Extracted from: Milliron H.E., (1973). A Monograph of the Western Hemisphere Bumblebees (Hymenoptera: Apidae; Bombinae). The Entomological Society of Canada, No. 89.|
D escription. Queen. Length, 26.0 mm; width at wing bases, 11.5 mm; abdomen, 13.0 mm, width across T2, 12.0 mm; front wing length, 20.0 mm, width, 7.0 mm. Head.\ Frontal outline (excluding mouthparts) rather narrowly trapezoidal, weakly arcuate above and rounded at the temples, little higher medially than its widest dimension, the occiput narrowly but rather abruptly elevated; vertical region flat to weakly concave, weakly inclined toward the occiput and rather sparsely covered with small inconspicuous punctures; ocular half of ocellocular area somewhat dull and with only a few microscopic punctures, the ocellar half mostly smooth and polished; compound eyes distinctly more broadly rounded below than above, their inner margins subparallel for the most part; ocelli of medium size, located in a weak arc, removed from one
another by less than their diameters, the lateral ones nearly touching the supraorbital line; malar space very little longer than distance between (and including) mandibular articulations, its surface rather unevenly and weakly convex with some irregular small punctures on lower half; labrum little more than twice as wide as its greatest thickness, the lower margin nearly straight except rounded at lateral corners, the rather prominent but not sharp shelf evenly arcu≠ ate, the tubercles only moderately prominent, not distinctly conical but transversely convex, rath≠ er deeply but not sharply separated, irregularly and rather coarsely punctate; flagellum nearly If times longer than scape, FI about If times longer than nearly quadrate F2 and nearly If times longer than rectangular F3, being almost subequal to F2 and F3 combined; clypeus sloping at sides, the entire median area evenly but not strongly convex and rather densely covered with a mixture of small to medium punctures that are sparser medially below, its median height about equal to widest part near base. Legs: Mesobasitarsite subrectangular, about 3i times longer than its widest dimension and distinctly wider than longest hairs of the posterior fringe, its outer surface broadly concave longitudinally, the acute distoposterior angle extended somewhat beyond the blunt distoanterior angle, with shallow emargination between; outer surface of hind tibia (corbicula) shiny and mostly microscopically granulose (alutaceous), only weakly convex mid-longitudinally, the broadest part distinctly wider than longest hairs of the posterior fringe; metabasitarsite with posterior margin strongly arcuate at base, beyond very weakly so to nearly straight, the widest part at least twice as broad as longest hairs of the posterior fringe, the outer surface broadly evenly and shallowly concave longitudinally, the rather subacute disto≠ posterior angle projecting little beyond the blunt distoanterior one with a shallow emargination between. Pubescence: Rather short, dense, and even throughout except somewhat longer posteriorly on the scutellum, longer and looser distally and ventrally on the abdomen; meso- basitarsal posterior fringe longer along the basal half, gradually becoming shorter beyond; corbicular fringe of medium length, rather dense, most hairs straight or nearly so except distal ones arcuate; metabasitarsal posterior fringe rather short, longest along basal half, gradually becoming shorter and sparser at the distal end of segment. Color: Mesopleura above anteriad of wing bases, thoracic dorsum except for (black) interalar band of medium width and ab≠ dominal T3 a rich golden-yellow (sometimes paler), head except for a few fine intermixed yellow hairs on vertex, legs and remainder of body black; often the anterior margin of interalar band appears irregular due to invasion of yellow and often the posterior margin is noticeably invaded in the middle by a yellow patch with its anterior margin arched onto the mesonotum (scutum). Wings black with some violaceous reflections under certain lights.
Worker. Length, 20.0 mm; width at wing bases, 9.0 mm; abdomen, 10.0 mm, width across T2, 10.0 mm; front wing length, 18.0 mm, width, 6.0 mm. Disregarding difference in overall size, this caste is essentially like the queen, except more diminutive comparative relationships of the different parts; sometimes the punctation on the clypeus is weaker, and the basitarsal posterior fringes are comparatively strongr and denser than indicated under the queen; and often the shade of yellow is paler and the interalar band narrower, lacking noticeable intrusion of yellow.
Male. Length, 19.0 mm; width at wing bases, 8.0 mm; abdomen, 9.0 mm, width across T2, 8.0 mm; front wing length, 17.0 mm, width, 6.0 mm. Head: Frontal outline (excluding mouth- parts) trapezoidal, the median height little less than the widest dimension, rather evenly arched across the top; vertical region weakly sloped toward occiput, with some medium punctures; ocellar half of the ocellocular area smooth, the ocular half at most with only weak small and medium punctures near the eye; ocelli located in a weak arc, separated from one another by slightly less than their diameters, the lateral ones well on the supraorbital line; compound eyes only a little more broadly rounded below than above, the inner margins nearly parallel; malar space nearly l i times as long as the distance between (and including) mandibular articulations, its surface irregularly weakly convex, with few small obscure punctures; labrum nearly 2£ times wider than thick, the ventral margin mostly straight but rounded at the corners, its surface irregularly flattened, the callosities weak, each with few small punctures; flagellum 4 times longer than scape, FI equal to F2, both combined at most only slightly exceeding F3, the middle segments very weakly crenulate. Legs: Mesobasitarsite subrectangular, about 4 times longer than widest part which is nearly as wide as length of most longest hairs of the posterior fringe, the outer surface shallowly concave longitudinally, the distal end subtruncate with subacute
posterior angle and blunter anterior one about equally extended; shape of metabasitarsite similar to that of mesobasitarsite except wider for the most part, with its posterior margin weakly but rather evenly arcuate from near base to distal end. Pubescence: Character similar to that in the female except slightly less dense, the more prominent hairs on the head and scutellum slightly longer; mesobasitarsal posterior fringe of medium length and density, the corresponding fringe on the metabasitarsite very short, sparse, and rather even. Genitalia and seventh and eighth abdominal sterna (PI. XV). Color: Head black except for noticeable admixture of yellow on vertex and fine pallid hairs intermixed on the face; thoracic pattern like that of the female except the yellow is paler and the rather indefinite (black) interalar band is much reduced by invasion of yellow; legs black; abdomen black except T3 and at least the basal half of T4 yellow. Wings black but somewhat less intensively so as in the female.
Comments. Aside from what has already been indicated in the redescription, little more need be said about the structural or chromatic variability in this taxon. The interalar band varies in that it is somewhat wider on certain specimens and has better defined margins; this is particularly true of the female. The nests of this humid tropical species are sometimes exceedingly populous, ranking among the largest yet known.