Key to Lasius-Nearctic Acanthomyops workers

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This worker key is based on: Wing, M. W. 1968. Taxonomic revision of the Nearctic genus Acanthomyops (Hymenoptera: Formicidae). Cornell University, New York State College of Agriculture, Agricultural Experiment Station, Ithaca, NY, Memoir No. 405. 173 pages.

Wing 1968 Acanthomyops

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Wing's preface: This key is less reliable than the queen key, but more reliable than the male key. A large number of specimens was available for study, but only minor differences of structure, pilosity, size, and color exist between the workers of many taxa. The closeness of some of the species in conventional taxonomic characters is often paralleled in metric characters. This made it difficult to construct a key that was both workable and comprehensible.

An attempt has been made to use as many relatively stable characters as possible in constructing the key. It is especially important that the various statements of a couplet be treated as a group in the worker key. Some of the characters used are not concordant, others are to a degree, but often are rather weak in their positive correlation. This makes it possible to use what amounts to a “majority vote” in deciding which route to take in the key. Extensive use of illustrations, frequency tables, and regression figures should supplement the worker key.

The number of outcomes in the key is 18. This includes 15 species, an atypical form of claviger, and 5 hybrid taxa, 3 of which are lumped with latipes. In general this key should enable the user to correctly identify at least 95 percent of his specimens, provided that a series of workers is available.

1

  • All standing body hairs simple, or weakly to strongly barbulate; never plumose distally . . . . . 2

2

return to couplet #1

  • Gula without standing hairs, or rarely with, at most 1 or 2, which are much shorter than those on clypeus. Standing hairs on dorsum of gaster measuring 0.20 to 0.25 mm, almost invariably confined to posterior edges of tergites beyond first. Pubescence on gula and gaster extremely dilute . . . . . Lasius arizonicus
  • Gula usually with standing hairs, length and distribution of those on gaster varying; in the few cases where hairs are absent on gula, then standing hairs on dorsum of gaster are not confined to posterior edges of tergites beyond first, and/or pubescence on gula and gaster is from moderate to very dense . . . . . 3

3

return to couplet #2

  • Length of longer standing hairs on dorsum of gaster 0.23 mm or more, on gula usually 0.20 mm or more. In side view, crest of petiolar scale sharp to moderately sharp; in anterior view, usually emarginate. Standing hairs on dorsum of gaster either strictly confined to posterior edges of tergites beyond first, or, if more or less widely distributed, then concentrated toward caudal margins . . . . . 4
  • Standing hairs on dorsum of gaster rarely more than 0.22 mm long, but if so, those on gula are less than 0.20 mm. Crest of petiolar scale varying as to sharpness and emargination. Standing hairs on dorsum of gaster varying, but usually more or less uniformly distributed over its surface, unless petiolar scale is moderate to blunt in side view, then there may be a relatively greater number of hairs on the caudal margins of tergites . . . . . 5

4

return to couplet #3

  • HW 1.08 mm or greater, CI at least 98, usually 100 or more, SI usually 85 or less, and AL usually 1.40 mm or greater. Standing hairs on dorsum of gaster almost invariably confined to posterior edges of tergites beyond first, which has basal hairs. Pubescence on head moderate to dense. Mandible with 1 or more denticles on its basal margin . . . . . Lasius interjectus
  • HW 1.02 mm or less, CI usually 96 or less, SI 86 or more, and AL 1.30 mm or less. Standing hairs on dorsum of gaster more irregularly distributed over surface, but with majority of hairs on posterior edges of tergites beyond first. Pubescence on head dilute to very dilute. Mandible rarely with a denticle on its basal margin . . . . . Lasius colei

5

return to couplet #3

  • In side view, crest of erect petiolar- scale well below level of propodeal spiracle, blunt; in anterior view, with a standing hair on each corner. Gaster very densely pubescent, body color brownish yellow. SI 83 or more . . . . . Lasius pubescens
  • In side view, crest of erect petiolar scale either at or above level of propodeai spiracle, or not blunt; or, in anterior view, with at least a row of hairs. Pubescence on gaster, body color, and SI varying . . . . . 6

