Stenamma schmidti

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Stenamma schmidti
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Class: Insecta
Order: Hymenoptera
Family: Formicidae
Subfamily: Myrmicinae
Tribe: Stenammini
Genus: Stenamma
Species: S. schmidti
Binomial name
Stenamma schmidti
Menozzi, 1931

Stenamma schmidti casent0039766 profile 1.jpg

Stenamma schmidti casent0039766 dorsal 1.jpg

Specimen labels

Stenamma schmidti, as defined here, is a rather variable species. It inhabits tropical wet forest environments from sea level to about 2400 m, becoming most abundant in cloud forest habitats above 800 m. At some cloud forest sites, S. schmidti can be one of the most common ant species occupying the leaf litter. Despite this fact, the species is very cryptic and finding nests is an uncommon event. Most collections of S. schmidti are from Winkler or Berlese samples of sifted leaf litter or epiphyte mats. Nest collections have been made, but these are very rare for the leaf-litter dwelling variants and only slightly more common for the arboreal forms. Nests are very small, with only tens of workers, and a single egg-laying queen. Workers, when encountered, are very slow moving and freeze upon disturbance. Additional natural history notes specific to particular morphological variants are described below (Brenstetter, 2013).


Branstetter (2013) - A highly variable species. Integument mostly dark brown, red-brown, or brown; small- to medium-sized species; petiolar node in profile usually broadly rounded and distinctly angled posteriad; postpetiole in profile subspherical; propodeal spines absent to tuberculate (PSL 0.06–0.13, PSI 0.8–1.5); basal margin of mandible usually with a distinct basal notch and small accompanying tooth, but sometimes with only a small notch, or with basal margin sinuous. If basal margin of mandible with notch and tooth then: anterior clypeal margin forming 2–4 sharp to blunt teeth, with outer teeth more projecting; eye of moderate to large size (EL 0.10–0.18, REL 19–29), with 6–10 ommatidia at greatest diameter. If basal margin with small notch, but no tooth then: face completely sculptured, densely rugoreticulate; mesosoma mostly sculptured, punctate-rugulose; pilosity on first gastral tergite sparse, mostly stout and suberect, with only a few decumbent setae. If basal margin of mandible sinuous (without notch and tooth) then: anterior clypeal margin with a simple median emargination; propodeal spines absent, reduced to blunt angles where propodeal dorsum and declivity meet; eye large (EL 0.15–0.18, REL 22–27), with 8–11 ommatidia at greatest diameter; face usually completely sculptured, but sculpture never very dense, mostly carinulatepunctate; carinulae usually longitudinal, but some specimens with transverse carinulae on anterior half of head; pronotum either completely carinulate-punctate, lightly punctate, or completely smooth; carinulae when present usually transverse in orientation; some specimens noticeably long and gracile, with scape, metafemur, and petiole relatively long (SI 107–121, 86–93; PL/HW 0.58–0.63); gastral pilosity mostly sparse and suberect, with only a few decumbent to appressed setae; erect setae often stout.

The Stenamma schmidti complex is as remarkable as it is maddening, comprising an amazing radiation of forms, which together occupy more morphospace than all of the Holarctic clade Stenamma species combined. By combining many divergent forms into a single species, it has made characterizing S. schmidti rather difficult due to its large phenotypic range and many individuals, especially those with intermediate phenotypes will probably not key out easily. S. schmidti can be difficulat to separate from the closely related Stenamma nanozoi and Stenamma sandinista, as well as from the similar looking Stenamma saenzae, based only on morphology. The characters in the key and diagnosis will work for most specimens, but not all. Fortunately, geography should clarify matters, as most of the schmidti complex occurs farther south than the other species. Only S. sandinista is found in sympatry with one variant of S. schmidti. These two species both occur at Cerro Musún in Nicaragua, where they are separated by elevation, with S. schmidti occurring below about 800 m and S. sandinista occurring above 900 m.

Keys including this Species


Nicaragua to Ecuador.

Latitudinal Distribution Pattern

Latitudinal Range: 21.135° to -0.3619°.

Tropical South

Distribution based on Regional Taxon Lists

Neotropical Region: Colombia, Costa Rica (type locality), Ecuador, Nicaragua, Panama.

Distribution based on AntMaps


Distribution based on AntWeb specimens

Check data from AntWeb

Countries Occupied

Number of countries occupied by this species based on AntWiki Regional Taxon Lists. In general, fewer countries occupied indicates a narrower range, while more countries indicates a more widespread species.

Estimated Abundance

Relative abundance based on number of AntMaps records per species (this species within the purple bar). Fewer records (to the left) indicates a less abundant/encountered species while more records (to the right) indicates more abundant/encountered species.




The following information is derived from Barry Bolton's Online Catalogue of the Ants of the World.

