Key to Myrmecocystus species

The following keys are modified from Snelling 1976 and 1982.

Snelling, R. R. 1976. A revision of the honey ants, genus Myrmecocystus (Hymenoptera: Formicidae). Nat. Hist. Mus. Los Angel. Cty. Sci. Bull. 24: 1-163.

Snelling, R. R. 1982. A revision of the honey ants, genus Myrmecocystus, first supplement (Hymenoptera: Formicidae). Bull. South. Calif. Acad. Sci. 81: 69-86.

The keys are in three parts, representing the three subgenera defined by Snelling. Unfortunately there is no key to the subgenera so you must examine specimens and compare them with the Myrmecocystus subgenus descriptions.

Snelling also provided the following guidance for keying out species: "Worker keys for the subgenera Myrmecocystus s. str. and Eremnocystus should present few problems. Workers in the subgenus Endiodioctes will often prove more troublesome and isolated strays may not key at all well, especially if they are minor workers. Ideally, one should have a nest series reflecting a full gamut of size variation; the key to Endiodioctes is constructed assuming that this is the case."

1

 * Abundantly hairy species: 20+ erect hairs on malar area in frontal view; scape, femora and tibiae with numerous suberect to erect hairs on all surfaces; first three (usually four) terga with dense pubescence (except Myrmecocystus intonsus); HW of major usually in excess of 1.7 mm . . . . . 2


 * Less hairy species: fewer than 20 erect hairs on malar area in frontal view, usually fewer than 6; scape and femora often sparsely hairy; third tergum often sparsely pubescent; HW of major less than 1.7 mm . . . . . 6

2
return to couplet #1
 * Longest occipital hairs usually shorter than EL; longest pronotal hairs as long as or (usually) shorter than EL; longest discal hairs of second tergum less than EL; head of major often strongly orbiculate . . . . . 3


 * Longest occipital, pronotal and discal hairs of second tergum exceeding EL; head of major not orbiculate . . . . . Myrmecocystus melliger

3
return to couplet #2
 * Third tergum, and usually fourth as well, densely pubescent; pronotal hairs variable, but often more than 0.5 x MOD; HW of major in excess of 1.7 mm; head of major orbiculate or not . . . . . 4


 * Third and fourth terga with scattered pubescence only; pronotal hairs stiff, uniform, less than 0.5 x MOD; HW of major less than 1.7 mm; head of major orbiculate . . . . . Myrmecocystus intonsus'

4
return to couplet #3
 * Longest hairs on pronotal dorsum and disc of second tergum no more than 0.5 x MOD, usually less; head of major orbiculate or not . . . . . 5


 * Longest hairs on pronotal dorsum and disc of second tergum at least 0.6 x MOD, usually about 0.75 x MOD; head of major with margins, in frontal view, nearly parallel . . . . . Myrmecocystus mendax

5
return to couplet #4
 * Frontal lobes shiny, closely, sharply punctate, punctures round or weakly ovoid; frons usually with distinct, coarse punctures greater in diameter than hairs arising from them; head of major not, or weakly, orbiculate (Calif., Baja Calif.) . . . . . Myrmecocystus semirufus


 * Frontal lobes dull, irregularly, weakly punctate, punctures often elongate; frons weakly punctate, if at all, punctures, when present not exceeding diameter of their hairs; head of major strongly orbiculate (Tex. To Ariz.) . . . . . Myrmecocystus placodops

6
return to couplet #1
 * Malar area, in frontal view, with six or more erect hairs evenly distributed between eye and base of mandible . . . . . 7


 * Malar area, in frontal view, with not more than four erect hairs, these confined to lower half, near base of mandible . . . . . 11

7
return to couplet #6
 * First three terga uniformly, densely pubescent; clypeus moderately shiny to polished, lightly tessellate to smooth; frontal lobes shiny, sparsely to closely punctate; HW variable . . . . . 8


 * Third tergum apubescent or at least conspicuously less pubescent than first two; clypeus slightly shiny, distinctly tessellate; frontal lobes slightly shiny, distinctly tessellate, with scattered coarse punctures and dense micropunctures; HW of majors 1.03-1.63 mm . . . . . Myrmecocystus intonsus

8
return to couplet #7
 * Tergum IV conspicuously pubescent in specimens with PW in excess of 1.0 mm; erect hairs present over at least half of distance between inner eye margin and antennal socket; punctures of frontal lobes and frons of variable size and irregularly distributed . . . . . 10


 * Tergum IV with pubescence, when present, very widely scattered; erect hairs present only adjacent to inner eye margin, not extending more than 0.25 of distance between eye and antennal socket; punctures of frontal lobes and frons uniformly minute, evenly distributed . . . . . 9

9
return to couplet #8
 * Longest pronotal hairs more than 0.5 x MOD; malar area usually with 12-16 erect hairs; vertex usually conspicuously, though finely, punctate toward sides . . . . . Myrmecocystus romainei


 * Longest pronotal hairs less than 0.5 x MOD; malar area usually with fewer than 12 erect hairs; vertex without punctures at sides . . . . . Myrmecocystus flaviceps

