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This species belongs to the Middle American clade of Stenamma (see Branstetter 2012). All conent on this page modified from Branstetter (2013) unless noted otherwise.// Distribution
Southern Mexico to Nicaragua. No records from Belize or El Salvador.
Stenamma megamanni occurs from 700–2800 m, but it is most common from 1400–2000 m (there is also one dubious record from 150 m at Pico Bonito). It mainly inhabits montane wet forest environments, such as cloud forest, oak-pine forest, riparian forest, and mesophyll forest. Specimens have been collected in samples of sifted leaf litter, by baiting, by use of a Malaise trap, and by searching. Nests are known from rotting logs, under rocks, in mud and clay banks, and in dead bark. Most collections of this species have been inside closed-canopy forest, but it has been found several times nesting in clearings near cloud forest (similar to S. manni). The highest record of the species was a log nest in a clearing between lower elevation cloud forest and higher elevation pine forest.
Worker diagnosis. Integument mostly black to red-black; medium- to large-sized species (see HL, ML, PrW below); lateral apex of hypostomal bridge projecting ventrally as a subquadrate to broadly rounded lobe, visible behind base of mandible in profile view; propodeal spines tuberculate (PSL 0.10–0.15, PSI 1.0–1.2); face and mesosoma usually completely sculptured with rugoreticulae and some carinulae (rarely with sculpture reduced); eye of moderate to large size (EL 0.14–0.19, REL 15–20), oval-shaped, with 8–11 ommatidia in greatest diameter; postpetiole usually appearing smaller than petiolar node (PPH/PH 0.85–0.98); basal margin of mandible straight to slightly sinuous; anterior clypeal margin with a median emargination.
Similar species: Stenamma manni.
Worker description. (12 measured) HL 0.93–1.15 (1.07), HW 0.80–1.08 (0.98), FLD 0.22–0.29 (0.25), PCW 0.05–0.10 (0.07), SL 0.79–0.98 (0.91), EL 0.14–0.19 (0.17), ACL 0.70–0.86 (0.78), ML 1.18–1.48 (1.36), PrW 0.53–0.69 (0.63), PSL 0.10–0.15 (0.12), SDL 0.09–0.14 (0.11), PL 0.40–0.54 (0.45), PH 0.25–0.32 (0.30), PW 0.18–0.25 (0.23), PPL 0.23–0.33 (0.26), PPH 0.21–0.31 (0.26), PPW 0.23–0.30 (0.28), MFL 0.97–1.23 (1.14), MTL 0.72–0.93 (0.85), CI 86–96 (91), SI 89–100 (93), REL 15–20 (18), FLI 25–28 (26), PSI 1.0–1.2 (1.1), MFI 82–90 (86), ACI1 61–63 (62), ACI2 84–89 (86).
Medium- to large-sized species; general body color black to red-black, with appendages black or dark brown to orange-brown, becoming lighter toward extremities at joints; setae dark golden brown to golden brown; mandible with 6 teeth, 2 teeth nearest basal tooth sometimes worn and indistinct; basal margin of mandible straight to slightly sinuous, without a basal depression or notch; mandible mostly smooth, with scattered piligerous punctae and a few striations near base and on lateral surface; anterior clypeal margin with a simple median emargination; median lobe of clypeus usually with a pair of longitudinal carinulae (type population), but sometimes surface smooth, or with several irregular carinulae, area in between carinulae often depressed; apex of lobe usually with a single transverse short carinula (type population), but sometimes with several transverse carinulae/rugulae; remainder of clypeus smooth and shiny; posterior extension of clypeus between antennal insertions of moderate width (PCW 0.05–0.10), sides subparallel; frontal lobes of moderate width (FLD 0.22–0.29; FLI 25–28) not greatly obscuring torular lobes in full-face view; lateral margin of hypostomal bridge with a projecting subquadrate lobe, visible in profile view (very rarely reduced and only visible from a lateroventral