Ants of the subfamily Pseudomyrmecinae:
Keys to the Nearctic species of Pseudomyrmex

Worker Key
Queen Key

There are 11 species of Pseudomyrmex known from the Nearctic region. Ten of these occur in the United States, while one species reaches the margins of the Nearctic region in northeastern Mexico. The revision of Nearctic species by Ward (1985) listed ten species, but an additional species (P. caeciliae) was later recognized as occurring in North America (Ward, 1989).

The keys below make frequent use of morphometric characters. See the preceding link for more details.

Key to Nearctic species of Pseudomyrmex based on the worker caste

Modified from Ward (1985, 1989). This key excludes P. leptosus Ward, which is known only from the queen and male.

1. a. Erect hairs conspicuous on most parts of body, including mesonotum and propodeum .... 2

   b. Erect pilosity very sparse, lacking on mesonotum and (nearly always) propodeum .... 5

2. a. Large, bicolored orange and black species (HW > 1.40); head approximately as wide as long (CI > 0.95); petiole with long anterior peduncle (PLI < 0.55) (Florida; Texas south to South America) .... gracilis (Fabricius)

   b. Small, unicolored brown species (HW < 0.80); head notably longer than wide (CI < 0.80); petiole short (PLI > 0.60) and without long anterior peduncle .... 3

   2a		2b

3. a. Larger species (HW 0.65-0.73), with shorter eyes (REL2 0.65-0.71), and a lower, thinner petiole (PLI 0.67-0.78) (Florida, West Indies; related populations in mainland Neotropics) .... cubaensis (Forel) (s.s.)

   b. Smaller species (HW 0.51-0.68, usually < 0.65), with longer eyes (REL2 0.72-0.82), and a higher, broader petiole (PLI 0.76-1.09) .... 4

   3a		3b

4. a. Head and pronotum densely punctate and predominantly opaque, punctures on upper half of head mostly contiguous and without extensive shiny interspaces (separated by half their diameters or less); averaging larger in size (HW 0.56-0.68) (Florida; Mexico to South America) .... elongatus (Mayr)

   b. Dorsum of head and pronotum with more extensive shiny interspaces; at least some punctures separated by half their diameters or more, especially on upper half of head above compound eye; averaging smaller in size (HW 0.51-0.61) (Texas south to Panama) .... caeciliae (Forel)

5. a. Head and gaster usually dark brown; small species (HW < 0.82), with a deep, wide metanotal groove (arrow in figure below) (MPI 0.046-0.097); dorsal face of propodeum generally shorter than declivitous face (PDI 0.56-1.07) .... 6

   b. Head and gaster golden yellow to orange-brown (fourth abdominal tergite may have darker fuscous patches); variable in size (HW 0.55-1.04), metanotal groove usually relatively shallow (MPI 0.005-0.054); if metanotal groove very deep (MPI >= 0.046), then dorsal face of propodeum notably longer than declivitous face (PDI >= 1.10) .... 7

   5a

6. a. Dorsal face of propodeum about one half to three quarters the length of the declivitous face (PDI 0.56-0.75); petiole with long anterior peduncle, the node somewhat displaced posteriorly (NI 0.57-0.65); petiole and postpetiole very broad (PWI 0.54-0.65; PPWI 1.26-1.54) (Mexico) .... brunneus (F. Smith)

   b. Dorsal face of the propodeum longer (PDI 0.70-1.07) (Figure 14); summit of petiolar node in a more anterior position (NI 0.48-0.060); petiole and postpetiole less broad (PWI 0.40-0.52; PPWI 0.93-1.25) (southeastern United States, south to Costa Rica) .... ejectus (F. Smith)

   6a		6b

7. a. Fourth abdominal tergite (first "gastric" tergite) smooth and strongly shining, more or less devoid of appressed pubescence; vertex of head smooth and shining; broad profemur (FI 0.45-0.52); small species, with relatively long eyes (HW 0.55-0.74; OI 0.49-0.55; REL 0.52-0.61) (Florida, West Indies, Mexico south to Brazil) .... simplex (F. Smith)

   b. Fourth abdominal tergite subopaque, covered with a (usually dense) mat of fine appressed pubescence; vertex of head at least slightly coriarious, weakly shining to subopaque; more slender profemur (FI <= 0.45); generally larger species, with relatively shorter eyes (HW 0.68-1.04; OI 0.54-0.65; REL 0.39-0.54) .... 8

