Sociobiology 35(2), in press (2000)

A Review of the New World ants of the subgenus Myrafant, genus Leptothorax (Hymenoptera: Formicidae)

William Mackay
(submitted 11 September, 1999)

This manuscript is in press in Sociobiology, and will appear in early 2000. It is being made available at this time to allow for the identification of specimens only. Please do not use any of the unpublished information in this paper, or use any of the names of the new species, as that would invalidate them. The figures were removed to conserve space. I will try to make the entire manuscript available as a pdf file on this website, a Word file is available if you send me a zip disk.
- The manuscript names in this paper are part of a conditional proposal (sensu Article 15 of the 1985 ICZN), and thus not made available here. Their appearance here or in any duplication of this manuscript does not constitute publication (sensu Article 8 of the 1985 ICZN).

The complete paper will soon be available in pdf format on this site. An html-version is currently being prepared. To facilitate identification, a series of keys to the species will be made available as soon as possible.


Key to the Species of Leptothorax subgenus Myrafant in the New World, based primarily on workers

  1. Petiole and postpetiole armed with spine-like protuberances (Fig. 1) ............ Subgenus Nesomyrmex (see Kempf, 1959 for key to species)
    - Petiole and postpetiole without spine-like protuberances (Fig. 2) ............
    2
  2. (1). Petiole with elongate peduncle (Fig. 2); mesosoma either strongly arched (Fig. 2) or mesopropodeal suture deeply impressed (Fig. 3) ............3
    - Petiole without elongate peduncle (Fig. 4), or dorsum of promesonotum flat (Fig. 9) or feebly convex in profile; meso-propodeal suture at most feebly impressed (except for L. hispidus, see Fig. 5) ............ 4
  3. (2). Dorsum of mesosoma strongly arched (Fig. 2) ............ Sub-genus Macromischa (see Baroni Urbani, 1978 for key to species)
    - Dorsum of promesonotum not strongly convex in profile (Fig. 3); mesopropodeal suture deeply impressed (Fig. 3) ............ Subgenus Dichothorax, L. pergandei (see Mackay, 1993a)
  4. (2). Clypeus without carinae on medial surface (Fig. 6), but usually with carinae present anterior to frontal carinae, middle of clypeus usually concave with longitudinal depression (Fig. 6); antennal scapes often with erect or suberect hairs (Fig. 7) ............ Subgenus Leptothorax (see Creighton, 1950: 257-258 for key to species) and genus Formicoxenus (see Francoeur and Loiselle, 1985 for assistance with species identifications).
    - Clypeus with medial, longitudinal carina (Fig. 8), in addition to several lateral carinae; scape usually without erect hairs ............ 5 (Subgenus Myrafant)
  5. (4). Posterior corner of propodeum completely rounded, with-out evidence of angles or spines (Fig. 9); México ............ striatulus Stitz
    - Posterior corner of propodeum with angles or spines (Fig. 10); widely distributed in North America, including México ............
    6
  6. (5). Antennae with 12 segments (Fig. 11, left) (usually easier to count with funiculus held at an oblique angle) ............7
    - Antennae with 11 segments (Fig. 11, right) ............ 49
  7. (6). Disc (at least basal 1/3) of first tergum of gaster predominantly reticulo - punctate (Fig. 12, left), (sculpture may be very weak and difficult to see); Nevada to Colorado, Arizona to west Texas south to northern México ............ 8
    - Entire disc (except possibly region immediately poster-ior to connection of postpetiole) of first tergum of gaster completely smooth, polished and shining (Fig. 12, right); widely distributed in North America (including México and Guatemala) ............ 12
  8. (7). Propodeal angles dentiform or bump-like (Fig. 13); mesosomal outline varies, often impressed (Fig. 5) ............ 9
    - Propodeal spines well formed (Fig. 10), often half as long as, or even longer than, the distance between their bases (Fig. 17); mesosoma not impressed at the mesopropodeal suture (Fig. 14) ............ 10
  9. (8). Mesosoma somewhat impressed at mesopropodeal suture (Fig. 5); head mostly rugose with few punctures ............ hispidus Cole
    - Mesosoma not depressed at mesopropodeal suture (Fig. 14); head heavily and densely punctate ............