view); head roughly oval-shaped to more robust, becoming strongly heart-shaped (CI 86–96), posterior margin of head with a distinct median depression (especially in larger specimens); eye moderately large (EL 0.14–0.19, REL 15–20), oval-shaped, with 8–11 ommatidia at greatest diameter; face sculpture variable, usually strongly rugoreticulate, with some carinulae along midline (type population), but sometimes sculpture more polished, with area near posterior margin of head becoming somewhat smooth; scape of moderate length (SI 89–100), reaching posterior margin of head when laid back; scape usually thick and robust, surface carinate to carinulae with piligerous punctae; flagellum with a somewhat indistinct 4-segmented antennal club; mesosoma sculpture variable, often densely rugose, with rugae wavy, almost becoming reticulate (type population), but sculpture often reduced, with promesonotum longitudinally carinulate to nearly smooth, and side of propodeum and mesopleuron more punctate; promesonotum in profile domed, and usually asymmetrical (type population), with apex shifted anterior of midpoint, but sometimes promesonotum symmetrical; metanotal groove well- demarcated, sometimes somewhat wide and with metanotum forming a small welt (type population); propodeal spines tuberculate (PSL 0.10–0.15, PSI 1.0–1.2); petiole of moderate length, usually somewhat robust (PL/HW 0.45–0.52); petiolar node in profile of moderate height (PH/PL 0.59–0.68), dorsum usually broadly rounded and pointing vertically, only rarely forming a sharp apex; postpetiole in profile usually appearing smaller than petiolar node (PPH/PH 0.85–0.98); petiole and postpetiole usually strongly punctate, with a few rugulae on dorsum and anterior face of postpetiolar node (type population), sometimes anterior faces of petiolar and petiolar nodes mostly smooth; gaster mostly smooth, with scattered piligerous punctae; most of body dorsum with relatively long standing pilosity; pilosity on gastral dorsum sparse and mostly suberect (type population), usually with some shorter subdecumbent setae, suberect setae often somewhat stout; setae on promesonotum often noticeably erect; setae on scape uniformly suberect to decumbent; setae on legs mostly decumbent to appressed, with some suberect setae on femoral venters and coxae.
Queen description. (5 measured) HL 1.01–1.12 (1.11), HW 0.92–1.03 (0.99), FLD 0.27–0.31 (0.31), PCW 0.07–0.10 (0.09), SL 0.87–0.97 (0.95), EL 0.26–0.28 (0.28), ACL 0.76–0.83 (0.83), ML 1.55–1.72 (1.71), PrW 0.93–1.04 (0.99), PSL 0.20–0.23 (0.20), SDL 0.15–0.17 (0.16), PL 0.57–0.60 (0.60), PH 0.33–0.39 (0.36), PW 0.26–0.31 (0.30), PPL 0.30–0.34 (0.34), PPH 0.32–0.39 (0.38), PPW 0.35– 0.40 (0.38), MFL 1.13–1.26 (1.26), MTL 0.86–0.96 (0.93), CI 89–92 (89), SI 93–96 (96), REL 28–29 (28), FLI 28–31 (31), PSI 1.2–1.4 (1.2), MFI 78–84 (78), ACI1 60–62 (60), ACI2 83–89 (87).
Same as worker except for standard queen modifications and as follows: pronotum with transverse rugulae; mesoscutum longitudinally costulate; scutellum rugose to rugoreticulate; propodeum rugose to rugoreticulate; postpetiolar node larger, and somewhat anteroposteriorly compressed; mesopleuron mostly smooth; setae on mesoscutum short; setae on gastral dorsum often more dense, and more strongly bilayered, with layer of decumbent setae more dense; anterior quarter of gastral dorsum often with a layer of pubescence under stouter suberect and decumbent setae; wing venation as in specimen CASENT0604840.
Male. See specimen JTLC000007293. Note the rather peculiar propodeal protuberances. I have observed these in several specimens from different sites. Many males, however, including males from the same nest, have only small sharp tubercles.
