Key to United States species of Pseudomyrmex based on the worker caste. Modified from Ward (1985, 1989) and Keys to the Nearctic species of Pseudomyrmex.
This key excludes Pseudomyrmex leptosus Ward, which is known only from the queen and male.
- Erect hairs conspicuous on most parts of body, including mesonotum and propodeum => 2
- Erect pilosity very sparse, lacking on mesonotum and (nearly always) propodeum => 5
- 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) => Pseudomyrmex gracilis
- 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
- 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) => Pseudomyrmex cubaensis
- 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
- 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) => Pseudomyrmex elongatus
- 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) => Pseudomyrmex caeciliae
- 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) => Pseudomyrmex ejectus
- 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) => 6
- 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) => Pseudomyrmex simplex
- 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) => 7
- 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) => Pseudomyrmex apache
- 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) => 8
- 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) => Pseudomyrmex seminole
- 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) => Pseudomyrmex pallidus
- 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.