    andersoni new species
  10. (8). Eye oval in shape (Fig. 16, left); dorsum of mesosoma with coarse, longitudinal rugae; shape of petiolar node varies; hind femur greatly thickened (Fig. 15); Arizona and Nuevo León ............ 11
    - Eye elongate, kidney shaped (Fig. 16, right); dorsum of mesosoma finely punctate with no evidence of rugae; petiolar node in profile with relatively sharp apex (Fig. 18); hind femora not greatly thickened; NV, CO, NM, TX ............ obliquicanthus Cole
  11. (10). Petiolar node in profile nearly as broad apically as basally (Fig. 17); propodeal spines nearly as long as distance between them; Arizona ............ silvestrii (Santschi)
    - Petiolar node with sharp apex (Fig. 18); propodeal spines short, less than 1/2 distance between bases; México (Nuevo León) ............ rugosus new species
  12. (7). Dorsum of mesosoma very smooth and shiny (Fig. 19, left), entirely devoid of sculpture except for small and widely spaced piligerous punctures ............ 13
    - Dorsum of mesosoma sculptured (Fig. 19, right), or at least never entirely smooth and shining, if mostly smooth and shining, at least dorsum of propodeum sculptured ............ 14
  13. (12). Propodeal spines long (Fig. 20), (longer than broader at their bases); Colorado ............ schmittii Wheeler
    - Propodeal spines short (Fig. 21) (shorter than distance between bases); widely distributed in western North America ............nitens Emery
  14. (12). Eyes tiny (Fig. 22, left), maximum length about 1/2 distance between base of mandible and anterior edge of eye; California ............ ocellatus new species
    - Eyes larger (Fig. 22, right), maximum diameter ranging from 1/2 length between base of mandible and anterior edge of eye, to about as long as this distance; widely distributed ............
    15
  15. (14). Dorsum of head at least in part smooth and shining (Fig. 22, left); if head is partly sculptured, at least central area smooth and shining and petiolar node is angulate in profile, with relatively sharp apex (Fig. 18) ............ 16
    - Head largely or entirely sculptured (Fig. 22, right), surface feebly shining only between sculpture, or completely opaque; if head is partially smooth and shining, then petiolar node is rounded and blunt or 17
  16. (15). Dorsum of head entirely smooth and polished (Fig. 25), striae or rugae present on sides of head (Fig. 25); southern Texas, México and Guatemala .……………………………............… 17
    - Dorsum of head partially to mostly smooth and shining (Fig. 22, left), area adjacent to broad, central, shining strip with sculpture, often very fine; widely distributed in USA and México ............ 21
  17. (16). Propodeal spines well developed (Fig. 23), nearly half as long as distance between bases; semicircular striae posterior to insertions of antennae present (Fig. 22 right) or absent (Fig 25, left) ............ 18
    - Propodeal armature consisting of only small angles or tiny spines (Fig. 24); semicircular striae present posterior to insertions of antennae (Fig. 25, right) ............ 19
  18. (17). Semicircular striae absent posterior to insertion of antennae (Fig. 25, left) ............ stollii Forel
    - Semicircular striae present posterior to insertion of antennae (Fig. 25, right) ............ bicolor new species
  19. (17). Hairs on scape decumbent (Fig. 26, left, middle); hairs on dorsum of head very fine and dispersed; widely distributed in Texas and México ............ 20
    - Hairs on scape suberect to nearly erect (Fig. 26 right); hairs on dorsum of head coarse and abundant; Michoacán ............ brevispinosus new species
  20. (19). Mesopleuron and sides of propodeum with rugae (Fig. 27); side of pronotum predominantly smooth and glossy; Hidalgo, Morelos and Nuevo León ............ manni Wheeler
    - Mesopleuron and sides of propodeum punctate (Fig. 28); side of pronotum with fine striae; western Texas and Coahuila ............ bristoli new species
  21. (16). Petiolar node blunt in profile (Fig. 27); nearly entire head smooth and shining (Fig. 25, left), area adjacent to polished central strip with very fine sculpture ............ 22
    - Petiolar node in profile with angulate apex (Fig. 29); entire dorsum of head often smooth and shining, at least posterior half of head in part smooth and shining, with broad, central strip which is free of sculpture (Fig. 25, right), extending posteriorly to vertex ............ 24
  22. (21). Entire dorsum of head with fine striae (Fig. 30, left); dorsal surface of postpetiole smooth and shining; nests under stones ............ mexicanus new species
    - Central region of dorsum of head mostly free of sculpture (Fig. 30, right), region adjacent to central strip with fine punctures or costulae; dorsal surface of postpetiole densely punc-tate (Fig. 33, left) ............