As described under S. manni, separating S. megamanni from S. manni is difficult, because of the great diversity in S. manni phenotypes across its range. At a local scale, however, separating S. megamanni from S. manni is usually easy. Stenamma megamanni is black and has a rather large eye with 8 or more ommatidia at greatest diameter. Stenamma manni in contrast is usually a dark red-brown color and has a smaller eye with 5–6 ommatidia at greatest diameter. Preliminary phylogenetic data show that specimens from the type population and several divergent populations of S. megamanni form a clade nested within the S. manni complex (Branstetter unpublished data). This result has provided evidence that S. megamanni is a good species.
Within the concept of S. megamanni described in Branstetter (2013), there is significant variation in sculpture, size and pilosity among populations. This variation is perceived to be somewhat continuous, so separate variants are not described. However, some images depicting the variation are provided in the paper. The type form appears rather robust with the promesonotum high-domed, and asymmetrical, and the sculpture very dense (CASENT0622851). The pronotal sculpture has very wavy, almost reticulate rugae. Most populations do not match the type population exactly. The closest is a collection at the locality 2km NE Macalajau in Guatemala, which was made at high elevation (2320 m) from a ground nest under a rock in a cloud forest clearing. This habit is quite different from that of the type population, which was found at lower elevation along a stream (see "biology" section above). More commonly, workers appear somewhat less robust (CASENT0621836), with less dense sculpturing. A few populations have workers with very reduced face and promesonotal sculpture, and with more erect pilosity (CASENT0606734). One aberrant high-elevation collection from Guatemala (Pinalón) has very large workers, with transverse carinulae on the pronotum (CASENT0603924).
The specifici epithet megamanni was used to draw attention to the fact that this species looks like a larger, more robust version of S. manni.
Type material. Holotype worker. MÉXICO, Chiapas: Sierra Morena, 16.16121°N, 93.60024 ±50m, 1320m, 15 May 2008, riparian mesophyll forest, nest under stone (M. G. Branstetter, collection MGB750) [USNM, specimen CASENT0622851]. Paratypes: same data as holotype [1w, CAS, CASENT0622852], [1w, EAPZ, CASENT0622853], [1w, ECOSCE, CASENT0622854], [1w, FMNH, CASENT0622855], [1w, ICN, CASENT0622856], [1w, INBio, CASENT0623361], [1w, JTLC, CASENT0623362], [1w, LACM, CASENT0623363], [1w, MGBPC, CASENT0623364], [1w, MCZ, CASENT0623365], [1w, MZSP, CASENT0623366], [1w, UCD, CASENT0623367], [1w, UNAM, CASENT0623368, [1w, UVGC, CASENT0623369], [1w, USNM, CASENT0623370]; same data but 16.16016°N, 93.60572°W ±15m, 1360m, 15 May 2008 (LLAMA, Ma-A-01-1-01) [1dq, USNM, CASENT0604840].
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.
Found most commonly in these habitats: 193 times found in cloud forest, 14 times found in mixed hardwood forest, 20 times found in 2º mesophil forest, 6 times found in oak cloud forest, 1 times found in riparian mesophyll forest, 4 times found in cloud forest stream edge, 4 times found in dry cloud forest, 5 times found in small stream in cloud forest, 13 times found in riparian mesophil for., 4 times found in mesic forest, ...
Found most commonly in these microhabitats: 144 times ex sifted leaf litter, 138 times at bait, 2 times nest under rock, 2 times nest in clay bank, 1 times ex rotten wood, 2 times nest in mud bank, 1 times nest in dead bark, 1 times nest in log, 1 times ex rock crevice near stream, 1 times nest under rocks, 1 times at bait on rotten log, ...
Collected most commonly using these methods: 131 times Baiting, 99 times MiniWinkler, 25 times search, 33 times MaxiWinkler, 6 times Berlese/Winkler, 5 times bait, 7 times Winkler, 2 times Berlese, 2 times leaf litter, 1 times Beating, 1 times blue pan trap, ...
Elevations: collected from 150 - 2800 meters, 1524 meters average
Collect Date Range: collected between 1978-06-18 and 2013-05-06