Stenamma callipygium

Stenamma callipygium has been collected by sifting leaf litter, beating vegetation and baiting with cookie bait. In addition, a single worker was found in a flight intercept trap placed underneath a Malaise trap. This species is a cloud forest specialist known from 1630–1750 m elevation. Very few Stenamma species are known from beating samples, suggesting that this species may nest or at least forage arboreally. The diversity of collecting methods that have retrieved this species suggests that it is an active forager. It is surprising, however, that out of the over 100 leaf litter samples collected at the Biotopo Quetzal by the LLAMA project, only one sample had S. callipygium. (Branstetter 2013)

Identification
Branstetter (2013) - Integument mostly black; medium-sized species (see HL, ML, PrW below); gaster with an elongate anterior constriction, with anterolateral margins of gaster forming hard shoulder-like angles (best viewed dorsally); median lobe of the clypeus projecting out over mandibles, forming a well-defined, blunt apex; basal margin of mandible sinuous, but without a basal notch or deep depression; basal third of mandible distinctly attenuated (dorsoventrally thinned); face with dense fan of carinulae extending to posterior and lateral margins of head; eye large (EL 0.14–0.19, REL 20–24), oval-shaped, with 9–10 ommatidia at greatest diameter; propodeal spines tuberculate (PSL 0.08–0.10, PSI 1.0–1.4); setae on gastral tergites moderately long and sparse, mostly suberect; frontal lobes of moderate width (FLD 0.16–0.21, FLI 22–27), not covering torular lobes in full-face view. Similar species: Stenamma atribellum.

Stenamma callipygium and Stenamma atribellum are sister species and make up the atribellum species group. The diagnostic character state of this group is the elongate gastral constriction. Stenamma callipygium is easy to distinguish from S. atribellum by its median clypeal tooth and carinulate sculpture

Distribution based on Regional Taxon Lists
Neotropical Region: Guatemala.

Biology
The oddly shaped clypeus and mandible of this species is unique within Stenamma and begs for explanation. Most likely the projecting clypeal tooth is used for the capture or maceration of a specific prey type.

Castes
Males have yet to be collected.

Nomenclature

 *  callipygium. Stenamma callipygium Branstetter, 2013: 63, figs. 58-60 (w.q.) GUATEMALA.

Worker
(10 measured) HL 0.69 –0.93 (0.85), HW 0.60–0.90 (0.82), FLD 0.16–0.21 (0.20), PCW 0.03–0.06 (0.05), SL 0.59–0.78 (0.75), EL 0.14–0.19 (0.18), ACL 0.55–0.66 (0.65), ML 0.93–1.23 (1.13), PrW 0.41–0.56 (0.51), PSL 0.08–0.10 (0.10), SDL 0.06–0.10 (0.10), PL 0.30–0.42 (0.38), PH 0.19–0.26 (0.24), PW 0.41–0.56 (0.51), PPL 0.20–0.27 (0.27), PPH 0.19–0.26 (0.24), PPW 0.21– 0.32 (0.28), MFL 0.71–0.98 (0.93), MTL 0.55–0.77 (0.73), CI 86–97 (96), SI 86–98 (91), REL 20–24 (21), FLI 22–27 (24), PSI 1.0–1.4 (1.0), MFI 84–92 (89), ACI1 62–68 (63), ACI2 84–94 (87).

