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

 * Petiolar node 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
 * Petiolar node 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, at most only slightly wider than 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

 * Flange at bend of antennal scape a single ridge that begins near antennal insertion and ends immediately above bend
 * Flange at bend of antennal scape with a ridge towards antennal insertion and a "U"-shaped, cup-like structure above bend

22A

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

22B

 * Sculpture on dorsal surface of postpetiole weakly developed medially, 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

 * Flange at bend of antennal scape less extensive, reduced to a narrow (less than scape width), thin band across the outer surface of scape Myrmica fracticornis
 * Flange at bend of antennal scape larger, cup-shaped and slightly wider than scape width

24

 * Petiolar node with distinct dorsal and posterior faces which are separated by a rounded angle; Montana, Wyoming, Utah, Arizona to British Columbia, Nevada, Oregon Myrmica tahoensis
 * Petiolar node with the dorsal and posterior faces rounding gradually into each other, the separation between them indistinct; Nevada, Colorado Myrmica wheelerorum