Key to Lasius Palaearctic workers

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This worker key is based on: Wilson, E. O. 1955. A monographic revision of the ant genus Lasius. Bulletin of the Museum of Comparative Zoology. 113:1-201.

Wilson noted - Excludes Lasius buccatus Starcke and Lasius orientalis, members of the subgenus Dendrolasius known only from sexual forms; see key to the queens.

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Lasius (this genus page provides links to other Lasius keys).

1

  • Maximum worker eye length 0.20 X the head width or more . . . . . 2
  • Maximum worker eye length 0.17 X the head width or less . . . . . 6

2

return to couplet #1

  • In workers with HW 0.79-1.21 mm., the 81 ranges 82-94 and is usually 91 or less; alitrunk and petiole homogeneous light reddish brown, contrasting against the dark brown gaster; scapes and tibiae lacking standing hairs and usually hairs of any inclination; body pilosity sparse, the curving portion of the occipital corners viewed in full face typically devoid of hairs, rarely with one or two; males large, HW 1.04-1.10 mm. in three nest series examined; mandible with a shallow cleft separating the anterior and posterior halves of the masticatory border . . . . . Lasius brunneus
Lasius brunneus casent0172717 profile 1.jpg
  • In workers with HW 0.79-1.21 mm., the 81 is 95 or more; body coloration variable, rarely exactly as in brunneus; scapes and tibiae often with standing hairs; curving portion of occipital corners usually with two or more standing hairs; males with HW rarely greater than 1.04 mm., usually less than 1.00 mm.; mandible lacking a clear-cut cleft on the masticatory border . . . . . 3

3

return to couplet #2

  • In workers with HW 0.86-1.12 mm., the 81 ranges 112-124; if outside this HW range, then the 81 should fit an extrapolation of the SI-HW regression zone (Japan) . . . . . Lasius productus
Lasius productus casent0903217 p 1 high.jpg
  • Within the same worker HW range, 81 does not exceed 109 and is usually much less . . . . . 4

4

return to couplet #3

  • The worker possessing at least one and usually both of the two following characters: (1) alitrunk and petiole yellowish red, contrasting with the medium to dark reddish brown head and gaster (body tending to concolorous reddish brown in the Balkans area; see under geographic variation of this species); (2) scape with numerous preponderantly subdecumbent hairs. In addition, 81 is 103-109 within a HW range of 0.61-1.10 mm. (Europe) . . . . . Lasius emarginatus
Lasius emarginatus casent0172762 profile 1.jpg
  • Worker body concolorous reddish brown to blackish brown; within the range of emarginatus in Europe, the scape either lacks standing hairs or these are preponderantly suberect-erect. In all populations of alienus except that in the Balkans area, and in all of niger except those in North Africa, the Balearics, the Atlantic Islands, and eastern Asia, the 81 is 95-103 within a HW range of 0.61-1.10 mm. . . . . . 5

5

return to couplet #4

  • In workers with PW 0.53-0.70 mm., scapes and tibiae with few or no standing hairs, the seta count (see under Terminology and Measurements) always less than 20 and usually less than 10. . . . . . Lasius alienus
Head of Lasius alienus worker
Profile of Lasius alienus worker
  • Within the above size range, European workers usually possess seta counts of 20 or more; Asiatic workers often range below this and in some cases may be distinguishable only by comparing intranidal trends with the regression zones . . . . . Lasius niger
Head of Lasius niger worker
Profile of Lasius niger worker

6

return to couplet #1

  • Worker body color jet black; the scutum of the queen seen in perfect side view overhangs the pronotum and claims the entire anterior thoracic convexity . . . . . 7
  • Worker body color yellow to yellowish brown; the scutum of the queen does not overhang the pronotum but shares with it the anterior thoracic convexity . . . . . 9

7

return to couplet #6

  • Antennal scapes of the worker flattened to the extent that for most of their length the minimum measureable width at any point is less than half the maximum measurable width at that point; the queen is an extreme “beta” form, with greatly flattened scapes, femora, tibiae, and metatarsi (Japan and Korea) . . . . . Lasius spathepus
  • Antennal scapes of the worker short-elliptical in cross-section, so that for most of their length the minimum width at any point is 0.8 X the maximum width at that point or more; the queen is an “alpha” form, with normal appendages, the scape short-elliptical in cross-section . . . . . 8

