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Species: Stenamma huachucanum   Smith, 1957 

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Taxonomic History (provided by Barry Bolton, 2021)

Stenamma huachucanum Smith, 1957b PDF: 153, pl. 2, fig. 8 (w.) U.S.A. Nearctic. AntCat AntWiki HOL


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.

// Distribution


  Geographic regions (According to curated Geolocale/Taxon lists):
    Americas: Mexico, United States
  Biogeographic regions (According to curated Bioregion/Taxon lists):
    Nearctic, Neotropical

Distribution Notes:

Southwestern USA (Arizona, New Mexico, Texas) to southern Mexico (Oaxaca).


Stenamma huachucanum is a cryptic leaf litter ant known mostly from Winkler or Berlese samples of sifted leaf litter. As defined here, the species is widely distributed, occupying both relatively dry, seasonal habitats (e.g. tropical deciduous forest with juniper, oak-pine-juniper woodland, oak woodland, oak-pine-douglas fir forest) and tropical wet forest habitats (e.g. mesophyll forest, cloud forest, oak-pine forest). Collections have been made from 1000–2900 m, but the species is most common between 1600–2500 m. In seasonal habitats, workers have been found underneath rocks, in addition to the leaf litter.


Worker diagnosis. Note this species is variable and difficult to characterize globally. See comments section below, discussing population variants. Integument mostly dark brown to brown; small-sized species (see HL, ML, PrW below); basal margin of mandible sinuous, with a distinct basal depression, but no tooth; anterior clypeal margin undulating, forming 2–4 blunt teeth; eye of moderate size (EL 0.07–0.12, REL 14–21), oval-shaped, with 4–8 (usually 5–6) ommatidia at greatest diameter; propodeal spines tuberculate to short (PSL 0.06–0.11, PSI 1.0–1.4); face usually completely sculptured, with carinulae, rugoreticulae and punctae, but some populations with posterior ¼ or less of head smooth and shiny; pronotal sculpture variable, often with some carinulae and punctae, but some populations completely smooth; remainder of mesosoma sculptured, with punctae, carinulae and/or rugulae; propodeal lobe in profile usually isolated from propodeal spine and with angulate corners, but some populations with lobe appearing broadly rounded and forming a smooth connection with propodeal spine; geography is useful in species determination.

Similar species: Stenamma connectum, S. crypticum.