6

return to couplet #5

  • In side view, crest of petiolar scale very to moderately blunt; in anterior view, convex, straight, or in rare cases with a slight median emargination. Standing hairs on gula almost always distributed over entire surface as viewed from the side . . . . . 7
  • In side view, crest of petiolar scale moderately to very sharp; in anterior view, usually broadly emarginate. In a few cases crest may be straight or, more rarely, slightly convex. Standing hairs on gula almost always covering only the posterior ¾ or ½ of its surface, but in a few specimens, especially claviger from in or near North Carolina and Virginia, the entire gula may be covered with standing hairs . . . . . 9

7

return to couplet #6

  • Standing hairs noticeably more numerous on propodeum than elsewhere on dorsum of alitrunk. Lateral surface and flexor edge of fore femur usually with 10 or fewer standing hairs, 0.05 mm or less in length. Length of standing hairs on gula, propodeum, and dorsum of gaster usually 0.10 mm or less. Antennal scapes with appressed pubescence . . . . . Lasius murphyi
  • Standing hairs more or less evenly distributed over dorsum of alitrunk. Other characters varying . . . . . 8

8

return to couplet #7

  • Number of standing hairs on gula 20 or more, often as many as 40, usually 0.12 mm or more in length. Lateral surface and flexor edge of fore femur usually with 12 or more standing hairs 0.06 mm or more in length. Longer standing hairs on dorsum of gaster 0.13 mm or more. Pubescence on antennal scapes varying from fully appressed to strongly suberect . . . . . Lasius latipes ( = beta-latipes of authors)

NOTE: This couplet also receives 2 latipes hybrids: pogonogynus (Buren) and alpha-latipes of authors, and presumably the hybrid taxon latipes X coloradensis. An occasional aberrant specimen of claviger (eastern U.S.) or coloradensis (western U.S.) may fall here. See text under the appropriate species or hybrid for further details on the separation of these taxa.

  • Number of standing hairs on gula 16 or fewer, not more than 0.10 mm long. Lateral surface and flexor edge of fore femur with 10 or fewer standing hairs, usually not more than 0.06 mm long. Longer standing hairs on dorsum of gaster usually 0.12 mm or less. Pubescence on antennal scapes decumbent to strongly suberect . . . . . Lasius murphyi X subglaber hybrid

9

return to couplet #6

  • Standing body hairs either simple and delicate, or strongly barbulate. Standing hairs on fore femur varying, but if hairs delicate, then usually 5 or less, often only 2 or 3, and usually 0.05 mm or less in length, often only 0.03 or 0.04 mm. Longer standing hairs on gula usually less than 0.10 mm. In side view, crest of petiolar scale moderate; in anterior view, slightly convex, straight or shallowly emarginate. Pubescence on antennal scapes almost always suberect. SI 78 or less . . . . . 10
  • No standing body hairs strongly barbulate or unusually delicate, all simple or weakly barbulate. Standing hairs on fore femur somewhat variable, but usually either 6 or more, often as many as 15; or 0.06 mm or longer, often as long as 0.20 mm, or both. Longer standing hairs on gula usually 0.10 mm or more in length. In side view, crest of petiolar scale very to moderately sharp; in anterior view, usually emarginate, often deeply so. Pubescence on antennal scapes and SI varying . . . . . 11

10

return to couplet #9

  • Many standing body hairs strongly barbulate and coarse . . . . . Lasius subglaber X plumopilosus hybrid

11

return to couplet #9

  • In side view, clypeus with a peculiar, deep indentation below the middle; otherwise characters agree reasonably well with a small worker of claviger. Sample 5. . . . . . Lasius claviger (in part - also #18)