1

 * Antennal scape and dorsum of propodeum without fully erect hairs . . . . . 2


 * Antennal scape, usually, and dorsum of propodeum, always, with some fully erect hairs (propodeal hairs may be short and inconspicuous in Myrmecocystus perimeces; this species has an unusually elongate head, CI 70-81) . . . . . 3

1

 * Dorsal surface of propodeum strongly, angularly projected upward over posterior two-thirds; erect hairs very sparse, with few or none on outer face of hind tibia; upper eye margin little below upper margin of head . . . . . 2


 * Dorsal surface of propodeum either flat or evenly convex; body often abundantly hairy; upper eye margin usually well below upper margin of head . . . . . 3

2
return to couplet #1
 * With at least two erect pronotal hairs as long as apical breadth of scape; first tergum with a few erect hairs on disc; hind tibia with a few erect hairs on outer face beyond basal third . . . . . Myrmecocystus ewarti


 * Erect pronotal hairs, when present, shorter than apical breadth of scape; first tergum without erect discal hairs; hind tibia without erect hairs on outer face beyond basal third . . . . . Myrmecocystus pyramicus

3
return to couplet #1
 * Fully erect hairs conspicuous on thoracic dorsum, discs of first and second terga and on scape and tibiae . . . . . 4


 * No erect hairs on thoracic dorsum, discs of first and second terga, scape or tibiae . . . . . Myrmecocystus christineae

4
return to couplet #3
 * Head, pronotum and gaster with abundant appressed pubescence; mid and hind tibiae usually with numerous erect hairs along apical half of outer face; upper eye margin often distinctly below occipital comer; if metanotal suture impressed, HL exceeds 1.3 mm . . . . . 5


 * Head, pronotum and gaster shiny, with little or no appressed pubescence; mid and hind tibiae with not more than 3 or 4 erect hairs beyond basal third of outer face, usually none; upper eye margin coincident with occipital comer; metanotal suture deeply impressed and dorsal face of propodeum convex . . . . . Myrmecocystus navajo

5
return to couplet #4
 * Large, highly polymorphic species, HL 1.0-2.0 mm or more, usually in excess of 1.3 mm; metanotal suture usually impressed and propodeum as long as high or longer, juncture of dorsal and posterior faces broadly rounded . . . . . 6


 * Smaller, moderately polymorphic species, HL 0.8-1.4 mm; metanotal suture not impressed; propodeum higher than long, juncture of dorsal and posterior faces abruptly rounded, often subangulate . . . . . Myrmecocystus testaceus

6
return to couplet #5
 * Eye with numerous erect hairs which are longer than diameter of ocular facets; mandible with 8 or 9 teeth; color uniformly brownish, gaster a little darker . . . . . Myrmecocystus melanoticus


 * Eye with erect hairs, when present, very diffuse, length less than diameter of ocular facets; mandible with 9 or 10 teeth; color usually distinctly yellow, but may be extensively brownish in southern populations . . . . . Myrmecocystus mexicanus

1

 * Fifth segment of maxillary palp broadest in middle, narrowed basally and apically; hind femur without erect hairs on dorsal surface; hind tibia with hairs decumbent, never fully erect . . . . . 2


 * Fifth segment of maxillary palp broadest well basad of middle, gradually narrowed toward apex or parallel sided; hind femur with erect hairs on dorsal surface; hind tibia with abundant fully erect and suberect hairs . . . . . 5

2
return to couplet #1
 * Antennal scape with decumbent or appressed hairs only except a few erect hairs at tip; ocelli normal, OD less than 0.12 mm . . . . . 3


 * Antennal scape with conspicuous coarse erect and suberect hairs; ocelli large, OD greater than 0.15 mm . . . . . Myrmecocystus navajo

3
return to couplet #2
 * Fourth segment of maxillary palp gradually widened from base to apex; fine punctures of parapsis abundant and uniformly spaced (Figs. 17, 18); side of frontal lobe shiny between close, fine punctures . . . . . 4


 * Fourth segment of maxillary palp distinctly clavate (Fig. 9); fine punctures of parapsis very irregularly spaced (Fig. 16); side of frontal lobe dull and roughened between fine punctures which are at least partially obscured . . . . . Myrmecocystus christineae

4
return to couplet #3
 * Fine punctures of parapsis conspicuously coarser than those of disc of mesoscutum (Fig. 17); first tergum with fewer than 6 erect hairs on disc, often none; interocellar distance about equal to ocellocular distance . . . . . Myrmecocystus pyramicus


 * Fine punctures of parapsis not obviously coarser than those of disc of mesoscutum (Fig. 18); first tergum with at least 12 erect to suberect hairs on disc; interocellar distance less than ocellocular distance . . . . . Myrmecocystus ewarti

5
return to couplet #1
 * Thorax and gaster brown, legs usually yellowish; HW usually less than 1.85 mm; penultimate segment of maxillary palp slender, parallel-sided . . . . . Myrmecocystus testaceus


 * Thorax and gaster light brownish yellow to yellow, legs concolorous with thorax; HW 1.90 mm or more; usually more than 2.0 mm; penultimate segment of maxillary palp distinctly broadest basad . . . . . Myrmecocystus mexicanus