    23
  23. (22). Eyes small, distance from insertion of mandible to anterior border of eye about 1.2 X maximum diameter of eye (Fig. 30, right); New Mexico and southern Texas ............ cokendolpheri new species
    - Eyes larger, distance from insertion of mandible to anterior border of eye about equal to maximum eye diameter (Fig. 31, left); central México (state of México) ............ punctithorax new species
  24. (21). Much of the dorsum of head smooth and shining (Fig. 30, right); petiolar node in profile with very sharp apex (Fig. 29) ............ 25
    - Head usually with only a central strip free of sculpture (Fig. 31, right); petiolar node in profile with a relatively sharp apex (Fig. 32) ............ 26
  25. (24). Posterior surface of petiolar node with punctures (Fig. 33, left); New Mexico ............ melinus new species
    - Posterior surface of petiolar node with fine rugulae (Fig. 33, right); Oregon, California and Arizona ............ mariposa Wheeler
  26. (24). Dorsum of pronotum mostly glossy with a few longitudinal fine striae, but with little or no evidence of punctures (Fig. 34, left); region between propodeal spines finely punctate, nearly smooth ............ nitens Emery
    - Dorsum of pronotum punctate with little evidence of striae (Fig. 34 right); region between spines sculptured with fine rugae, or punctate ............
    27
  27. (26). Propodeal spines well developed (Fig. 34, right), at least 1/2 length of distance between bases of spines, often as long as distance ............ maryanae new species
    - Propodeal spines small to tiny, total length less than 1/2 distance between bases (Fig 35) ............
    28
  28. (27). Dark brown; propodeal armature consisting of blunt angles (Fig. 35, left), region between propodeal angles with fine transverse rugae; known only from the state of Chihuahua, México, nesting under bark of cottonwood trees ............ adustus new species
    - Light yellow brown; propodeal spines small, but acute (Fig. 35 right), region between propodeal spines punctate; California (in litter) ............ chandleri new species
  29. (15). Head densely and evenly punctate, never with central strip free of sculpture (Fig. 36, left), without striae or rugae, or rarely with punctures in rows that may form weak striae; pale yellow to light brown with black eyes ............30
    - Head usually with striae or rugae as well as punctures (Fig. 36, right), the entire dorsal surface usually feebly shining, often central strip is without sculpture; color yellow, yellow brown to dark brown ............ 35
  30. (29). In profile, node of petiole relatively sharp (Fig. 37) ............ coleenae new species
    - In profile, node of petiole truncate or rounded (Fig. 38) ............
    31
  31. (30). Relatively large species, total length greater than 3 mm; petiolar node broadly rounded in profile (Fig. 38) ............ punctaticeps new species
    - Smaller species, total length less than 3 mm; petiolar node more or less truncate or acute in profile (Figs. 39, 40) ............
    32
  32. (31). Propodeal spines small, but developed; hairs on petiole blunt and thickened (Fig. 39); Texas ............ 33
    - Propodeal spines poorly developed, consisting simply of angles; hairs on petiole fine with relatively sharp tips (Fig. 40); México (Nuevo León) ............. punctatissimus new species
  33. (32) Eyes relatively small (maximum diameter < 0.15 mm), maximum diameter less than distance of anterior edge to base of mandible (Fig. 41, left); recorded only from near Austin and from the Chisos Mountains of western Texas ............ terrigena Wheeler
    - Eyes relatively large (maximum diameter > 0.20 mm), maximum diameter about equal to distance from insertion of mandible (Fig. 41, right); found in deserts in west Texas ............
    34
  34. (33). Color nearly white; dorsum of pronotum with poorly developed rugulae; petiolar node truncate (Fig. 42, left) ............ liebi new species
    - Color pale brown; dorsum of pronotum with distinct rugae; node of petiole rounded (Fig. 42, right) ............ bestelmeyeri new species
  35. (29). Propodeal spines joined at bases by distinct transverse ridge or welt (Fig. 43) which lies at angle between dorsal and posterior faces of propodeum; east central Texas ............ obturator Wheeler
    - Propodeal spines not joined at base by transverse welt; widely distributed ............
    36
  36. (35). Head with rugae as well as punctures (Fig. 36, right); petiolar peduncle elongate and petiole with square node as seen in profile (Fig. 44); Baja California ............ peninsularis Wheeler
    - Head mostly or entirely punctate, or with striae or rugae (Fig. 41, left); petiolar peduncle short (and node may be square in profile) or if somewhat elongate, petiolar node rounded (Fig. 47); widely distributed ............
