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Species: Stenamma vexator   Branstetter, 2013 

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Taxonomic History (provided by Barry Bolton, 2020)

Stenamma vexator Branstetter, 2013 PDF: 263, figs. 165-168 (w.q.) MEXICO. AntCat AntWiki


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
  Biogeographic regions (According to curated Bioregion/Taxon lists):
    Nearctic, Neotropical

Distribution Notes:

Mexico (Atlatic slope).


This species is known only from Winkler and Berlese samples of sifted leaf litter. It occurs from approximately 1000–2000 m elevation and inhabits a variety of montane mesic forest environments (e.g. cloud forest, wet oak forest, oak-pine forest, tropical subevergreen forest, Liquidambar forest).


Worker diagnosis. Integument mostly black or dark brown to red-brown; small- to medium-sized species (see HL, ML, PrW below); anterior clypeal margin undulating, forming 2–4 blunt teeth; basal margin of mandible usually sinuous, with a slight basal depression, but without a tooth; face completely sculptured, mostly rugoreticulate; pilosity on gastral dorsum predominately suberect and relatively sparse; eye of moderate size (EL 0.10–0.15, REL 18–22), oval-shaped, with 5–8 ommatidia at greatest diameter; propodeal spines tuberculate to short (PSL 0.08–0.16, PSI 1.1–1.8), often robust; petiole in profile often distinctive, appearing somewhat elongate, with node broadly rounded and pointed posteriad, venter under node with a small concavity.

Similar species: Stenamma crypticum, S. huachucanum, S. stictosomum.

     Worker description. (29 measured) HL 0.62–0.78 (0.65), HW 0.55–0.71 (0.58), FLD 0.15–0.20 (0.16), PCW 0.04–0.06 (0.04), SL 0.50–0.67 (0.55), EL 0.10–0.15 (0.12), ACL 0.48–0.60 (0.50), ML 0.77–1.02 (0.85), PrW 0.39–0.49 (0.43), PSL 0.08–0.16, SDL 0.07–0.10 (0.09), PL 0.31–0.40 (0.34), PH 0.17–0.23 (0.19), PW 0.14–0.19 (0.15), PPL 0.15–0.22 (0.20), PPH 0.16–0.21 (0.17), PPW 0.17–0.22 (0.19), MFL 0.53–0.76 (0.60), MTL 0.45–0.62 (0.48), CI 89–96 (89), SI 85–98 (94), REL 18–22 (21), FLI 25–29 (28), PSI 1.1–1.8 (1.6), PI 53–59 (59), MFI 93– 107 (97), ACI1 65–71 (68), ACI2 87–98 (92).
     Small- to medium-sized species; general body color black, or dark brown to red-brown (type population), with appendages brown to orange-brown or yellow-brown, lighter in joints and toward extremities; setae golden brown; mandible with 6 teeth, 2 teeth nearest basal tooth sometimes more worn and less distinct, basal tooth often well-defined, projecting; basal margin of mandible usually sinuous, with a slight basal depression (type population), but without a tooth, some populations with basal margin almost straight; mandible mostly smooth, with scattered piligerous punctae, and some striations near base and along lateral surface; median lobe of clypeus with a pair of faint longitudinal carinulae that diverge anteriorly, apex of lobe with a short transverse carinula, remainder of clypeus mostly smooth; area in between median lobe and anterior clypeal margin forming a distinct concavity where mandibles insert; posterior extension of clypeus between frontal lobes of moderate width (PCW 0.04–0.06), with sides subparallel; frontal lobes of moderate width (FLD 0.15–0.20, FLI 25–29), not greatly covering torular lobes in full-face view; head roughly oval-shaped (CI 89–96), with posterior margin flat to slightly depressed medially; eye of moderate size (EL 0.10–0.15, REL 18–22), oval-shaped, with 5–8 ommatidia at greatest diameter; face usually strongly sculptured, mostly rugoreticulate, with some longitudinal rugae along midline (type population), some populations with sculpture somewhat polished and reticulate less distinct; scape of moderate length (SI 85–98), just reaching posterior margin of head when laid back; surface of scape mostly smooth, with scattered piligerous punctae; flagellum with distinct 4-segmented antennal club; mesosoma usually completely sculptured (type population), but some populations shinier overall and with pronotum mostly smooth and shiny; pronotal dorsum longitudinally rugose, with rugae dense to somewhat sparse and irregular, rugae usually becoming punctae and reticulae on dorsum of mesonotum; side of pronotum mostly punctate or rugose, often with a small to large patch of smooth cuticle on ventral half; mesopleuron and side of propodeum rugulose-punctate; propodeal dorsum with rugoreticulae near anterior margin, changing to transverse carinulae near posterior margin; promesonotum in profile low-domed, slightly asymmetrical, with apex posterior of midpoint, anterior declivity of pronotum sometimes forming a sharp transition with dorsum, sculpture on declivity punctate, contrasting with rugose dorsum; metanotal groove usually well-demarcated, of moderate depth and width; propodeal spines tuberculate to short (PSL 0.08–0.16, PSI 1.1–1.8), often somewhat robust (type population); petiole in profile often distinctive, appearing somewhat elongate (PL/HW 0.53–0.56), with node broadly rounded and pointed posteriad, venter under node often with a small concavity; peduncle sometimes noticeably slender, thickening toward node; postpetiole in profile subspherical, similar in size to petiolar node (PPH/PH 0.85–0.91); anterior face of petiolar and postpetiolar nodes smooth, remainder of waist mostly punctate; gaster mostly smooth and shiny, with scattered piligerous punctae; pilosity on head, short and bilayered, with some longer suberect setae, and many shorter decumbent setae, remainder of body dorsum with longer suberect setae; pilosity on gastral dorsum predominately suberect and relatively sparse; setae on scape mostly subdecumbent; setae on legs mostly subdecumbent to appressed, with some longer suberect setae on femoral venters and coxae.
     Queen description. (11 measured) HL 0.66–0.77 (0.66), HW 0.60–0.70 (0.60), FLD 0.17–0.20 (0.18), PCW 0.05–0.07 (0.05), SL 0.53–0.64 (0.53), EL 0.18–0.20 (0.18), ACL 0.50–0.60 (0.51), ML 0.94–1.13 (0.94), PrW 0.53–0.64 (0.54), PSL 0.14–0.17 (0.15), SDL 0.09–0.12 (0.09), PL 0.37–0.44 (0.38), PH 0.19–0.23 (0.20), PW 0.16–0.19 (0.17), PPL 0.18–0.22 (0.20), PPH 0.18–0.23 (0.19), PPW 0.20– 0.24 (0.20), MFL 0.59–0.75 (0.59), MTL 0.49–0.61 (0.51), CI 90–95 (92), SI 84–95 (87), REL 28–30 (30), FLI 26–30 (29), PSI 1.3–1.8 (1.6), MFI 90–104 (102), ACI1 65–68 (68), ACI2 88–98 (96).
     Same as worker except for standard queen modifications and as follows: pronotum with transverse rugae and rugoreticulae on lateral surface, changing to carinulae and punctae mesad; mesoscutum densely longitudinally rugose; scutellum rugose to rugoreticulate, sometimes with a smooth patch mesad; side of propodeum rugulose, with faint punctae, dorsum with transverse carinulae; wing venation as in specimen CASENT0126490.
     Male. Unknown.