  • schmidti. Stenamma schmidti Menozzi, 1931d: 198, fig. 6 (w.q.) COSTA RICA.
    • Type-material: syntype workers (number not stated, “several”), 1 syntype queen.
    • Type-locality: Costa Rica: Vara Blanca, 2000 m. (H. Schmidt).
    • [Note: Branstetter, 2013: 237, refers to a holotype worker; in the original description no holotype was designated.]
    • Type-depositories: DEIB, IEUB, NHMB.
    • [Stenamma schmidti Menozzi, 1931b: 267. Nomen nudum.]
    • Branstetter, 2013: 240 (m.).
    • Status as species: Borgmeier, 1937b: 232; Smith, M.R. 1962a: 35; Kempf, 1972a: 242; Bolton, 1995b: 394; Branstetter, 2013: 237 (redescription); Fernández & Serna, 2019: 800.
    • Distribution: Colombia, Costa Rica, Ecuador, Nicaragua, Panama.



Branstetter (2013) - (63 measured) HL 0.55–0.93 (0.66), HW 0.48–0.80 (0.57), FLD 0.11–0.25 (0.16), PCW 0.02–0.06 (0.04), SL 0.46–0.82 (0.55), EL 0.09–0.18 (0.12), ACL 0.47–0.75 (0.55), ML 0.68–1.21 (0.84), PrW 0.34–0.56 (0.40), PSL 0.06–0.13 (0.09), SDL 0.06–0.11 (0.09). PL 0.25–0.45 (0.31), PH 0.16–0.28 (0.19), PW 0.13–0.21 (0.15), PPL 0.13–0.27 (0.17), PPH 0.14–0.26 (0.18), PPW 0.16–0.28 (0.20), MFL 0.50–0.98 (0.59), MTL 0.41–0.76 (0.45), CI 79–94 (86), SI 85–121 (97), REL 18–29 (21), FLI 21–33 (29), PSI 0.8–1.5 (1.1), MFI 71–108 (96), ACI1 62–68 (66), ACI2 86–105 (100).

Small- to medium-sized species; general body color dark brown, to red-brown, to brown, with appendages brown to orange-brown, lighter at joints and toward extremities; setae golden; mandible with 5–7 teeth (usually 6), with basal tooth often appearing bidentate, inner teeth sometimes worn and indistinct; basal margin of mandible usually sinuous, with a distinct basal notch and accompanying small tooth (type population), but sometimes with a basal notch and no tooth, or only sinuous; mandible mostly smooth and shiny, with scattered piligerous punctae and a variable number of basal and lateral striae; anterior clypeal margin usually forming 2–4 sharp to blunt teeth (type population), but sometimes nearly flat, or with a simple median emargination; median clypeal lobe usually rather distinct, and produced slightly over anterior clypeal margin in full-face view (type population), but sometimes obliquely flattened and not produced; dorsal surface of lobe mostly smooth and shiny (type population), or with a variable number or irregular carinulae, apex of lobe with a short to long transverse carina; area in between carina and anterior clypeal margin, usually forming a distinct cavity where mandibles insert (type population); remainder of clypeal surface mostly smooth; posterior extension of clypeus between antennal insertions of narrow to moderate width (PCW 0.02–0.06; type population), with sides subparallel; frontal lobes moderate (type population) to slightly expanded (FLD 0.11–0.25; FLI 21–33), not greatly covering torular lobes in full-face view; head usually roughly oval-shaped (type population) to subcircular, with a distinct median depression in posterior margin, but head sometimes more elongate, with posterior margin flat (CI 79–94); eye of moderate to large size, sometimes relatively very large (EL 0.09–0.18, REL 18–29), oval-shaped, often bulging, with 5–11 ommatidia at greatest diameter; face sculpture highly variable, ranging from mostly smooth and shiny, to densely rugoreticulate (type population with fine longitudinal carinulae on middle of head and on gena, posterior 1/5 of head smooth); scape ranging from relatively short and somewhat thick to long and slender (SI 85– 121), not surpassing to distinctly passing posterior margin when laid back (moderate length in type population, just reaching posterior margin); scape surface with numerous piligerous punctae, but mostly shiny; flagellum with a distinct (type population) to very distinct 4-segmented antennal club; mesosomal sculpture highly variable, ranging from mostly smooth, to densely rugose-rugoreticulate (type population with promesonotum mostly smooth and shiny, at most a few longitudinal carinulae dorsally); mesopleuron and side of propodeum mostly smooth, with some faint punctae and carinulae, propodeal dorsum and declivity with light transverse carinulae; promesonotum in profile usually low-domed and roughly symmetrical; metanotal groove variable, usually well-demarcated and of moderate width and depth (type population), but sometimes deeper and better defined, with metanotum forming a small welt, or sometimes shallow and indistinct, with propodeum connecting almost continuously to promesonotum; propodeal spines absent to tuberculate (PSL 0.06–0.13, PSI 0.8–1.5; forming a sharp angle in type population); petiole in profile appearing of moderate length (type population) to somewhat elongate (PL/ML 0.48–0.63); petiolar node usually broadly rounded and pointing distinctly posteriad (type population), but sometimes appearing subquadrate and asymmetrical, with an apex occurring at anterior margin of dorsum; petiolar node similar in size to petiolar node and subspherical; petiole and postpetiole usually mostly smooth and shiny, with only a few faint punctae (type population), but sometimes mostly punctate, rugulae sometimes present on posterior half of postpetiolar node; gaster mostly smooth, with scattered piligerous punctae; most of body dorsum with standing pilosity; gastral pilosity highly variable, sometimes distinctly bilayered, with a sparse layer of stout suberect setae, and a dense layer of short, decumbent pubescence (type population), sometimes pubescence absent, leaving only stout, suberect setae and a few decumbent setae, or sometimes all setae of moderate thickness and with variable density and layering (suberect layer usually always present); setae on scape usually relatively dense, and uniformly subdecumbent to appressed; setae on legs decumbent to appressed, with some longer suberect setae on femoral venters and coxae.