    37
  37. (36). Postpetiole less than 1.5 times as wide as total width of petiole, as seen from top (Fig. 45) ............ 38
    - Total width of postpetiole at least 1.5 times as wide as total width of petiole (Fig. 46), occasionally twice as wide ............ 43
  38. (37). Petiole and postpetiole with coarse, long, thick, clavate hairs (Fig. 45), about 4 - 10 on petiole and 12 - 20 on postpetiole; dorsum of head with rugae, with intrarugal spaces shining; dorsum and especially sides of mesosoma with well defined rugae; node of petiole truncate (Fig. 47); southeastern Arizona (Cochise Co.) ............ stenotyle Cole
    - Without all of above characteristics; hairs on petiole and postpetiole slightly spatulate, or only blunt tipped; dorsum of head strongly striate, mixed with punctures or with fine rugulae ............
    39
  39. (38). Propodeal spines at least 1/2 as long as distance between bases (Fig. 48 & 49); dark brown in color ............ 40
    - Length of propodeal spines usually less than 1/2 distance between bases, usually consisting of tiny spines or simply angles (Fig 40) (if longer, apex of petiole sharp as seen in profile); pale yellow or light yellowish brown, head and part of gaster may be light-brown ............ 42
  40. (39). Propodeal spines longer than the distance between their bases (Fig. 49, left); petiole with moderately sharp apex (Fig. 48), which is "pinched" as seen from above (Fig. 50, left); postpetiolar node one and one fourth times broader than long, sides subparallel; usually nests in cynipid galls in canyon live oak (Quercus chrysolepis Liebm.) in California ............ gallae M. Smith
    - Propodeal spines about 1/2 to as long as distance between bases (Fig. 49, right); petiolar node rounded or truncate in profile (Fig. 51), apex not "pinched" as above (Fig. 50, right); nests under rocks and duff, or simply in soil, and is common and widely distributed in western U.S.A. ............
    41
  41. (40). Dorsum of pronotum with longitudinal rugae (Fig. 49, right); intrarugal spaces on head of female smooth and shining ............ nevadensis Wheeler
    - Dorsum of pronotum predominantly punctate (Fig. 52, left), with a few striae; intrarugal spaces on head of female punctate ............ lindae new species
  42. (39). Petiole in profile with sharp apex (Fig. 54); propodeal spines nearly 1/2 length of distance between bases; mesosoma with evidence of striae, especially on sides; Colorado, Wyoming ............ furunculus Wheeler
    - Petiole in profile with rounded or somewhat truncated apex (Fig. 56); propodeal spines shorter than 1/2 distance between bases (Fig. 55); mesosoma completely punctate with no evidence of striae (Fig. 55); western North America (CA, NV, AZ, NM, Baja California Norte) ............ andrei Emery
  43. (37). Dorsum of postpetiole coarsely, and predominantly transversely, reticulo - rugose (Fig. 57, left); node of petiole truncate in profile ............ texanus Wheeler
    - Dorsum of postpetiole punctate or granulose (Fig. 57, right), rarely reticulo-rugose, rugae often present on sides of node, node of petiole in profile occasionally with sharp apex (Fig. 54) ............
    44
  44. (43). Postpetiole very large, at least 1.6 X as wide as petiole and half as wide as gaster (Fig. 57, right); New York south to Florida............ davisi Wheeler
    - Postpetiole usually less than 1.6 X as wide as petiole and less than half as wide as gaster; middle and western USA south into western México ............
