Key to Pseudomyrmex elongatulus group species

This key to the workers and queens of the Pseudomyrmex elongatulus group is based on Ward & Branstetter (2022).

See also the Key to Pseudomyrmex species groups.

This key is based primarily on characteristics of workers but we have attempted to incorporate queen features as far as possible. Because queens are less well known, sample sizes are included for all queen measurements. Unless otherwise noted, sample sizes are the same for all measurements cited within a given lug of a couplet. For two species (Pseudomyrmex capillatus, Pseudomyrmex veracruzensis) queens are unknown. Two other species (Pseudomyrmex comitator, Pseudomyrmex ereptor) are known only from queens and are assumed to be workerless social parasites; they are treated at the beginning of the key.

1

 * Queens only; small (HL 1.00–1.01, LHT 0.69–0.70; n = 2) with short, high petiole (PLI 0.67–0.83) (Fig. 9); dark brownish-black; apparent workerless inquiline, known only from Chiapas, Mexico Pseudomyrmex comitator
 * Workers and queens, or queens only; queens larger (HL 1.19–1.49, LHT 0.76–1.12; n = 41), with more slender petiole (PLI 0.42–0.61); color variable

2

 * Queens only; mandibles smooth and shiny, with scattered punctures; postpetiole very broad, appearing ovorectangular in dorsal view (PPW/LHT 1.01; n = 1) (Fig. 12); light orange-brown; apparent workerless inquiline, known only from Veracruz, Mexico Pseudomyrmex ereptor
 * Workers and queens; mandibles usually striate; queen and worker postpetiole more slender, pyriform in dorsal view (queen PPW/LHT 0.66–0.91; n = 40); color variable

3

 * Head relatively broad (worker CI 0.90–0.96; queen CI 0.81–0.84 (n = 5)), with large eyes, whose length exceeds 0.5× head length (worker REL 0.54–0.59; queen REL 0.53–0.54) (Fig. 17); large species (worker HW 1.12–1.21; queen HW 1.18–1.24); southern Mexico to Honduras Pseudomyrmex salvini
 * Head more elongate (worker CI 0.67–0.90; queen CI 0.55–0.80 (n = 35)); eyes proportionately smaller, eye length subequal to, or less than, head length (worker REL 0.38–0.53; queen REL 0.38–0.48); smaller in size (worker HW 0.82–1.09; queen HW 0.76–1.11 (n = 33)), except for one uncommon Costa Rican species with worker HW 1.03–1.20 and queen HW 1.15–1.18 (n = 2)

4

 * Standing pilosity common on most of body, present on mesonotum and propodeum as well as pronotum (worker MSC 25-39; queen unknown but expected to have MSC ~35) (Fig. 13); body dark-brown, the scapes, mandibles, anterior quarter of head capsule, protibia and protarsus a contrasting light yellowish-brown; western Mexico Pseudomyrmex capillatus
 * Standing pilosity sparse, absent from worker and queen propodeum, and almost always absent from worker mesonotum (worker MSC 2–8, queen MSC 11–23 (n = 35)); color variable, not matching the above pattern

5

 * In profile, worker with pronounced metanotal groove and with dorsal face of propodeum convex and rounding insensibly into the declivitous face (Fig. 16); large species (worker HW 1.03–1.20; queen HW 1.15–1.18 (n = 2), with proportionately longer legs (worker FL 0.84–0.99, worker LHT 0.96–1.09; queen FL 0.97–0.99, queen LHT 1.03–1.07) and elongate eyes (worker REL 0.48–0.51; queen REL 0.48); head, propodeum, and gaster dark brown, other parts of body with variably lighter coloration (medium brown to yellow-brown); known only from Costa Rican cloud forest Pseudomyrmex nimbus
 * Worker metanonotal groove usually weakly impressed or absent, but if conspicuously developed then propodeum more flattened, and dorsal face better differentiated from declivitous face (Fig. 10); disagreeing with one or more other characters: either smaller and/or with shorter legs and eyes and/or different color pattern; queen REL 0.38–0.46 (n = 33); occurring from southern United States to Costa Rica

