Key to Myrmica of North America

This key to North American species of Myrmica is a work-in-progress and should be used as a guide only. This group is in serious need of taxonomic work and this key is a small contrubution to this effort.

1

 * Node of petiole high, distinctly set off from anterior and posterior peduncles and angular at crest; ventral surface of petiole with distinct, obtusely angular impression formed by the junction of the anterior and posterior peduncles; Arizona Myrmica wheeleri
 * Node of petiole not distinctly set off from anterior and posterior peduncles or, if so, it is low and much rounded above; ventral surface of petiole straight or very feebly convex

2

 * Outer edge of frontal lobe feebly convex throughout most of its length and fusing with head without marked posterior incision; frontal area distinct, not crossed by rugae, usually smooth and strongly shining; Quebec, Maine, Massachusetts, Rhode Island Myrmica rubra,  Myrmica rubra neolaevinodis
 * Outer edge of frontal lobe strongly convex or angular in front, or deeply incised behind, or both; frontal area obscured by rugae, never completely smooth and shining (except in M. punctiventris)

3

 * Frontal lobes narrow, scarcely or not at all projecting above antennal fossae; insertions of antennae exposed when head is viewed from above; Tennessee, Mississippi, Illinois Myrmica spatulata
 * Frontal lobes strongly projecting out over antennal fossae; insertions of antennae hidden when head is viewed from above

4

 * Antennal scape evenly curved at base, upper surface never forming right angle at bend (sometimes about 80°); lamina, if present, low and inconspicuous
 * Antennal scape sharply bent at base, upper surface forming right angle or nearly so; lamina always present and obvious, of varying shapes

5

 * Lateral portion of clypeus raised into carina which forms abrupt, semi-circular boundary at front of antennal fossa (as in Tetramorium) Myrmica rugiventris
 * Clypeus not as above

6A

 * Frontal area mostly smooth and glossy and with at most 1 or 2 short posterior rugae which are less than half the length of the frontal area
 * Frontal area roughly sculptured, with several rugae which extend at least 1/2 its length

6B

 * First gastric segment without coarse, large punctures; propodeal spines elongated with a narrow, thin base; California Myrmica punctinops
 * First gastric segment with coarse, large piliferous punctures; propodeal spines short and dentiform with a large, thick base; eastern North America Myrmica semiparasitica

6

 * Mesonotum raised above the dorsal surface of propodeum so that they fall on separate lines and the metanotal groove forms a step between them; gaster with numerous coarse punctures with diameters at least 5X diameter of hairs arising from them
 * Mesonotum and dorsal surface of propodeum forming a continuous surface (which is interrupted by the metanotal groove); gaster with fine punctures, whose diameter is less than 3X diameters of hairs

7

 * Antennal scapes surpassing occipital margin by an amount equal to their greatest thickness; propodeal spines distinctly longer than the distance separating their tips and slightly deflected downward; dorsal surface of head coarsely striated, rugae high and thick with flattened top in cross section; frontal lobes smaller, difference between maximum and minimum width usually < 0.12 mm; color piceous brown; length 4.0-4.7 mm; Massachusetts to Georgia to Iowa, Nebraska, Arkansas, Texas Myrmica punctiventris
 * Antennal scapes barely surpassing occipital margin; propodeal spines shorter, about equal to the distance separating their tips, not deflected downward; dorsal surface of head delicately striated, rugulae low and rounded in cross section; frontal lobes larger, difference between maximum and minimum width usually > 0.12 mm; color brownish yellow; length 3.5-4.0 mm; Massachusetts to South Carolina, west to Ohio, Oklahoma, Mississippi Myrmica pinetorum

8

 * Gaster with longitudinal striae extending about 2/3 length of first gastral tergum, sparsely, but distinctly; punctate; inquiline in nest of Myrmica striolagaster; Texas (Davis Mts.) Myrmica colax
 * Gaster without longitudinal striae

9

 * Frontal lobes angular, strongly expanded laterally and slightly deflected downwards towards the scape, their widest point at or posterior of antennal insertions
 * Frontal lobes rounded and relatively narrow, moderately to strongly elevated away from scape, their widest point anterior of antennal insertions

11

 * Postpetiole with shining dorsal area that is largely free from rugae; average size of workers 3.5 mm; Alaska, Quebec Myrmica alaskensis
 * Postpetiole ordinarily covered with rugae, rarely with dorsal area free from rugae, but in such cases this area is not shining; average size of workers at least 4.5 mm; Labrador south to New Jersey, west to Rocky Mountains, Wyoming, New Mexico Myrmica incompleta

13

 * Propodeal spines slightly less than one-half as long as distance which separates tips; color variable, but often orange-yellow; North Dakota, Nebraska to New Mexico, west to Alberta, Idaho Myrmica brevispinosa
 * Propodeal spines more than ½ as long as distance which separates tips; color dark brown

14

 * Area between lateral ocellus and eye of male mostly punctate; Newfoundland to mountains of Colorado, Wyoming, New Mexico Myrmica discontinua
 * Area between lateral ocellus and eye mostly with reticulate rugae; eastern Mexico (Nuevo Leon, Coahuila south to Veracruz) Myrmica mexicana