     Worker description. (28 measured; paratype CASENT0105666 in parentheses) HL 0.52–0.72 (0.72), HW 0.46–0.64 (0.62), FLD 0.11–0.17 (0.17), PCW 0.03– 0.05 (0.03), SL 0.43–0.55 (0.55), EL 0.07–0.12 (0.10), ACL 0.43–0.52 (0.52), ML 0.66–0.85 (0.85), PrW 0.33–0.41 (0.41), PSL 0.06–0.11 (0.09), SDL 0.05–0.09 (0.08), PL 0.23–0.35 (0.32), PH 0.15–0.21 (0.21), PW 0.11–0.16 (0.15), PPL 0.13– 0.20 (0.17), PPH 0.14–0.19 (0.18), PPW 0.15–0.20 (0.19), MFL 0.44–0.59 (0.59), MTL 0.37–0.48 (0.48), CI 83–91 (86), SI 81–94 (89), REL 14–21 (15), FLI 23–29 (27), PSI 1.0–1.4 (1.1), MFI 101–124 (105), ACI1 67–71 (68), ACI2 92–103 (95).
     Small-sized species; general body dark brown to brown (type population), with appendages brown or orange-brown to yellow-brown, usually lighter at joints and toward extremities; setae golden brown; mandible with 6–7 teeth, 2–3 teeth near basal tooth sometimes worn and indistinct; basal margin of mandible sinuous, with a distinct basal depression, but no tooth; mandible mostly smooth and shiny, with some scattered piligerous punctae, and some striations near base and on lateral surface; anterior clypeal margin undulating, forming 2–4 sharp to blunt teeth (4 sharp teeth in type population); median lobe of clypeus with a pair of longitudinal carinulae that diverge toward anterior margin, apex with a short transverse carinula, area in between median lobe and anterior clypeal margin forming a shallow concavity; remaining surface of clypeus mostly smooth; posterior extension of clypeus between antennal insertions somewhat narrow to moderate width (PCW 0.03–0.05), with sides subparallel; frontal lobes of moderate width (FLD 0.11–0.17, FLI 23–29), not greatly obscuring torular lobes in full-face view; head subrectangular to roughly oval-shaped (CI 83– 92), posterior margin slightly depressed medially; eye of moderate size (EL 0.07–0.12, REL 14–21), oval-shaped, with 4–8 (usually 5–6) ommatidia at greatest diameter; face sculpture variable, usually completely sculptured, with light rugoreticulae, longitudinal carinulae, and/or punctae, but sometimes sculpture reduced, with posterior 1/4 or less of head becoming smooth and shiny; scape of short to moderate length (SI 81–94), usually not quite reaching posterior margin of head when laid back; scape surface mostly smooth to somewhat rough (type population), with variable density of piligerous punctae; flagellum with a distinct 4-segmented antennal club; pronotal sculpture highly variable, often with some longitudinal carinulae/rugulae and faint punctae (type population), but some populations completely smooth; remainder of mesosoma completely sculptured with punctae and a variable amount of rugulae/carinulae; promesonotum usually low-domed, and asymmetrical, with the anterior face longer and steeper than posterior face (type population), but some populations with promesonotum distinctly domed, and roughly symmetrical; metantoal groove present and distinct, of average width and depth; propodeal lobe in profile usually isolated from propodeal spine and with angulate corners, but some populations with lobe appearing broadly rounded and forming a smooth connection with propodeal spine; propodeal spines tuberculate to short (PSL 0.06–0.11, PSI 1.0–1.4); petiole length and shape variable, often short and stocky, with a somewhat large node that points vertically, and a sinuous venter (type population), but sometimes more elongate, with node smaller and pointing distinctly posteriad, or sometimes anteroposteriorly compressed, making it very narrow (PL/HW 0.46–0.59); postpetiole usually forming a small node, similar in size or smaller than petiolar node (type population) (PPH/PL 0.79–0.97); petiole and postpetiole usually mostly punctate, with only anterior faces of nodes smooth (type population), but some populations with punctae reduced and nodes mostly smooth; gaster usually completely smooth, but some populations with first sternite and tergite lightly to strongly punctate (variable in type population); most of body dorsum with relatively short standing pilosity; gastral pilosity distinctly to indistinctly bilayered, with a layer of longer suberect to subdecumbent setae, and a layer of decumbent setae, density of setae variable, usually relatively dense (type population); setae on scape decumbent to appressed; setae on legs decumbent to appressed with longer setae on femoral venters and coxae.
     Queen description. (8 measured) HL 0.55–0.71 (0.68), HW 0.50–0.65 (0.58) FLD 0.13–0.18 (0.16), PCW 0.03–0.05 (0.04), SL 0.43–0.56 (0.49), EL 0.15–0.18 (0.15), ACL 0.42–0.52 (0.49), ML 0.78–0.98 (0.85), PrW 0.43–0.59 (0.44), PSL 0.09–0.16 (0.12), SDL 0.06–0.10 (0.09), PL 0.29–0.38 (0.34), PH 0.16–0.23 (0.22), PW 0.13–0.18 (0.16), PPL 0.13–0.20 (0.18), PPH 0.15–0.21 (0.20), PPW 0.16– 0.23 (0.21), MFL 0.46–0.60 (0.51), MTL 0.41–0.52 (0.45), CI 86–94 (86), SI 82–87 (85), REL 25–31 (25), FLI 23–28 (27), PSI 1.3–1.8 (1.3), MFI 105–114 (113), ACI1 66–71 (68), ACI2 92–100 (99).
     Same as worker except for standard queen modifications and as follows (comparison with queens from near type locality only): pronotum with transverse carinulae/rugulae; mesoscutum longitudinally carinulate, with a small patch of smooth cuticle anteromesad; scutellum smooth along midline, with longitudinal rugulae mesad; anepisternum partly smooth, remainder carinulate; katepisternum mostly smooth; propodeum with transverse carinulae that wrap around propodeum; propodeal spines longer than worker; gastral pilosity denser; wing venation as in specimen CASENT0600094.
     Male. Unknown.