8

return to couplet #7

  • Queen with many body and appendage hairs curved at the tip or sinuate, those on the appendages often curving back to touch the cuticular surface again; body pubescence sparse or absent, the cuticular surface smooth and shining; worker (tentatively associated) with the standing hairs of the second and third gastric tergites (exclusive of the extreme posterior strips) reaching a maximum length of 0.10-0.12 mm, and as long as the standing hairs on the pronotum or longer; in side view the petiolar crest thin and sharp (Japan and Korea) . . . . . Lasius crispus
  • Queen with few or no hairs curved at the tip or sinuate; body covered with abundant appressed pubescence which at least partly obscures the shining cuticular surface; worker with the standing hairs of the second and third gastric segments (exclusive of the extreme posterior strips) never as long as 0.10 mm, and rarely exceeding 0.08 mm., usually shorter than the standing hairs of the pronotum; the petiolar crest in side view thicker and blunter (England to Japan) . . . . . Lasius fuliginosus
Lasius fuliginosus casent0173166 profile 1.jpg

9

return to couplet #6

  • Dorsal crest of the worker petiole seen in frontal view strongly convex and never emarginate . . . . . 10
  • Dorsal crest of the worker petiole at the most feebly convex and often emarginate . . . . . 11

10

return to couplet #9

  • Eyes of worker set in shallow but distinct circumocular depressions; pilosity of first gastric tergite predominantly decumbent; PW not exceeding 0.63 mm.; queen exceedingly small, HW 0.76-0.78 mm . . . . . Lasius carniolicus
Head of Lasius carniolicus worker
Profile of Lasius carniolicus worker
  • Eyes of worker not set in depressions; pilosity of first gastric tergite predominantly subdecumbent-erect; PW of three workers measured 0.88-0.93 mm.; queen exceptionally large, HW of single specimen measured 1.99 mm. (known only from the Himalayas) . . . . . Lasius crinitus
Lasius crinitus casent0903213 p 1 high.jpg

11

return to couplet #9

  • Worker eyes with less than 30 ommatidia (if the nest series splits on this couplet, go to 12) . . . . . 12

12

return to couplet #11

  • Scapes and tibiae of worker with numerous standing hairs prominent above the ground pubescence (eastern Asia) . . . . . Lasius talpa
Lasius talpa casent0903665 p 1 high.jpg
  • Worker scapes and tibiae with few or no standing hairs (England to Japan) . . . . . Lasius flavus (in part - also #15)
Lasius flavus casent0005406 profile 1.jpg

13

return to couplet #11

  • In both the worker and queen, the dorsal border of the petiole in frontal view narrow and deeply emarginate, the depth of the emargination measured from the level of the bicornuate dorsal crest to the bottom of the emargination at least as great as the width of the emargination measured at the level of the middle of the depth measurement . . . . . Lasius bicornis
Head of Lasius bicornis worker
Profile of Lasius bicornis worker
  • Dorsal border of the petiole with never more than a right-angular emargination . . . . . 14

14

return to couplet #13

  • Either the genal margins of the worker seen in full face with standing hairs prominent above the ground pubescence; or else the longest hairs of the posterior half of the first gastric tergite (exclusive of: the extreme posterior strip) are distinctly less than half as long as the maximum width of the hind tibia at its midlength. In the queen the head width is about the same as the width of the thorax just anterior to the teguJae or greater . . . . . Lasius umbratus or . . . . . Lasius rabaudi (see key to queens).
Lasius umbratus casent0005409 profile 1.jpg
  • Genal margins of worker seen in full face lacking standing hairs; the longest hairs of the posterior half of the first gastric tergite (exclusive of the extreme posterior strip) at least half as long as the maximum width of the hind tibia at its midlength. In the queen the head width is much less than the width of the thorax just anterior to the regulae . . . . . 15

15

return to couplet #14

  • (A species known from only one nest series from the Himalayas.) Terminal maxillary palp segment of worker slightly longer than the penultimate segment; the segments as a whole longer (see under diagnosis of this species) . . . . . Lasius alienoflavus
Head of Lasius alienoflavus worker
Profile of Lasius alienoflavus worker
  • (A widespread and abundant Holarctic species.) Terminal maxillary palp segment of worker at most as long as the penultimate . . . . . Lasius flavus (in part - also #12)
Lasius flavus casent0005406 profile 1.jpg