Branstetter (2013) - (16 measured) HL 0.59–0.89 (0.81), HW 0.53–0.76 (0.74), FLD 0.13–0.25 (0.22), PCW 0.03–0.07 (0.06), SL 0.48–0.81 (0.65), EL 0.16–0.25 (0.21), ACL 0.49–0.73 (0.65), ML 0.79–1.30 (1.17), PrW 0.45–0.68 (0.60), PSL 0.08–0.15 (0.12), SDL 0.08–0.13 (0.12), PL 0.30–0.47 (0.44), PH 0.18–0.26 (0.24), PW 0.16–0.23 (0.20), PPL 0.15–0.26 (0.24), PPH 0.16–0.24 (0.23), PPW 0.19–0.28 (0.26), MFL 0.53–0.93 (0.77), MTL 0.43–0.71 (0.60), CI 83–94 (91), SI 84–111 (88), REL 26–34 (29), FLI 24–34 (30), PSI 1.0–1.4 (1.0), MFI 78–103 (96), ACI1 63–67 (63), ACI2 90–106 (99).

Same as worker except for standard queen modifications and as follows (only type population queen considered): pronotum with some transverse rugulae laterad; mesoscutum lightly punctate to foveolate, with a central line of smooth cuticle; scutellum with longitudinal carinulae laterad, and a central smooth patch; propodeum with transverse carinulae that wrap around entire surface; mesopleuron mostly smooth; pilosity on mesoscutum bilayered similar to gaster, with a layer of longer erect to suberect setae, and a layer of short, dense pubescence; wing venation as in Figure 155D.


  • Branstetter, M. G. 2012. Origin and diversification of the cryptic ant genus Stenamma Westwood (Hymenoptera: Formicidae), inferred from multilocus molecular data, biogeography and natural history. Systematic Entomology 37:478-496. doi:10.1111/j.1365-3113.2012.00624.x
  • Branstetter, M.G. 2013. Revision of the Middle American clade of the ant genus Stenamma Westwood (Hymenoptera, Formicidae, Myrmicinae). ZooKeys 295, 1–277. doi:10.3897/zookeys.295.4905
  • Menozzi, C. 1931d. Qualche nuova formica di Costa Rica (Hym.). Stett. Entomol. Ztg. 92: 188-202 (page 198, fig. 6 worker, queen described)

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
  • Dattilo W. et al. 2019. MEXICO ANTS: incidence and abundance along the Nearctic-Neotropical interface. Ecology
  • Fernández, F. and S. Sendoya. 2004. Lista de las hormigas neotropicales. Biota Colombiana Volume 5, Number 1.
  • Kempf, W.W. 1972. Catalago abreviado das formigas da regiao Neotropical (Hym. Formicidae) Studia Entomologica 15(1-4).
  • 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.
  • Longino J. T., and R. K. Colwell. 2011. Density compensation, species composition, and richness of ants on a neotropical elevational gradient. Ecosphere 2(3): 16pp.
  • Longino J. et al. ADMAC project. Accessed on March 24th 2017 at
  • Menozzi C. 1931. Contribuzione alla conoscenza del microgenton di Costa Rica. III. Hymenoptera - Formicidae. Bollettino del Laboratorio di Zoologia Generale e Agraria della Reale Scuola Superiore d'Agricoltura. Portici. 25: 259-274.
  • Menozzi C. 1931. Qualche nuova formica di Costa Rica (Hym.). Stettiner Entomologische Zeitung. 92: 188-202.
  • Smith M. R. 1962. A remarkable new Stenamma from Costa Rica, with pertinent facts on other Mexican and Central American species (Hymenoptera: Formicidae). Journal of the New York Entomological Society 70: 33-38.
  • Varela-Hernandez, F., M. Rocha-Ortega, W. P. Mackay, and R. W. Jones. 2016. Lista preliminar de las hormigas (Hymenoptera: Formicidae) del estado de Queretaro, Mexico. Pages 429-435 in . W. Jones., and V. Serrano-Cardenas, editors. Historia Natural de Queretaro. Universidad Autonoma de Queretaro, Mexico.
  • Weber N. A. 1943. The ants of the Imatong Mountains, Anglo-Egyptian Sudan. Bulletin of the Museum of Comparative Zoology 93: 263-389.