Key to Lasius-Nearctic Acanthomyops males

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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 other two, as relatively few of the nest samples studied contained males. Consequently the limits of variation of the diagnostic characters of this caste are poorly known. An attempt to circumvent the consequences of ignorance was made by running several species out twice. A serious study of males, including comparative data on genitalia, might result in a fairly reliable key. The work of Clausen (1938) strongly suggests that the subgenital plate may be the best single structure for separating the males of Lasius. Unfortunately he did not clearly indicate the degree of variability of this structure. Wilson (1955) found that the subgenital plate was fairly variable in some species of Lasius. The usefulness of the subgenital plate as a diagnostic character in Acanthomyops should be investigated.

There are 14 species included in the key; the male of pubescens is unknown. The male specimens included in a sample of pogonogynus are murphyi. The males included in samples of the taxon known as alpha-latipes are latipes. No males were associated with samples of the other 3 hybrid taxa.

Fortunately the male key will not be used much, since samples containing only males are not often sent in for identification or collected by entomologists. The reliability of this key is difficult to state, but may approach the 85 to 90 percent level, especially if series of specimens are available in the more variable species.

1

  • At least a few standing hairs on dorsum of alitrunk distally plumose, others simple or barbulate . . . . . Lasius plumopilosus
  • No standing hairs distally plumose anywhere on body, all simple or barbulate . . . . . 2

2

return to couplet #1

  • Crest of petiolar scale moderately to very blunt as viewed from the side . . . . . 3
  • Crest of petiolar scale moderately to very sharp as viewed from the side . . . . . 5

3

return to couplet #2

  • As seen from the side, 20 or more standing hairs cover entire gula. Body and appendages quite hairy, fore femur with 20 or more standing hairs with maximum length of nearly 0.10 mm. Antennal scapes stout, thickened towards apex, and covered with prominent suberect pubescence. Apex of parameres usually distinctly truncate. AL usually 1.70 mm or more . . . . . Lasius latipes
  • As seen from the side, fewer than 20 standing hairs usually covering posterior ¥3 of gula, or centrally located. Body and appendages at most moderately hairy, on fore femur, usually 12 or fewer standing hairs with maximum length usually well under 0.10 mm. Antennal scapes slender, at most only very slightly thickened distally, usually covered with appressed to decumbent pubescence. Apex of parameres usually rounded. AL varying, usually 1.60 mm or less . . . . . 4

4

return to couplet #3

  • In side view, crest of petiolar scale only moderately blunt; in anterior view, crest straight to slightly emarginate, sides more or less straight and usually converging dorsally. Located centrally on gula, 2 to 4 standing hairs ranging from 0.10 to 0.15 mm in length. Fore femur with 2 or 3 short standing hairs, 0.04 mm or less in length, middle and hind femora usually without standing hairs. Clypeus with 10 to 12 standing hairs, usually all straight . . . . . Lasius californicus
  • In side view, crest of petiolar scale very blunt; in anterior view, crest and sides convex. Usually located on posterior 2/3 of gula, 6 or more standing hairs less than 0.10 mm long. Each femur with 10 to 12 standing hairs, usually 0.06 mm or more in length. Clypeus with 16 or more standing hairs, some flexed and twisted . . . . . Lasius murphyi

5

return to couplet #1

  • Longer hairs at posterior tip of gaster 0.27 mm or more. Gula without or with standing hairs, longest measuring 0.18 to 0.20 mm or more . . . . . 6
  • Longer hairs at posterior tip of gaster less than 0.27 mm. Gula usually with standing hairs, the longest usually measuring well under 0.18 mm . . . . . 9

6

return to couplet #5

  • Gula without standing hairs, those on rest of body sparse. Pubescence very dilute over entire body. AL 1.45 mm or less . . . . . Lasius arizonicus
  • Gula with at least a few standing hairs, those on rest of body fairly numerous. Body pubescence and size varying . . . . . 7

7

return to couplet #6

8

return to couplet #7

  • Standing hairs on fore femur numbering 0 to 2. Pubescence on gaster very dilute, on most of head moderately dense. SI usually 70 or more . . . . . Lasius interjectus
  • Standing hairs on fore femur numbering 4 or more. Pubescence on gaster dilute to moderately dense, on most of head dilute. SI usually 68 or less . . . . . Lasius claviger

9

return to couplet #5

  • Longer hairs at tip of gaster less than 0.20 mm, and often less than 0.15 mm . . . . . 10

10

return to couplet #9

  • A larger species, AL ranging from 1.35 to 1.60 mm. In anterior view, crest of petiolar scale slightly convex to straight, occasionally with a faint emargination. Standing body hairs delicate. Body color usually dark brown . . . . . Lasius subglaber
  • A smaller species, AL ranging from 1.05 to 1.30 mm. In anterior view, crest of petiolar scale usually distinctly emarginate, in a few cases only slightly emarginate; less commonly straight. Standing body hairs normal to moderately coarse. Body color usually light brown . . . . . Lasius occidentalis

11

return to couplet #9

  • Mesoscutum with at least central area free of pubescence . . . . . 14

12

return to couplet #11

  • Both mesoscutum and mesoscutellum completely covered with long pubescence hairs 0.10 mm or more in length . . . . . Lasius mexicanus
  • At least central area of mesoscutellum free of pubescence hairs, all of which are shorter, falling well under 0.10 mm . . . . . 13

13

return to couplet #12

  • Pubescence on gaster dense. In side view, petiolar scale sharp at crest, very broad at base, and with sides straight; approximating an equilateral triangle. Body color dark castaneous brown . . . . . Lasius bureni
  • Pubescence on gaster dilute. In side view, petiolar scale moderate at crest, only moderately broad at base and with front side irregular; not triangular. Body color light to medium brown . . . . . Lasius californicus

14

return to couplet #11

  • HW 0.85 mm or less. Standing and pubescence hairs quite delicate. Body color light brown . . . . . Lasius creightoni
  • HW 0.90 mm or more. Hairs not especially delicate. Body color medium brown to dark brown . . . . . 15

15

return to couplet #14

  • Standing hairs on fore femur 0 to 2. Pubescence on most of front of head moderately dense. SL usually 0. 70 mm or more, SI 70 or more . . . . . Lasius interjectus
  • Standing hairs on fore femur 4 or more. Pubescence on most of front of head dilute to very dilute. SL usually 0.69 mm or less, SI 68 or less . . . . . 16

16

return to couplet #15

  • Pubescence on sides of second tergite of gaster dilute to very dilute, pubescence hairs usually at least twice as far apart as long. Width of scale at level of petiolar spiracle usually not over 1.3 times height of scale above spiracle. Terminal width of pygostyles 0.03 mm or less. A smaller species, usually HW 0.99 mm or less and SL 0.63 mm or less. Body color dark to very dark brown, often appearing black or nearly black to the naked eye . . . . . Lasius coloradensis
  • Pubescence on sides of second tergite of gaster dilute to moderately dense, hairs rarely farther apart than long. Width of scale at level of petiolar spiracle usually at least 1.5 times height of scale above spiracle. Terminal width of pygostyles 0.04 mm or more. A larger species, usually HW 1.00 mm or more and SL 0.64 mm or more. Body color medium to moderately dark brown, but rarely dark enough to appear black or nearly black to naked eye . . . . . Lasius claviger