8. a. Eyes short (REL 0.39-0.44); scapes relatively long, subequal to eye length (SI2 0.90-1.00); median (protruded) portion of anterior clypeal margin laterally rounded; frontal carinae relatively well-separated, the minimum distance between them subequal to the basal width of the scape (MFC 0.033-0.066, FCI 0.034-0.070) (southwestern United States, northern Mexico) .... apache Creighton

   b. Eyes longer (REL 0.43-0.54); scapes notably shorter than eye length (SI2 0.68-0.85); median portion of anterior clypeal margin laterally angulate; frontal carinae variable, often more closely contiguous so that the minimum distance between them is notably less than the basal width of the scape (MFC 0.011-0.042, FCI 0.015-0.047) .... 9

   8a		8b

9. a. Larger species (HW 0.87-0.96); frontal carinae relatively well-separated (MFC 0.029-0.042, FCI 0.031-0.047); eyes relatively short (REL 0.43-0.48); median portion of anterior clypeal margin weakly angulate, thus appearing tridentate (Gulf States, Mexico) .... seminole Ward

   b. Smaller species (HW 0.68-0.89); frontal carinae more closely contiguous (MFC 0.011-0.024, FCI 0.015-0.033); eyes averaging a little longer (REL 0.45-0.54); median portion of anterior clypeal margin usually straight (southern United States, south to Costa Rica) .... pallidus (F. Smith)

Key to Nearctic species of Pseudomyrmex based on the queens

1. a. Large, bicolored orange and black species (HW > 1.45); erect pilosity abundant on most parts of the body, including propodeum; petiole with a long anterior peduncle (PLI < 0.55) (Florida, Texas south to South America) .... gracilis (Fabricius)

   b. Smaller species (HW < 1.10); either petiole very short and without a conspicuous peduncle (PLI > 0.55), or erect pilosity sparse (lacking on propodeum) .... 2

2. a. Head densely punctate, and more than 1.5 times as long as wide (CI 0.57-0.64); petiole short (PLI 0.58-0.76); usually some erect hairs on the propodeum .... 3

   b. Head varying from finely punctate, to coriarious, to smooth and shining, and no more than 1.5 times as long as wide (CI 0.66-0.86); petiole relatively long (PLI 0.43-0.58); propodeum essentially lacking erect setae .... 5

3. a. Larger species (HW 0.65-0.73, in a sample of 11 queens); eye length less than one half head length (REL 0.43-0.47, n = 11); petiole moderately long (PLI 0.58-0.67, n = 11) (Florida, West Indies; related populations in mainland Neotropics) .... cubaensis (Forel) (s.s.)

   b. Smaller species (HW 0.51-0.61, n = 25); eye length about one half head length or more (REL 0.48-0.55) and petiole short (PLI 0.65-0.94, n = 25) .... 4

4. a. Head densely punctate and predominantly opaque, punctures on upper half of head mostly subcontiguous and without extensive shiny interspaces; larger on average (HW 0.56-0.61, n = 19), with more elongate eyes (REL 0.51-0.55, n = 19) (Florida; Mexico to South America) .... elongatus (Mayr)

   b. Dorsum of head sublucid, with more extensive shiny interspaces between the punctures; smaller on average, with less elongate eyes (HW 0.51-0.59, REL 0.48-0.50; n = 6) (Texas south to Panama) .... caeciliae (Forel)

5. a. Head and gaster usually dark brown; small species (HW 0.62-0.75); frontal carinae closely contiguous (MFC 0.010-0.018; FCI 0.015-0.026); petiole long and slender, more than twice as long as high (PLI 0.43-0.48) .... 6

   b. Head and gaster golden yellow to orange-brown (small fuscous patches may be present on gaster); mostly larger species (HW 0.57-1.03); if HW < 0.80, then either the frontal carinae tend to be less closely contiguous (MFC 0.016-0.035; FCI 0.022-0.046) and/or the petiole is relatively short (PLI 0.48-0.58) .... 7