Medium-sized species; general body color black to dark brown, with appendages brown to orange-brown; setae dark brown; mandible with 6–7 teeth, consisting of 3–4 distinct apical teeth, an indistinct basal tooth, and 2–3 inner denticles; basal third of mandible distinctly attenuated (dorsoventrally thinned), with masticatory and basal margins somewhat elongated, attenuated section bordered by an oblique carina; basal margin of mandible sinuous, but without a basal notch or distinct depression; mandible surface mostly smooth and shiny, with scattered piligerous punctae; anterior clypeal margin reduced and mostly hidden underneath the median lobe; median lobe of clypeus projecting out over mandibles, forming a well-defined, blunt apex (almost tooth-like), clypeal carinae absent, remainder of clypeus mostly smooth and shiny; posterior extension of clypeus between antennal insertions of moderate to wide width (PCW 0.03–0.06), sides subparallel; frontal lobes of moderate width (FLD 0.16–0.21, FLI 22–27), but not completely obscuring torular lobes in full-face view; head usually robust and somewhat heart-shaped (CI 86–97), with posterior margin broadly depressed medially; eye large (EL 0.14–0.19, REL20–24), oval-shaped, with 9–10 ommatidia at greatest diameter; face densely sculptured with a fan of longitudinal carinulae that extend to the posterior and lateral margins, area between eye and antennal insertion with shorter irregular rugulae, interstices near lateral margins faintly punctate; scape of moderate length (SI 86–98), just reaching posterior margin of head when laid back; scape surface mostly smooth and shiny, with scattered piligerous punctae and a few striations; flagellum with somewhat distinct 4-segmented antennal club; side and anterior half of pronotum mostly smooth and shiny, with a few scattered rugulae; remainder of promesonotal dorsum longitudinally carinate; mesopleuron and side of propodeum with scattered rugulae and faint punctae; propodeal dorsum and declivity with transverse carinae; promesonotum in profile low-domed and somewhat asymmetrical, with apex occurring anterior of midpoint and the anterior slope longer and steeper than posterior slope; metanotal grove present, somewhat shallow; propodeal spines forming small, but sharp tubercles (PSL 0.08–0.10, PSI 1.0–1.4); petiole of moderate length and form (PL/HW 0.44–0.51); petiolar node in profile somewhat small (PH/PL 0.61–0.67), gently rounded to subquadrate, and slightly angled posteriad, anterior slope distinctly longer than posterior slope; postpetiole bulging, distinctly wider than petiole (PW/PPW 0.60–0.71), and anterior gastral constriction (most noticeable in dorsal view), anterior face of node in profile long and shield-like, posterior face truncate; anterior faces of petiolar and postpetiolar nodes smooth and shiny, posterior faces with a few rugulae and punctae; ventral surface of waist segments faintly punctate; anterior constriction of gaster distinctly elongate and with elongate dorsal striae; gaster in dorsal view with shoulder-like anterolateral corners where anterior constriction begins; remainder of gaster mostly smooth and shiny, with scattered piligerous punctae; most of body dorsum with long standing pilosity; setae on scape subdecumbent to appressed, of roughly uniform length; gastral pilosity somewhat stout and mostly forming a sparse layer of suberect to subdecumbent setae; setae on legs mostly decumbent to appressed, with suberect setae on coxae and femoral venters.

Queen
(1 measured) HL 0.88, HW 0.81, FLD 0.21, PCW 0.05, SL 0.77, EL 0.25, ACL 0.68, ML 1.38, PrW 0.76, PSL 0.14, SDL 0.12, PL 0.50, PH 0.29, PW 0.21, PPL 0.27, PPH 0.29, PPW 0.35, MFL 0.98, MTL 0.80, CI 92, SI 95, REL 30, FLI 26, PSI 1.2, MFI 83, ACI1 64, ACI2 88.

Same as worker except for standard queen modifications and as follows: mesosoma almost completely carinulate, only mesopleuron mostly smooth; pronotum with transverse carinulae; pronotum with transverse carinulae that wrap around entire surface; mesoscutum and scutellum with longitudinal carinae; anterior of mesoscutum with a short narrow strip of smooth surface from which carinulae arise; gastral setae slightly more dense.

Type Material
Holotype worker. GUATEMALA: Baja Verapaz, Biotopo Quetzal, 15.21329°N, 90.21516°W ±110m, 1715m, 8 May 2009, cloud forest, beating vegetation (LLAMA, collection Go-B-02-1-02) USNM, specimen CASENT0606207. Paratypes: same data as holotype 1w, CASC, CASENT0606206]; same data but (LLA- MA, Go-B-02-1-01) 1w, MCZ, CASENT0606203]; 15.21227°N, 90.21430° ±50m, 1750m, 7 May 2008 (LLAMA, Wa-B-02-1-37) 1w, MGBPC, CASENT0604923; 15.21278°N, 90.21552°W ±10m, 1720m, 7–10 May 2009 (LLAMA, Ft-B-02-1-01) 1w, UCDC, CASENT0606227; 15.21202°N, 90.21653°W ±207m, 1735m, 8 May 2009 (LLAMA, Ba-B-02-1-07-05) 1dq, USNM, CASENT0603928; GUATEMA- LA: Baja Verapaz, Ranchito El Quetzal, 15.21508°N, 90.22003°W, 1700m, 20 Sep 2008 (R. S. Anderson, RSA2008-139) 1w, UVGC, CASENT0606095].

Etymology
The specific epithet callipygium is derived from the word callipygian which means having a well-shaped buttocks. The name is in reference to the anterior gastral constriction, which is one of the main diagnostic features of the species.

References based on Global Ant Biodiversity Informatics

 * Branstetter M.G. 2013. Revision of the Middle American clade of the ant genus Stenamma Westwood (Hymenoptera, Formicidae, Myrmicinae). ZooKeys 295: 1277
 * Longino J. T. L., and M. G. Branstetter. 2018. The truncated bell: an enigmatic but pervasive elevational diversity pattern in Middle American ants. Ecography 41: 1-12.