Stenamma vexator is not a particularly distinctive species, but it should be separable from similar species by the diagnostic character states given above and in the key. It bears the most resemblance to S. huachucanum, which occurs in sympatry with S. vexator at several sites. Stenamma vexator is usually larger than S. huachucanum and has a longer, more distinctive petiole. Molecular phylogenetic data tentatively show that S. vexator is sister to the diversum species group, which includes S. diversum and S. tico (Branstetter 2012, unpublished data).

Several aberrant populations are worth separating out as variants of S. vexator. Variant 1 (CASENT0604610) occurs at several sites in Puebla, Mexico. It has the propodeal spines tuberculate, the basal margin of the mandible nearly straight, and the clypeal teeth reduced to blunt nubs. Variant 2 (CASENT0605506) is known from a few collections taken at high elevation between Oaxaca and Valle Nacional, in Oaxaca, Mexico. It is larger, darker, and has reduced sculpturing, with the pronotum mostly smooth and shiny. It also has the propodeal spines tuberculate, and the petiolar node pointing more vertically. Intermediate specimens between this variant and the holotype form of S. vexator have not been observed, so it is possible that this high elevation variant represents a distinct species. Variant 3 (CASENT0604721) is known from the locality Coapilla in Chiapas, Mexico. These specimens are black, have reduced sculpture, and have the propodeal spines almost absent. The petiolar node is also sharper and pointing more vertically. Placement of variant 3 within S. vexator is uncertain and needs to be confirmed with molecular data.

Taxonomic Notes:

Type material. Holotype worker. MÉXICO, Veracruz: 1.2mi [1.9km] S Huatusco, [ca. 19.193°N, 96.956°W], 1344m, 2-5 Aug 1969, cloud forest, [Berlese sample of sifted leaf litter] (S. & J. Peck, collection ANTC18239) [USNM, specimen CASENT0126485]. Paratypes: same data as holotype [1dq, 1w, CAS, CASENT0126500, CASENT0126495], [1dq, 1w, FMNH, CASENT126502, CASENT0126499], [1dq, 1w, INBio, CASENT0126503, CASENT0126506], [1w, JTLC, CASENT0126507], [1dq, 1w, LACM, CASENT0126487, CASENT0126486], [1dq, 1w, MGBPC, CASENT0126511, CASENT0126512], [1dq, 1w, MCZ, CASENT0126523, CASENT0126496], [1w, MZSP, CASENT0126517], [1dq, 1w, UCD, CASENT0126520, CASENT0126501], [1dq, 1w, UNAM, CASENT0126513, CASENT0126498], [1dq, 1w, USNM, CASENT0126490, CASENT0126492].

Specimen Habitat Summary

Found most commonly in these habitats: 123 times found in cloud forest, 8 times found in montane wet forest, 1 times found in forest, 1 times found in 2nd mesophyl forest, 1 times found in oak forest, 1 times found in oak forest litter, 1 times found in oak-pine forest, 1 times found in trans/cloud forest, 1 times found in moist oak forest, 1 times found in Platanus, tropical subevergreen forest near stream, ...

Found most commonly in these microhabitats: 115 times ex sifted leaf litter, 22 times at bait, 1 times ex sifted litter, 1 times ex sifted leaf litter and fungi, 1 times leaf litter Berlese, 1 times forest litter, 1 times ex leaf litter and flood debris near stream.

Collected most commonly using these methods: 98 times miniWinkler, 18 times Berlese, 22 times baiting, 3 times maxiWinkler, 1 times Winkler, 1 times Berlese/Winkler.

Elevations: collected from 1070 - 2040 meters, 1490 meters average

Collect Date Range: collected between 1946-04-18 and 2019-06-13

Type specimens: Holotype Stenamma vexator: casent0126485; Paratype Stenamma vexator: casent0126486, casent0126487, casent0126490, casent0126492, casent0126495, casent0126496, casent0126498, casent0126499, casent0126500, casent0126501, casent0126502, casent0126503, casent0126506, casent0126507, casent0126511, casent0126512, casent0126513, casent0126517, casent0126520, casent0126523

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