6. a. Petiole and postpetiole relatively broad, the latter about 1.25 times as wide as long (PHI 0.72, PWI 0.48, PPWI 1.26, in single specimen examined); frons opaque, fine puncture more or less obscured by coarse coriarious sculpture (Mexico) .... brunneus (F. Smith)

   b. Petiole and postpetiole less broad, the latter about as wide as long (PHI 0.57-0.67, PWI 0.42-0.48, PPWI 1.00-1.12; n = 13); frons usually weakly shining, distinctly punctulate on a weaker coriarious background (southeastern United States, south to Costa Rica) .... ejectus (F. Smith)

7. a. Fourth abdominal tergite (first "gastric" tergite) smooth and shining, appressed pubescence inconspicuous, hairs (if present) separated by about their lengths; vertex of head usually smooth and shining, with scattered fine punctures; small species (HW 0.57-0.75), with contiguous frontal carinae (MFC 0.008-0.021; FCI 0.014-0.029) and relatively long eyes (REL2 0.65-0.80); SI2 0.52-0.68 (n = 17 for this and preceding measurements) (Florida, West Indies, Mexico south to Brazil) .... simplex (F. Smith)

   b. Fourth abdominal tergite weakly shining to subopaque, with a (usually dense) mat of appressed pubescence; either vertex of head weakly shining to subopaque, and coriarious with punctures, or SL about three-quarters of EL (SI2 0.75-0.77); generally larger species (HW 0.66-1.03); frontal carinae less closely contiguous (MFC 0.016-0.095; FCI 0.022-0.094); eyes usually shorter (REL2 0.52-0.71); SI2 0.64-0.95 (n = 61) .... 8

8. a. Larger species (HW 0.85-1.03, HL 1.28-1.46); frontal carinae relatively well separated (MFC 0.053-0.095; FCI 0.052-0.094); eyes relatively short (REL2 0.52-0.58) .... 9

   b. Smaller species (HW 0.66-0.92, HL 0.82-1.15); frontal carinae more closely contiguous (MFC 0.016-0.035; FCI 0.022-0.046); eyes longer (REL2 0.59-0.71) .... 10

9. a. Eye length (EL) more than 1.25 times scape length (SI2 0.70-0.80; n = 10); petiole longer, with a more slender anterior peduncle (PLI 0.43-0.49, PWI 0.41-0.51; n = 10) (Gulf States, Mexico) .... seminole Ward

   b. Eye length less than 1.20 times scape length (SI2 0.85-0.95; n = 10); petiole shorter and broader (PLI 0.49-0.57, PWI 0.54-0.60; n = 10); southwestern United States, northern Mexico .... apache Creighton

10. a. Head, especially upper half, smooth and shining, with scattered fine punctures; occipital margin broadly rounded, so that VI 0.68-0.75 (n = 11); small species (HW 0.67-0.70; n = 11) (Florida) .... leptosus Ward

    b. Head coriarious and weakly shining, punctures coarser; lateral margins of occiput more sharply rounded, giving head a more quadrate shape (VI 0.71-0.88; n = 30); larger species on average (HW 0.66-0.92; n = 30) (southern United States, south to Costa Rica) .... pallidus (F. Smith)

Literature Cited

• Ward, P. S. 1985. The Nearctic species of the genus Pseudomyrmex (Hymenoptera: Formicidae). Quaestiones Entomologicae 21:209-246.
• Ward, P.S. 1989. Systematic studies on pseudomyrmecine ants: revision of the Pseudomyrmex oculatus and P. subtilissimus species groups, with taxonomic comments on other species. Quaestiones Entomologicae 25:393-468.

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Philip S. Ward Department of Entomology and Center for Population Biology University of California at Davis Davis, CA 95616, USA email: psward@ucdavis.edu

http://entomology.ucdavis.edu/faculty/ward/psnea.html last modified 22 October 2002