Stenamma huachucanum forms a difficult complex composed of many divergent allopatric populations. The complex probably includes several good biological species, but I have chosen to lump most forms into a single entity, because there is no clear evidence of sympatry among forms, and some specimens appear to have intermediate phenotypes that connect distinct forms. The exceptions to this lumping approach are the similar species S. connectum and S. crypticum. These species are morphologically similar to S. huachucanum, but molecular phylogenetic results provide strong evidence that they represent separate lineages (Branstetter unpublished data).

There are some key morphological differences separating populations of S. huachucanum from S. connectum and S. crypticum, but considering all of the variation among populations, the easiest way to identify species is with geography. Stenamma huachucanum occurs from the southwestern U.S.A to Oaxaca, where it is found only in the drier, interior of the state. In eastern Mexico, the species is found from Tamaulipas to Puebla, with no records from Veracruz. Stenamma connectum is found in Veracruz, Mexico and on the wetter, Caribbean slope of Oaxaca. Stenamma crypticum occurs mainly from Chiapas, Mexico to Nicaragua. However, as noted under both S. crypticum and S. connectum, a few putative S. crypticum specimens are known from one sample taken in Veracruz, nearly in sympatry with S. connectum. If confirmed, this latter case is the only evidence of sympatry among any of these similar-looking species.

Within the S. huachucanum complex there is considerable variation among populations. To help in the identification of S. huachucanum, and to aid future taxonomic efforts, Branstetter (2013) describes several S. huachucanum variants (below). One observation about variation within the complex is that specimens from western and central Mexico, where it is drier, tend to look more like the type population. Specimens from the eastern slope, where it is wetter, become smoother and more aberrant, in general. The most problematic areas are in central Mexico where it transitions from wet to dry. At these localities specimens with intermediate features are found. This is one of the main reasons why Branstetter (2013) lumps together variants that seem very different from one another.

The main features of the type form of S. huachucanum (CASENT010566) are indicated in the species description of Branstetter (2013). The key characters for the type form are sculpturing and the shape of the petiole. The head is completely sculptured and mostly rugoreticulate-punctate, with some longitudinal carinulae along the midline. The pronotum is lightly carinulate-punctate (longitudinal orientation), with small smooth patches on the dorsum. One characteristic unseen by Smith (1957) or Snelling (1973) is that some specimens of S. huachucanum from the southwestern U.S.A. have the first gastral tergite and sternite punctate. Branstetter (2013) treats this as intraspecific variation as no other characters within these specimens vary significantly. The petiole of the type form has a distinctive shape, shared by several of the variants. It is rather short in length, but with a tall vertically projecting node that is roughly symmetrical in profile. Also, the venter of the petiole usually has a distinct sinuosity that often includes a small anteroventral process. A peculiarity I have noticed among worker specimens from Arizona is that they vary significantly in size, with some appearing to have allometrically enlarged heads.

Variant 1 (CASENT0600124) was collected in Sinaloa, Mexico. It is very similar to the type form except as follows: promesonotum more domed; pronotal dorsum strongly carinulate, without punctae.

Variant 2 (CASENT0605749) was collected from Volcán de Tequila in Jalisco, Mexico. It is similar to the type form except as follows: pronotum mostly smooth; petiolar node in profile broader; petiolar venter in profile straight, not sinuous.