    45
  45. (44). Sculpture on dorsum of head consisting primarily of striolae or very fine rugulae (or finely punctate) (Fig. 58, left); side of petiole without rugae or rarely with rugulae (Fig. 60); often concolorous pale yellowish - brown (rarely dark brown), gaster often slightly darker ............ 46
    - Sculpture on head consisting of fine rugae (Fig. 58, right); side of petiole with rugae which are not obscured by punctures (Fig. 59); concolorous dark brown; middle and western USA ............ tricarinatus Emery
  46. (45). Side of pronotum weakly shining with well-defined parallel striae (Fig. 60); México (Michoacán and Hidalgo) ............ 47
    - Side of pronotum dull and granulate or punctate, or with poorly defined parallel striae (Fig. 59); southwestern USA and NW México ............ 48
  47. (46). Propodeal spines poorly developed (Fig. 60), but present; rugulae on pronotum well defined and extending posteriorly onto mesonotum ............ rugulosus new species
    - Propodeal spines consisting of tiny angles; fine rugae on pronotum poorly defined, dorsum of mesonotum punctate ............ rugithorax new species
  48. (46). Propodeal armature consisting of simple angles (Fig. 61); light brown ............ carinatus Cole
    - Propodeal spines well developed (Fig. 62), length at least 1/3 distance between bases of the spines; petiole obliquely truncate (Fig. 62); dark brown ............ ............ neomexicanus Wheeler
  49. (6). Propodeal spines short or dentiform (Fig. 63), length less than 1/2 distance between bases; often concolorous dark brown ............ 50
    - Propodeal spines longer than 1/2 distance between bases (Fig. 64); ranging from yellowish-brown to concolorous dark-brown or bicolored ............ 53
  50. (49). Dorsum of head densely punctate, mixed with striae (Fig. 65, left); distributed over much of the United States ............ 51
    - Dorsum of head partially smooth and shining (Fig. 65, right); New Mexico and México ............ 52
  51. (50). Node of petiole broadly rounded (Fig. 66); eastern half of USA (west to Kansas, Oklahoma & Texas) ............ schaumii Roger
    - Node of petiole with sharp apex (Fig. 63) ; known only from California ............ oxynodis new species
  52. (50). Dorsum of pronotum with rugae (Fig. 67, left); bicolored (head and gaster black, mesosoma, legs, petiole & postpetiole orange) ............ emmae new species
    - Dorsum of pronotum ranging from smooth to punctate (Fig. 67, right); concolorous dark brown ............ whitfordi new species
  53. (49). Dorsum of head nearly smooth, shining (Fig. 72, left); propodeal spines often nearly as long as distance between tips (Fig. 68) ............54
    - Entire dorsum of head covered with sculpture (Fig. 72, right); propodeal spines often shorter than distance between tips (Fig. 69) ............ 55
  54. (53). Propodeal spines form an angle of nearly 180° with dorsum of propodeum when viewed in profile (Fig. 70); common and widely distributed in eastern United States ............ longispinosus Roger
    - Propodeal spines form an angle of about 150° with dorsum of propodeum when viewed in profile (Fig. 71); known only from Alabama and North Carolina ............ tuscaloosae Wilson
  55. (53). Head with very delicate longitudinal rugae, not much coarser than intrarugal sculpture and often forming reticulations with it; eastern United States ............ 56
    - Head with coarse longitudinal rugae which are notably heavier than the intrarugal sculpture and do not form reticulations with it (Fig. 72, right); mostly western United States ............ 58
  56. (55). Propodeal spines set close together at bases, spines about twice as long as distance between bases (Fig. 73, left); postpetiole, from above, sub-quadrate, slightly broader than long ............ curvispinosus Mayr
    - Propodeal spines well-separated at bases, about as long as the distance between bases (Fig. 73, right); postpetiole, from above, notably broader than long ............
    57
  57. (56). Propodeal spines of worker and female tapered toward apex, with sharp tip (Fig. 74); female with large, oblong eye (greatest diameter about 0.25 mm, see Fig. 76, left); common and widely distributed in eastern half of USA ............ambiguus Emery
    - Propodeal spines of female blunt tipped (Fig. 75) and of approximately the same diameter (Fig.75) along entire length (worker unknown); female with small, round eye (maximum diameter about 0.12 mm, see Fig. 77); known only from Washington DC, may be workerless parasite of L. curvispinosus ............ minutissimus M. Smith
  58. (55). Intrarugal punctures of head very dense and coarse, areas where they occur dull (Fig. 78, left); southeastern United States ............ 59
    - Intrarugal punctures of head fine and somewhat separated, areas where they occur feebly shining (Fig. 78, right); western United States ............ 60
  59. (58). Dorsum of postpetiole lightly punctate, not completely opaque; dorsum of mesonotum with longitudinal rugae largely replaced by punctures (Fig. 79, left); propodeal spines about half as long as distance between tips ............ bradleyi Wheeler
    - Dorsum of postpetiole heavily punctured and completely opaque; dorsum of mesonotum with longitudinal rugae not replaced by punctures (Fig. 79, right); propodeal spines more than half as long as distance which separates tips ............ smithi Baroni Urbani
  60. (58). Relatively small, total worker length approximately 2.5 mm, yellowish-brown with dorsum of head slightly darker, rarely bicolored; nests under rocks ............ rugatulus Emery
    - Large ants, total worker length over 3 mm; bicolored, head and gaster black, mesosoma dark reddish brown; nests in branches of oak trees ............ josephi new species 7

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