Stenamma expolitum Smith 1962

Branstetter (2013):

Stenamma expolitum is a specialist inhabitant of clay banks. It occurs from 50–1300 m elevation in mature wet forest environments. Nests are generally found in vertical clay banks along streams or cuts along trails. The biology of S. expolitum is reviewed in detail in Longino (2005) and in the overview of natural history section above. See also the "biology" section for S. alas. These two species have nearly identical behaviors with subtle modifications, which are described here. Stenamma expolitum constructs its nests with a vertical turret, rather than a horizontal one. Each nest usually has two chambers instead of one. The main chamber connects to the turret, but there is often a secondary chamber behind the turret. The queen and brood always occur in the main chamber. Colony size is probably similar to S. alas, but so far, censused colonies tend to be smaller, with around 100 individuals. In Costa Rica, I have noticed that S. expolitum can be abundant at very low elevations, whereas S. alas is more common around 300 m and higher. It also seems to be easier to find colonies of S. expolitum away from streams in trail cuts or in steep clay slopes, suggesting that the species may be more tolerant of drier substrates.

J. Longino (Ants of Costa Rica):

Stenamma expolitum occurs in mature wet forest habitats. It is a specialist inhabitant of clay banks. Colonies are most readily encountered on nearly vertical banks along stream margins, but may also occur along trail edges where they have been cut into hillsides.

This and the related species S. alas have complex nesting behavior, reported in Longino (2005). The nest entrance is a turret of pebbles recessed in an alcove. There is one main nest chamber extending back into the bank from the entrance, and a smaller secondary chamber above the first and with entrance in the alcove above and behind the turret. Colonies maintain two or three nests in active condition but only occupy one. A door pebble is used to close the entrance to the main nest chamber when army ants are present. See the Stenamma alas page for details. Images below show examples of nest entrances.

Branstetter (2013): Nicaragua to Costa Rica.

J. Longino (Ants of Costa Rica): Costa Rica: Atlantic slope from sea level to 800m.

Worker diagnosis. Integument mostly black, with legs dark brown, changing to orange-brown only at extremities and joints; medium-sized species (see HL, ML, PrW below); petiole and postpetiole almost completely smooth and shiny, with only a few faint vestigial punctae sometimes present; postpetiole in profile bulging, globular, usually appearing more voluminous than petiolar node; face almost completely smooth and shiny, except for variable number of faint carinulae and punctae; promesonotum almost completely smooth and shiny; eye relatively large (EL 0.13–0.16, REL 18–21), oval-shaped, with 7–9 ommatidia at greatest diameter; anterior margin of clypeus with median emargination; basal margin of mandible straight; propodeal spines absent (PSL 0.12–0.14, PSI 0.9).

Similar species: Stenamma atribellum, S. alas, S. expolitico.