6

 * Head very elongate (worker CI 0.67–0.69; queen CI 0.55–0.59 (n = 2)) (Fig. 14); profemur short and robust (worker FI 0.46–0.49, worker FW/HW 0.41–0.44; queen FI 0.47–0.49, queen FW/HW 0.45–0.46); southern Mexico to Honduras Pseudomyrmex exoratus
 * Head less elongate (worker CI 0.79–0.90; queen CI 0.68–0.76 (n = 20)); profemur generally more slender (worker FI 0.38–0.47, worker FW/HW 0.30–0.38; queen FI 0.42–0.49, queen FW/HW 0.34–0.41)

7

 * Worker with well-developed metanotal groove, conspicuous in profile (Fig. 10); in full-face view, head with rounded posterolateral corners and elongate eyes (worker REL 0.47–0.53; queen REL 0.44–0.46 (n = 5)) (Figs. 10 and 11); petiole slender, elongate-triangular in profile (worker PLI 0.44–0.52; queen PLI 0.45–0.51) (Figs. 10 and 11); leg moderately long, worker LHT/HL 0.74–0.79, queen LHT/HL 0.64–0.67; typically light yellow- to orange-brown with transverse infuscation on gaster, but head and mesosoma more infuscated in southern parts of range; eastern Mexico to Guatemala and Belize Pseudomyrmex elongatulus
 * Worker metanotal groove moderately developed to absent; not matching the combination of other features

8

 * Body unicolorous yellow-orange to ferrugineus-brown (gaster may have transverse fuscous patches)
 * Body either bicolored (dark gaster contrasting with lighter colored mesosoma) or predominantly brown to brownish-black, the mesosoma either concolorous with head and gaster or moderately lighter

9

 * Body ferrugineus-brown (Fig. 18); relatively large species (worker HW 0.97–1.07; queen unknown) with rather elongate petiole (worker PL 0.65–0.77, worker PLI 0.44–0.49); higher elevations, Veracruz, Mexico Pseudomyrmex veracruzensis
 * Body light yellow- to orange-brown; size variable, usually smaller (worker HW 0.82–1.00; queen HW 0.86–1.04 (n = 15)) and with less elongate petiole (worker PL 0.49–0.66, worker PLI 0.46–0.61; queen PL 0.71–0.84, queen PLI 0.47–0.58)

10

 * Worker metanotal groove very weakly impressed, scarcely discernable in profile (Fig. 15); eyes elongate (worker REL 0.45–0.48; queen REL 0.45–0.46 (n = 6)); yellow-orange, with conspicuous anterolateral patches on fourth abdominal (first gastric) tergite and dark transverse bands on abdominal tergites 5–6 (gastric tergites 2–3); Chiapas to Costa Rica Pseudomyrmex fasciatus
 * Worker metanotal groove somewhat better developed, more obvious in profile (Figs. 4 and 5); eyes less elongate, on average (worker REL 0.40–0.47; queen REL 0.38–0.44 (n = 9)); yellow-orange, with at most anterolateral fuscous patches on fourth abdominal (first gastric) tergite, but without transverse bands on succeeding segments (tip of gaster may be infuscated)

11

 * In profile, worker propodeum and petiole more rounded (Fig. 5); eye relatively elongate (worker REL2 0.52–0.58; queen REL2 0.56–0.58 (n = 3)); worker petiole more slender (worker PLI 0.49–0.57); northwestern Mexico to Oaxaca Pseudomyrmex arcanus
 * In profile, worker propodeum and petiole more angular (Fig. 4); eye shorter (worker REL2 0.48–0.53; queen REL2 0.53–0.55 (n = 6)); worker petiole more robust (worker PLI 0.55–0.61) (Fig. 3 [bivariate plots]); southwestern United States and adjacent northern Mexico Pseudomyrmex apache

12

 * Bicolored: dark brownish-black gaster contrasting with light orange-brown mesosoma (head may be dark or light); worker metanotal groove present and clearly discernable in profile (Fig. 6); eye shorter (worker REL 0.38–0.44; queen REL 0.40–0.42 (n = 3)); western Mexico Pseudomyrmex championi
 * Body more uniformly dark brownish-black, at most mesosoma moderately lighter; worker metanotal groove very weakly impressed, barely discernable in profile (Fig. 7); eye usually longer (worker REL 0.45–0.48; queen REL 0.42–0.46 (n = 8)) but eye shorter in one divergent sample from Guatemala where worker REL 0.43–0.45 (see discussion in text); Chiapas, Mexico to Nicaragua Pseudomyrmex cognatus