12

return to couplet #11

  • Pubescence on sides of second tergite of gaster dense to very dense, distance between bases of pubescence hairs usually averaging well below 1/3 of their length, often contiguous. Most of body and appendages quite densely pubescent . . . . . 13
  • Pubescence on sides of second tergite of gaster dilute to moderate, distance between bases of pubescence hairs usually averaging more than 'h of their length, often several times their length. Rest of body and appendages somewhat variable, but usually never more than moderately pubescent . . . . . 14

13

return to couplet #12

  • In anterior view, crest of petiolar scale usually with a distinct median emargination; sides more or less straight. Longer standing hairs on gula usually less than 0.12 mm. As seen in perfect full-face view, 18 or more standing hairs on occiput, the border of which is medially emarginate in many specimens. Body and appendages yellow to brownish yellow . . . . . Lasius occidentalis
  • In anterior view, crest of petiolar scale straight or shallowly emarginate; sides convex. Longer standing hairs on gula usually 0.12 mm or more in length. As seen in perfect full-face view, 16 or fewer standing hairs on occiput, the border of which is straight. Body and appendages yellowish brown to brown . . . . . Lasius bureni

14

return to couplet #12

  • Essentially all pubescence on antennal scapes conspicuously suberect. Pubescence hairs on gula and fore femur mostly suberect . . . . . 15
  • Pubescence hairs on antennal scapes either all appressed, a few decumbent to suberect, or many hairs decumbent. Pubescence on gula and fore femur appressed or decumbent . . . . . 16

15

return to couplet #14

  • Length of standing hairs on gula 0.13 mm or more, on dorsum of gaster 0.18 mm or more. Pubescence delicate. Color yellow . . . . . Lasius creightoni.
  • Length of standing hairs on gula usually 0.12 mm or less, on gaster usually 0.17 mm or less. Pubescence coarser. Color yellowish brown to brown . . . . . Lasius coloradensis (in part - also #18)

16

return to couplet #14

  • Length of longer standing hairs on the following structures usually not over the stated amounts: clypeus, 0.11 mm; occiput, 0.10 mm; fore femur 0.06 mm; and dorsum of propodeum, 0.12 mm. Propodeum usually convex in profile. In side view, crest of erect petiolar scale above to well above level of propodeal spiracle . . . . . Lasius mexicanus
  • Length of longer standing hairs on clypeus, occiput, fore femur, and propodeum usually exceeds amounts stated above, often by nearly 100 percent. Propodeum rarely convex in profile. In side view, height of erect petiolar scale with respect to propodeal spiracle varying, but crest often at or below level of propodeal spiracle . . . . . 17

17

return to couplet #16

  • Standing hairs on fore femur usually numbering 6 or fewer; on hind femur, none. Longer hairs on crest of petiolar scale usually 0.13 mm or more. A few standing hairs on dorsum of alitrunk moderately to strongly flexed. In many specimens standing hairs few or lacking in a central area of varying size on dorsum of gaster. Mandible sometimes with a denticle on its basal margin. SI 81 or more . . . . . Lasius californicus
  • Standing hairs on fore femur usually numbering 7 or more, on hind femur, 0 to 5. Longer hairs on crest of petiolar scale usually 0.12 mm or less. Standing hairs on alitrunk usually all more or less straight, those on dorsum of gaster more or less evenly distributed over its surface. Mandible without a denticle on its basal margin. SI 80 or less for most specimens . . . . . 18

18

return to couplet #17

  • Most specimens falling above the critical dividing line, SL = 1.27 (HW) - 0.505. (A few small specimens of claviger, including its synonym parvulus, fall here). New Mexico to Manitoba and west. See text for further discussion . . . . . Lasius coloradensis (in part - also #15)
  • Most specimens falling on or below the critical dividing line, SL = 1.27(HW) - 0.505. Kansas to Minnesota and east. See text for further discussion . . . . . Lasius claviger (in part - also #11)
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