Worker description. (10 measured) HL 0.75–0.93, HW 0.66–0.83 (0.82), FLD 0.20–0.23 (0.23), PCW 0.05–0.08 (0.06), SL 0.63–0.78 (0.76), EL 0.13–0.16 (0.16), ACL 0.63–0.74 (0.73), ML 1.02–1.26 (1.26), PrW 0.51–0.62 (0.61), PSL 0.12–0.14 (0.13), SDL 013–0.15 (0.14), PL 0.39–0.47 (0.47), PH 0.21–0.27 (0.26), PW 0.15– 0.19 (0.18), PPL 0.24–0.30 (0.27), PPH 0.20–0.25 (0.24), PPW 0.19–0.24 (0.23), MFL 0.74–0.95 (0.91), MTL 0.58–0.75 (0.73), CI 87–92 (92), SI 91–96 (92), REL 18–21 (19), FLI 27–30 (28), PSI 0.9 (0.9), MFI 85–91 (90), ACI1 60–65 (64), ACI2 92–101. Medium-sized species; general body color black to dark red-brown, with patches of dark brown on gaster; appendages mostly dark brown with joints and extremities a lighter orange-brown; setae dark golden brown; mandible usually with 6–7 teeth, consisting of 4 distinct apical teeth, a distinct basal tooth, and 1–2 inner teeth/denticles, which are usually worn and indistinct; basal margin of mandible straight, without a basal notch or depression; mandible surface mostly smooth and shiny, with scattered piligerous punctae and a few faint striae; anterior clypeal margin with median emargination; median lobe of clypeus obliquely flattened, mostly smooth and shiny, except for transverse carinula near anterior margin, remainder of clypeus mostly smooth and shiny; posterior extension of clypeus between antennal insertions somewhat wide (PCW 0.05–0.08), with sides subparallel to slightly diverging posteriad; frontal lobes of moderate width (FLD 0.20–0.23, FLI 27–30), not covering torular lobes in full-face view; head roughly oval-shaped (CI 87–92), with posterior margin flat, not de-pressed medially; eye relatively large (EL 0.13–0.16, REL 18–21), oval-shaped, with 7–9 ommatidia at greatest diameter; face completely smooth and shiny, except for variable number of very faint carinulae extending from frontal lobes to about mid-point of head, a few carinulae on gena, and scattered piligerous punctae; scape of moderate length (SI 91–96), usually reaching posterior margin of head when laid back; scape surface mostly smooth and shiny, with scattered piligerous punctae; funiculus with distinct 4-segmented antennal club; mesosoma almost completely smooth and shiny, except for transverse carinulae on propodeal dorsum, carinae along metanotal grove, and a few scattered rugulae and piligerous punctae; metanotal grove somewhat shallow and wide; propodeal dorsum in profile flat to distinctly convex; propodeal spines absent, at most forming nearly imperceptible nubs (PSL 0.12–0.14, PSI 0.9); petiole of moderate length (PL/HW 0.53–60); petiolar node in profile robust (PH/PL 0.54–0.60), wedge-shaped, with the anterior face long and sloping and the posterior face shorter and nearly vertical; node dorsum rounded, pointing vertically or slightly posteriad; petiolar node in profile robust, more globular than petiolar node, but similarly asymmetrical with long anterior face and short vertical posterior face; petiole and postpetiole mostly smooth and shining, with a few vestigial punctae; gaster smooth and shiny, with only scattered piligerous punctae; most of body dorsum with long standing pilosity; scape setae suberect to subdecumbent; setae on gastral tergites long, sparse, and uniformly suberect; setae on legs suberect to subdecumbent, with longer suberect setae on coxae and femoral venters. Queen description. (5 measured) HL 0.87–0.96 (0.90), HW 0.78–0.87 (0.81), FLD 0.24–0.27 (0.25), PCW 0.07–0.08 (0.07), SL 0.72–0.79 (0.76), EL 0.21–0.23 (0.23), ACL 0.70–0.77 (0.71), ML 1.23–1.43 (1.32), PrW 0.67–0.78 (0.74), PSL 0.11–0.15 (0.15), SDL 0.13–0.15 (0.15), PL 0.48–0.53 (0.48), PH 0.27–0.31 (0.29), PW 0.19–0.23 (0.21), PPL 0.30–0.33 (0.30), PPH 0.26–0.30 (0.29), PPW 0.26– 0.30 (0.27), MFL 0.87–1.00 (0.93), MTL 0.67–0.79 (0.74), CI 90–92 (90), SI 91–93 (93), REL 26–28 (28), FLI 30–31 (30), PSI 0.9–1.0 (1.0), MFI 86–90 (87), ACI1 60–61 (60), ACI2 94–103 (94). Same as worker except for standard queen modifications and the following: facial sculpture more developed, with distinct carinulae extending from frontal lobes to ocelli, and some carinulae on gena; pronotum with transverse striae near posterior margin; posterior third of mesoscutum with variable amount of striae/costae, orientation variable, most often longitudinal, but sometimes transverse, or obliquely angled mesad toward posterior margin; scutellum with variable number of longitudinal costae; propodeum with more distinct transverse carinae that extend across the dorsum to upper half of side; wing venation as in specimen JTLC000005582. Male. See specimen JTLC000003501.

This species belongs to the Middle American clade of Stenamma (see Branstetter 2012). All content on this page modified from Branstetter (2013) unless noted otherwise.

Stenamma expolitum Smith, 1962a PDF: 36 (w.q.) COSTA RICA. Neotropic. AntCat AntWiki HOL

Stenamma expolitum is a species of ant native to the wet forests of Costa Rica at elevations of 800 metres (2,600 ft).

