Key to Pseudomyrmex species groups

This key is based on: Ward, P.S. 2017. A review of the Pseudomyrmex ferrugineus and Pseudomyrmex goeldii species groups: acacia-ants and relatives (Hymenoptera: Formicidae). Zootaxa. 4227:524–542. (doi: 10.11646/zootaxa.4227.4.3).

This is a provisional key and is based on the worker caste. The primary purpose of this key is to permit recognition, within the ant genus Pseudomyrmex, of the P. ferrugineus group, P. goeldii group, and closely related species; such taxa are highlighted in bold font in the key. Species groups have been modified from those recognized in Ward (1989), to reflect more recent knowledge of phylogenetic relationships (Ward & Downie 2005; Chomicki et al. 2015; Ward 2017). The key also includes taxonomically isolated species that are unplaced to a group.

1

Frontal carinae closely contiguous, elevated anterodorsally, and directed forward onto the median clypeal lobe rather than fus-ing anterolaterally with the antennal sclerites (Fig. 7a; see also Ward 1989, figs. 18–19) . . . . . 2

Frontal carinae variably separated, not elevated anterodorsally, directed anterolaterally and fusing with the antennal sclerites (Fig. 2a; see also Ward 1989, figs 16–17) . . . . . 3

2

return to couplet #1

Median clypeal lobe laterally angulate (Fig. 7a); head moderately elongate (CI 0.69–0.85); standing pilosity lacking on propodeum . . . . . Pseudomyrmex goeldii group

Median clypeal lobe laterally rounded; head usually more elongate (CI 0.56–0.73); a pair of long hairs present at the juncture of the dorsal and declivitous faces of the propodeum . . . . . Pseudomyrmex subtilissimus group

3

return to couplet #1

Standing pilosity moderately common to abundant on most parts of body, including mesosoma dorsum (Fig. 2b); MSC usually >12, but if slightly less (7–12) then the standing hairs scattered and mostly shorter than the maximum dorsoventral width of the metatibia . . . . . 4

Standing pilosity sparse on most of body, the hairs on mesosoma dorsum typically arranged as 1–2 and 0–1 isolated pairs on the pronotum and propodeum, respectively; MSC usually <8; very rarely (some sericeus group species; see characterization of the group in couplet 23) MSC 8–12 as a result of additional hairs on the pronotum and mesonotum, but in that case hairs tend-ing to occur as isolated pairs, whose length exceeds the maximum dorsoventral width of metatibia . . . . . 22

4

return to couplet #3

Large species (HW 1.38–1.90) with opaque head and relatively small eyes (REL 0.42–0.46); pronotum with pronounced lat-eral margination; metanotal groove lacking or very weakly impressed; palp formula 6,4; confined to southern Mexico and northern Central America . . . . . Pseudomyrmex rufomedius group

Size and head sculpture variable but if HW >1.35 then either eyes more elongate (REL >0.48) and/or pronotum laterally rounded; metanotal groove generally well developed; palp formula variable; widespread . . . . . 5

5

return to couplet #4

Standing pilosity common on the outer (extensor) surface of the mesotibia and metatibia, (HTC + MTC) >10; the tibial hairs usually long and conspicuous with their maximum length being subequal to, or greater than, the maximum dorsoventral width of the tibia (sometimes hairs shorter, but still distinct from background pubescence, if latter present) . . . . . 6

Tibial pilosity sparse, (HTC+MTC) usually <8 but if greater then hairs inconspicuous and tending to grade into a background of appressed and subdecumbent pubescence . . . . . 11

6

return to couplet #5

Propodeum depressed downward, the dorsal and declivitous faces essentially undifferentiated and appearing in profile as a single convex slope, which contacts the propodeal spiracle; head smooth and shiny, with widely scattered punctulae . . . . . Pseudomyrmex depressus

Propodeum not depressed downward, the dorsal and declivitous faces differentiated; propodeal spiracle situated on the side of the propodeum, below the level of the propodeal dorsum; head variable, usually more densely sculptured . . . . .7

7

return to couplet #6

Eyes elongate, more than half the head length (REL 0.52–0.67); petiole usually slender, width rarely as much as three-quarters of the length (PWI 0.34–0.75); palp formula 6,4 . . . . . Pseudomyrmex gracilis group (except Pseudomyrmex simulans)