Variant 3 (CASENT0605412) is from the drier portion of Oaxaca (Asunción Nochixtlan). It varies from the type form as follows: promesonotum distinctly domed and mostly smooth; petiolar node broader, more robust; face sculpture reduced, with posterior margin becoming smooth, and rugoreticulae less visible. Similar-looking specimens also occur in Mexico state (Temascaltepec).

Variant 4 (CASENT0604596) is from another site in Oaxaca (10.6km N Jct 190/135). It varies from the type as follows: promesonotum in profile low-domed and appearing very long, with the anterior face sloping gently into the metanotal groove; pronotum with many longitudinal carinulae around humeri, and a few on dorsum; gastral pilosity longer.

Variant 5 (CASENT0605616) is a wet forest version of S. huachucanum. It occurs at several sites on the eastern slope of the mountains in Querétaro. There are similar looking specimens from San Luis Potosí and Hidalgo states. It differs from the type population as follows: overal body size smaller; face sculpture reduced, with posterior ¼ or less of head smooth, remaining sculpture consisting of fine punctae, carinulae, and rugoreticulae; pronotum and dorsum of mesonotum smooth; promesonotum in profile variable, sometimes more flat, with posterior face merging smoothly into metanotum, sometimes more distinctly domed; petiolar node in profile narrow, appearing anteroposteriorly compressed. The specimens with a more domed promesonotum appear intermediate with variant 6.

Variant 6 (CASENT0605647) is another wet forest version of S. huachucanum. It occurs throughout the El Cielo reserve in Tamaulipas, Mexico, and differs from variant 5 as follows: head more robust, slightly broader, with posterior margin distinctly depressed medially; promesonotum domed, only slightly asymmetrical; propodeal spines forming well-developed, blunt tubercles; outline of propodeum in profile sinuous, with propodeal spine and lobe smoothly connected; petiole appearing elongate; petiolar node small, with a rounded dorsum that points distinctly posteriad.

Taxonomic Notes:

Stenamma huachucanum Smith, M. R. 1957: 153, pl 2, fig 8. Holotype worker: USA, Arizona, [Cochise Co.]: Head of Carr Canyon, Huachuca Mts., [ca. 31.432°N, 110.284°W], 8000 ft. [2440 m], 24 July 1950 (W. S. Creighton) (USNM) [examined]. Snelling, 1973: 34, figs 44, 45, 61, notes on worker. Branstetter, 2009: worker images. Branstetter, 2012: phylogeny, worker images. Branstetter, 2013: worker, queen descriptions and images.

Stenamma mgb38 [variant 5 here] Branstetter, 2012: phylogeny.


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. 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.

Specimen Habitat Summary

Found most commonly in these habitats: 7 times found in mesophyll forest, 7 times found in oak-pine forest, 2 times found in Liquidambar forest, 2 times found in disturbed mesophyll forest, 7 times found in cloud forest, 6 times found in 2nd mesophyl forest, 2 times found in pine-oak forest, 2 times found in forest, 1 times found in trop. decid. forest with Juniper, ravine, 3 times found in oak forest, ...

Found most commonly in these microhabitats: 36 times ex sifted leaf litter, 6 times ex sifted litter, 3 times under stone, 1 times ex sifted leaf litter at stream edge, 3 times ex forest litter, 3 times sifted litter (leaf mold, rotten wood), 3 times at bait, 1 times ex sifted leaf and log litter, 1 times Under rock on sunny, open slope., 1 times ex sifted leaf litter and fungi, 1 times under stone in partial shade, ...

Collected most commonly using these methods: 13 times maxiWinkler, 27 times Berlese, 11 times Winkler, 6 times search, 3 times bait, 2 times hand collecting, 1 times pitfall trap, 1 times sift, 1 times sugar bait.

Elevations: collected from 760 - 2900 meters, 1760 meters average

Collect Date Range: collected between 1950-07-24 and 2019-06-15

Type specimens:

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