Worker description. (10 measured) HL 0.75–0.93, HW 0.66–0.83 (0.82), FLD 0.20–0.23 (0.23), PCW 0.05–0.08 (0.06), SL 0.63–0.78 (0.76), EL 0.13–0.16 (0.16), ACL 0.63–0.74 (0.73), ML 1.02–1.26 (1.26), PrW 0.51–0.62 (0.61), PSL 0.12–0.14 (0.13), SDL 013–0.15 (0.14), PL 0.39–0.47 (0.47), PH 0.21–0.27 (0.26), PW 0.15–0.19 (0.18), PPL 0.24–0.30 (0.27), PPH 0.20–0.25 (0.24), PPW 0.19–0.24 (0.23), MFL 0.74–0.95 (0.91), MTL 0.58–0.75 (0.73), CI 87–92 (92), SI 91–96 (92), REL 18–21 (19), FLI 27–30 (28), PSI 0.9 (0.9), MFI 85–91 (90), ACI1 60–65 (64), ACI2 92–101. Medium-sized species; general body color black to dark red-brown, with patches of dark brown on gaster; appendages mostly dark brown with joints and extremities a lighter orange-brown; setae dark golden brown; mandible usually with 6–7 teeth, consisting of 4 distinct apical teeth, a distinct basal tooth, and 1–2 inner teeth/denticles, which are usually worn and indistinct; basal margin of mandible straight, without a basal notch or depression; mandible surface mostly smooth and shiny, with scattered piligerous punctae and a few faint striae; anterior clypeal margin with median emargination; median lobe of clypeus obliquely flattened, mostly smooth and shiny, except for transverse carinula near anterior margin, remainder of clypeus mostly smooth and shiny; posterior extension of clypeus between antennal insertions somewhat wide (PCW 0.05–0.08), with sides subparallel to slightly diverging posteriad; frontal lobes of moderate width (FLD 0.20–0.23, FLI 27–30), not covering torular lobes in full-face view; head roughly oval-shaped (CI 87–92), with posterior margin flat, not depressed medially; eye relatively large (EL 0.13–0.16, REL 18–21), oval-shaped, with 7–9 ommatidia at greatest diameter; face completely smooth and shiny, except for variable number of very faint carinulae extending from frontal lobes to about midpoint of head, a few carinulae on gena, and scattered piligerous punctae; scape of moderate length (SI 91–96), usually reaching posterior margin of head when laid back; scape surface mostly smooth and shiny, with scattered piligerous punctae; funiculus with distinct 4-segmented antennal club; mesosoma almost completely smooth and shiny, except for transverse carinulae on propodeal dorsum, carinae along metanotal grove, and a few scattered rugulae and piligerous punctae; metanotal grove somewhat shallow and wide; propodeal dorsum in profile flat to distinctly convex; propodeal spines absent, at most forming nearly imperceptible nubs (PSL 0.12–0.14, PSI 0.9); petiole of moderate length (PL/HW 0.53–60); petiolar node in profile robust (PH/PL 0.54–0.60), wedge-shaped, with the anterior face long and sloping and the posterior face shorter and nearly vertical; node dorsum rounded, pointing vertically or slightly posteriad; petiolar node in profile robust, more globular than petiolar node, but similarly asymmetrical with long anterior face and short vertical posterior face; petiole and postpetiole mostly smooth and shining, with a few vestigial punctae; gaster smooth and shiny, with only scattered piligerous punctae; most of body dorsum with long standing pilosity; scape setae suberect to subdecumbent; setae on gastral tergites long, sparse, and uniformly suberect; setae on legs suberect to subdecumbent, with longer suberect setae on coxae and femoral venters. Queen description. (5 measured) HL 0.87–0.96 (0.90), HW 0.78–0.87 (0.81), FLD 0.24–0.27 (0.25), PCW 0.07–0.08 (0.07), SL 0.72–0.79 (0.76), EL 0.21–0.23 (0.23), ACL 0.70–0.77 (0.71), ML 1.23–1.43 (1.32), PrW 0.67–0.78 (0.74), PSL 0.11–0.15 (0.15), SDL 0.13–0.15 (0.15), PL 0.48–0.53 (0.48), PH 0.27–0.31 (0.29), PW 0.19–0.23 (0.21), PPL 0.30–0.33 (0.30), PPH 0.26–0.30 (0.29), PPW 0.26–0.30 (0.27), MFL 0.87–1.00 (0.93), MTL 0.67–0.79 (0.74), CI 90–92 (90), SI 91–93 (93), REL 26–28 (28), FLI 30–31 (30), PSI 0.9–1.0 (1.0), MFI 86–90 (87), ACI1 60–61 (60), ACI2 94–103 (94). Same as worker except for standard queen modifications and the following: facial sculpture more developed, with distinct carinulae extending from frontal lobes to ocelli, and some carinulae on gena; pronotum with transverse striae near posterior margin; posterior third of mesoscutum with variable amount of striae/costae, orientation variable, most often longitudinal, but sometimes transverse, or obliquely angled mesad toward posterior margin; scutellum with variable number of longitudinal costae; propodeum with more distinct transverse carinae that extend across the dorsum to upper half of side; wing venation as in Figure 84D. Male. See Figure 84E–G.