Eyes relatively short, less than half the head length (REL 0.32–0.48); petiole usually broader (PWI 0.66–1.40); palp formula variable . . . . . 8

8

return to couplet #7

Head notably broader than long (CI 1.08–1.16); compound eye located on the posterior third of head; body pilosity long and abundant, MSC approximately 95–150, HTC 25–50 . . . . . Pseudomyrmex kuenckeli

Head usually longer than broad, less commonly as broad as long (CI 0.70–1.04); compound eye positioned about the middle of the side of the head; body pilosity less abundant, MSC <90, HTC <25 . . . . . 9

9

return to couplet #8

Scape and funicular segments very short (SI 0.39–0.43); punctures on upper third of head sparse, of uneven density, mostly small and separated by many diameters, leaving extensive smooth interspaces; palp formula 4,3; Tachigali inhabitants . . . . . Pseudomyrmex concolor group (except Pseudomyrmex tachigaliae)

Scape and funicular segments longer (SI 0.42–0.50); punctures on upper third of head moderately dense, uniformly dispersed, most punctures separated by one to several diameters; palp formula 6,4 or 5,3; nesting in dead stems, live stems, or domatia, but not in Tachigali . . . . . 10

10

return to couplet #9

Smaller species, HW (0.73–0.94); petiole relatively slender (DPW/HW 0.32–0.39, DPW/LHT 0.40–0.46); Mexico to Costa Rica . . . . . Pseudomyrmex fervidus group (except Pseudomyrmex hesperius)

Larger species, on average (HW 0.74–1.51); if HW <0.95 then petiole broader (DPW/HW 0.39–0.50, DPW/LHT 0.48–0.58); widespread, mostly in South America . . . . . Pseudomyrmex triplarinus group

11

return to couplet #5

Median clypeal lobe laterally angulate (Fig. 2a) . . . . . 12

Median clypeal lobe laterally rounded . . . . . 14

12

return to couplet #11

Petiole relatively short (PLI 0.72–0.82), lacking anterior peduncle; Tachigali inhabitant . . . . . Pseudomyrmex tachigaliae (Pseudomyrmex concolor group)

Petiole more elongate (PLI 0.47–0.70), with weakly to strongly differentiated anterior peduncle; nesting habits variable, not Tachigali inhabitant . . . . . 13

13

return to couplet #12

Small species (HW 0.78–0.86), with very elongate eyes (REL 0.60–0.62) and robust profemur (FI 0.48–0.53); nesting in dead twigs . . . . . Pseudomyrmex oki (Pseudomyrmex pallidus group) (in part - also #27)

Larger species (HW 0.94–1.26), with less elongate eyes (REL 0.42–0.55) and more slender profemur (FI 0.35–0.46); nesting habits variable, most species inhabiting swollen-thorn acacias (Vachellia) . . . . . Pseudomyrmex ferrugineus group (in part - also #20)

14

return to couplet #11

Standing pilosity present on the proximal funicular segments and (as numerous rather short and inconspicuous hairs) on the outer surface of the mesotibia and metatibia; body pubescence thick and partly decumbent giving worker a “scruffy” appear-ance; eyes relatively short (REL <0.50); anteroventral postpetiolar process well developed . . . . . Pseudomyrmex subater (Pseudomyrmex duckei group)

Without the preceding patterns of pilosity; if body pubescence conspicuously thick and decumbent then eyes more elongate (REL >0.50) and anteroventral postpetiolar process not developed . . . . . 15

15

return to couplet #14

Eyes elongate, about one half head length or more (REL 0.48–0.62); petiole relatively short and high (PLI 0.75–1.09); EL/PL 1.09–1.59; palp formula 6,3, reduced to 5,3 in the smallest species (HW <0.68) . . . . . Pseudomyrmex oculatus group

Eyes shorter (REL <0.48) and/or petiole longer (PLI <0.71); EL/PL usually less than 1.05; palp formula variable, not 6,3 . . . . . 16

16

return to couplet #15

Head sublucid to lucid; sculpture on upper third of head between ocelli and compound eye consisting of scattered minute or medium-sized punctures separated by their diameters or more, the interspaces smooth, shiny and unsculptured . . . . . 17

Head opaque to sublucid, sculpture consisting of contiguous punctulae (separated by less than their diameters) or with punctu-lae separated by coriarious sculpture, smooth shiny interspaces largely lacking . . . . . 19