15

 * Flange at bend of antennal scape continuing a short distance along scape towards tip Myrmica nearctica
 * Flange at bend of antennal scape transverse and sometimes collar-like, never elongate and rarely extending along scape towards tip (when present the extension is low and short compared to remaining flange)

17

 * Scape covered with longitudinal rugae; gaster with longitudinal striae on first tergum, obvious at least near point of attachment of post petiole (gradient exists with less developed striae in western populations); gaster with coarse punctures with diameters about 5X diameter of hairs; Arizona (Chiricahua Mountains), New Mexico (entire state), West Texas, Chihuahua (entire state), Colorado Myrmica striolagaster
 * Scape usually with fine sculpture, mostly punctate; gaster without striae and with punctures whose diameter is less than 3X diameter of hairs

18

 * Ventral surface of postpetiole seen in profile flat or nearly so and not forming anterior projection; antennal scapes of male as long or longer than following 4 segments together and straight at base; Quebec, Maine to North Carolina, Tennessee to Manitoba, Colorado, Utah, Arizona Myrmica americana
 * Ventral surface of postpetiole seen in profile convex or forming prominent anterior projection that thrusts forward under anterior peduncle; antennal scapes of male bent at base, or if straight they are distinctly shorter than above

19

 * Flange at bend of antennal scape large (much broader than scape itself) and semicircular, surrounding scape at bend
 * Flange at bend of antennal scape small, sometimes cup-like, similar in width to scape and never surrounding it

20

 * Flange at bend of antennal scape under-cut on inner face, forming a distinct hook; Colorado, New Mexico, Arizona, Utah Myrmica hamulata
 * Flange at bend of antennal scape with inner face rounding uniformly into scape

21A

 * Petiolar node with distinct dorsal and posterior faces which are separated by a rounded angle Myrmica trullicornis
 * Petiolar node with a relatively long dorsal face with rounds gradually into a short, often indistinct, posterior face, the separation of these faces minimal or absent

21B

 * Body larger (head width greater than 0.90mm); in dorsal view propodeal spines generally diverging towards their tips, occasionally parallel, never converging; flange at bend of antennal scape distal (towards tip) of bend, not extending towards condylar bulb and antennal insertion Myrmica crassirugis
 * Body smaller (head width less than 0.85mm); in dorsal view propodeal spines generally converging towards their tips, occasionally parallel or diverging; flange at bend of antennal scape extending basally towards condylar bulb and antennal insertion Myrmica monticola

22

 * Lamina of antennal scape small and diagonally transverse on upper surface of scape, but continued as prominent transparent flange along inner surface of that part of scape that lies below bend; antennal scape of male straight at base and as long as 3 following segments taken together)
 * Lamina not forming prominent median flange as above or if small median flange is present, lamina not transverse on the upper surface of scape

22A

 * Lamina of antennal scape more extensive, extending slightly distally of and beyond bend
 * Lamina less extensive, ending at or just before bend; Newfoundland to Georgia west to Manitoba, Idaho, Colorado, Arizona Myrmica latifrons

22B

 * Sculpture on dorsal surface of postpetiole weakly developed medailly, more strongly developed laterally; widespread Myrmica detritinodis
 * Sculpture on dorsal surface of postpetiole uniformly developed across entire width

22C

 * Body smaller; promesonotum uniformly convex; dorsal surface of propodeum uniformly convex; interrugal sculpturing on head weakly developed and more shiny, especially posterior of antennal insertion; North Carolina, Massachusetts, Illinois, Maine, Michigan, D.C., New Jersey, New York, Missouri, Indiana, Georgia, Iowa, Connecticut Myrmica species "smitha"
 * Body larger; promesonotum strongly convex anteriroly (immediately posterior of collar) and weakly convex posteriorly (along the dorsal surface); dorsal surface of propodeum more strongly arched anteriorly, weakly convex to nearly flat posteriorly; interrugal sculpturing on head well developed and less shiny, especially posterior of antennal insertion; Massachusetts, Maine, New York Myrmica species "sculp"

23

 * Propodal spines slightly, but distinctly bent downward (spines on single ant may be different); mesosoma reddish-yellow, head and gaster piceous; antennal scape of male straight at base and as long as following 3 segments together; Montana, Wyoming, Utah, Arizona to British Columbia, Nevada, Oregon Myrmica tahoensis
 * Propodal spines straight; color not as above; antennal scape of male bent at base and at least as long as following 5 segments together

24

 * Antennal lamina encircling bend of scape in form of spoon-like or saucer-like flange; antennal scape of male abruptly bent at base with upper surface distinctly angulate at bend; propodal spines of male well-developed, propodeum with prominent rugae; CO, NM, UT, AZ, N to Alaska Myrmica lobifrons
 * Antennal lamina small, transverse, forming angular tooth-like projection on inner side of bend; antennal scape of male gradually bent at base and not forming distinct angle at bend; propodal spines of male reduced to rounded angles, rugae of propodeum very feeble or lacking; Newfoundland south to Tennessee, Ohio, west to Rocky Mountains, Colorado, New Mexico, Utah, Arizona Myrmica fracticornis