanea

25

return to couplet #23

  • Posterior end of subgenital plate straight (fig. 420-421); dorsal margin of petiole convex; ocular index less than 47 (fig. 442) . . . . . Formica foreliana
  • Posterior end of subgenital plate bent upward (fig. 436-437); dorsal margin of petiole concave or notched; ocular index over 47 (fig. 442) . . . . . Formica gnava