17

return to couplet #16

Small species (HW 0.65–0.69) with relatively small eyes (REL 0.43–0.46) and a short apedunculate petiole (PLI 0.73–0.77); western Mexico . . . . . Pseudomyrmex hesperius (Pseudomyrmex fervidus group)

Larger species (HW >0.70) with more elongate eyes (REL 0.48–0.59) and longer petiole (PLI 0.50–0.69) . . . . . 18

18

return to couplet #17

Head elongate (CI 0.75–0.82), eyes shorter (REL 0.48–0.53) and petiole longer (PLI 0.50–0.57); punctulae on head minute and inconspicuous, even under 50× magnification; palp formula 5,4 . . . . . Pseudomyrmex filiformis

Head broader (CI 0.81–0.93) with longer eyes (REL 0.56–0.59) and shorter petiole (PLI 0.59–0.69); punctures on head vari-able, minute and sparse or conspicuous and dense; palp formula 6,4 . . . . . Pseudomyrmex duckei group (except Pseudomyrmex subater)

19

return to couplet #16

Larger species (HW 1.22–1.34) with elongate eyes (REL 0.52–0.55); pronotum laterally submarginate; Panama . . . . . Pseudomyrmex simulans (Pseudomyrmex gracilis group)

Smaller species (HW 0.74–1.21); eye size variable (REL 0.40–0.57); pronotum laterally rounded; widespread . . . . . 20

20

return to couplet #19

Frontal carinae closely contiguous, separately by less than basal scape width (FCI 0.022–0.045); palp formula 6,4; usually nesting in dead twigs; predominantly South American in distribution . . . . . 21

Frontal carinae less closely contiguous, usually separated by about basal scape width (FCI 0.042–0.101); palp formula 5,3 or 4,3; nesting in swollen-thorn acacias (Vachellia); restricted to Mesoamerica . . . . . Pseudomyrmex ferrugineus group (in part - also #13)

21

return to couplet #20

Eyes shorter (REL 0.45–0.46) and petiole longer (EL/PL 0.82–0.84); endemic to western Mexico . . . . . undescribed species (Pseudomyrmex elongatulus group) (in part - also #26)

Eyes longer (REL 0.47–0.57) and petiole shorter (EL/PL 0.91–1.20); distributed from Costa Rica to Brazil and Argentina . . . . . Pseudomyrmex pallens group (in part - also #26)

22

return to couplet #3

Median clypeal lobe laterally rounded . . . . . 23

Median clypeal lobe laterally angulate (as in Fig. 2a) . . . . . 27

23

return to couplet #22

Masticatory margin of mandibles with 8–10 teeth or denticles; body covered with a very fine appressed pubescence, giving the integument a silky appearance; eyes very long (REL 0.56–0.70); petiole short, high, and broad (PLI 0.86–1.26) . . . . . Pseudomyrmex sericeus group

Masticatory margin of mandibles with 5–6 teeth; without the combination of other characters . . . . . 24

24

return to couplet #23

Head smooth, shiny, with scattered fine punctulae; metanotal groove deeply impressed . . . . . Pseudomyrmex perboscii

Head subopaque to opaque, with densely punctulate or punctulate-coriarious sculpture; metanotal groove moderately impressed or absent . . . . . 25

25

return to couplet #24

Large species (HW 1.16–1.42, LHT 1.01–1.28), with elongate eyes (REL 0.56–0.74); pronotal humeri subangulate . . . . . Pseudomyrmex tenuis group

Smaller species (HW 0.62–1.20, LHT 0.58–1.05); eyes usually shorter (REL 0.39–0.58); pronotal humeri rounded . . . . . 26

26

return to couplet #25

Eyes smaller, on average (REL2 0.48–0.60); endemic to Mesoamerica (Mexico to Costa Rica) . . . . . Pseudomyrmex elongatulus group (in part - also #21)

Eyes larger, on average (REL2 0.52–0.75); endemic to South America . . . . . Pseudomyrmex pallens group (in part - also #21)

27

return to couplet #22

Masticatory margin of mandible with 6 teeth; palp formula 6,3; endemic to Hispaniola . . . . . Pseudomyrmex haytianus

Masticatory margin of mandible with 5 teeth; palp formula 5,3 or 4,3; widespread . . . . . Pseudomyrmex pallidus group (in part - also #13)