Key to Lasius Nearctic workers with long maxillary palpi

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.

Some notes about this key: This key does not include the species once believed to be a separate genus, Acanthomyops. Links to keys for Nearctic Acanthomyops workers, queens and males can be found on the Lasius genus page.

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Lasius

1

 * Eye large, at least 10 ommatidia (usually more than 12) in maximum diameter; maximum eye length 0.20 X the head width or more . . . . . 2
 * Eye small, less than 12 ommatidia in maximum diameter; maximum eye length 0.17 X the head width or less . . . . . 7

2
return to couplet #1
 * In a given nest series all larger workers (PW 0.57 mm. or more) and most smaller workers with one or more offset teeth at the basal angle of the mandible; male mandible with a narrow preapical cleft setting off a narrow, acute apical tooth, and with a well defined basal angle . . . . . Lasius pallitarsis


 * Workers of all sizes with the posterior basal tooth aligned with the adjacent teeth of the masticatory border; male mandible lacking a narrow preapieal cleft and well-defined basal angle, the masticatory border curving gradually into the basal border . . . . . 3

3
return to couplet #2
 * Maximum eye length usually less than 0.25 X the head width and never more; color always yellowish brown; scapes always lacking standing hairs (southwestern U. S. and Mexico) . . . . . Lasius sitiens


 * Maximum eye length exceeding 0.25 X the head width, even if only slightly; color occasionally yellowish brown, but then the scapes have standing hairs . . . . . 4

4
return to couplet #3
 * In one or both mandibles of a majority of the nest series, either the penultimate basal tooth is markedly reduced in size relative to the two flanking teeth, or the gap between the penultimate and terminal basal teeth tends to be larger in area than the terminal basal tooth and variable in shape; when viewed with the mandibles opened and the head held in perfect full face (at maximum head length and with the occipital and anterior clypeal borders horizontally aligned), the anterior border of the median clypeal lobe is angulate, i.e, formed of two straight sides meeting at the midline to form an obtuse, usually pointed angle . . . . . 5
 * In all of the workers of a nest series, with rare exceptions, the penultimate and terminal basal teeth are subequal in size, and the gap between them has about the same area as the terminal tooth and is constant in shape; when viewed with the mandibles opened and the head held in perfect full face, the anterior border of the median clypeal lobe describes an even, broad parabolic curve, with the sides at least feebly convex and only occasionally meeting in a point at the midline . . . . . 6

5
return to couplet #4
 * The scapes and tibiae of all workers except nanitics (PW less than 0.40 mm.) bearing standing hairs; body color light brown to medium brown, very rarely dark brown . . . . . Lasius neoniger


 * The scapes and tibiae lacking standing hairs and usually without hairs of any inclination (but pubescence still abundant); color typically dark brown . . . . . Lasius crypticus

6
return to couplet #4
 * Within the size range PW 0.53-0.70 mm., scapes and tibiae bearing few or no standing hairs, the seta count always less than 20 and usually less than 10 . . . . . Lasius americanus


 * Within the above size range, the scapes and tibiae bearing numerous standing hairs, the seta count usually greater than 10 (western U. S. only) . . . . . Lasius niger  Schar et al. 2017 - The natural North American populations identified as Lasius niger are not conspecific and belong to a currently undescribed species.

7
return to couplet #1
 * Dorsal crest of the worker petiole seen in frontal view strongly convex and non-emarginate . . . . . Lasius humilis


 * Dorsal crest of the worker petiole at most feebly convex and often emarginate . . . . . 8

8
return to couplet #7
 * Eyes with less than 35 ommatidia . . . . . 9
 * Eyes with 35 or more ommatidia . . . . . 11

9
return to couplet #8
 * Outer surfaces of each tibia with numerous standing hairs prominent above the ground pubescence (western U. S.) . . . . . Lasius fallax


 * Outer surfaces of each tibia with at most one or two standing hairs . . . . . 10

10
return to couplet #9
 * Terminal segment of the maxillary palp longer than the penultimate segment in at least a majority of the workers of the nest series (eastern North America to Wyoming) . . . . . Lasius nearcticus


 * Terminal segment of the maxillary palp in all of the workers of the nest series at most as long as the penultimate segment (Nova Scotia to California) . . . . . Lasius brevicornis

11
return to couplet #8
 * At least a broad longitudinal median strip of the second gastric tergite, exclusive of the extreme posterior portion, almost completely devoid of pubescence of any kind and with only a few widely scattered standing hairs, its cuticular surface extremely smooth and shining at low magnifications (eastern U. S.) . . . . . Lasius speculiventris


 * Central area of second gastric tergite covered by abundant pubescence and standing hairs, its surface feebly shining to subopaque at low magnifications . . . . . 12

12
return to couplet #11
 * Longest hairs of the posterior half of the first gastric tergite, exclusive of the extreme posterior strip, not exceeding in length 0.50 X the maximum width of the hind tibia at its midlength . . . . . Lasius umbratus


 * Longest hairs of the posterior half of the first gastric tergite, exclusive of the extreme posterior strip, at least 0.60 X as long as the maximum width of the hind tibia at its midlength . . . . . 13

13
return to couplet #12
 * Worker: body color brownish yellow; lateral tibial surfaces completely lacking standing hairs; longest hairs of the posterior half of the first gastric tergite, exclusive of the extreme posterior strip, often as long as the maximum width of the hind tibia at midlength or longer; pubescence of gastric tergites dense, often lending a greyish overcast to the cuticle under low magnifications; queen small, HW 1.02-1.17 mm. (eastern North America) . . . . . Lasius minutus


 * Worker: body color clear yellow; lateral tibial surfaces often with standing hairs; longest hairs of the posterior half of the first gastric tergite, exclusive of the extreme posterior strip, never exceeding 0.80 X the maximum width of the hind tibia at midlength; pubescence of gastric tergites lighter, rarely dense enough to lend a greyish overcast to the cuticle; queen larger, HW never less than 1.30 mm . . . . . 14

14
return to couplet #13
 * Pilosity of posterior half of first gastric tergite, exclusive of the extreme posterior strip, at least in part decumbent-subdecumbent; standing hairs sparse or absent on the lateral tibial surfaces (maritime Canada to Arizona) . . . . . Lasius subumbratus


 * Pilosity of posterior half of first gastric tergite, exclusive of the extreme posterior strip, almost entirely suberect-erect; standing hairs often abundant on the lateral tibial surfaces (Pacific Coast to Idaho) . . . . . Lasius vestitus