Stenamma huachucanum

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. (Branstetter, 2013).

Identification
Key to Middle America Stenamma

Branstetter (2013) - Note this species is variable and difficult to characterize globally (and it is likely the species as defined here is a group of closely related species). Variants are explained more in detail in Branstetter (2013). 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, Stenamma crypticum.

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.

Within the S. huachucanum complex there is considerable variation among populations. A key note regarding variation within the species 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.

Distribution
Southwestern United States (Arizona, New Mexico and Texas) to southern Mexico (Oaxaca).

Distribution based on Regional Taxon Lists
Nearctic Region: United States. Neotropical Region: Mexico.

Nomenclature

 *  huachucanum. Stenamma huachucanum Smith, M.R. 1957b: 153, pl. 2, fig. 8 (w.) U.S.A. Branstetter, 2013: 127 (q.).

Worker
Branstetter (2013) - (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
Branstetter (2013) - (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.

Type Material
Head of Carr Canyon, 8,000 feet, Huachuca Mountains, Arizona. The holotype and eight paratype workers are in the collection of the U. S. National Museum under No. 62393. The remaining paratypes are in the collection of W. S. Creighton.

Branstetter (2013) - 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].

Etymology
Toponym. Named for the Huachuca Mountains.