Extracted from: Milliron H.E., (1973). A Monograph of the Western Hemisphere Bumblebees (Hymenoptera: Apidae; Bombinae). The Entomological Society of Canada, No. 89.|
Description. Queen. Length, 25.0 mm; width at wing bases, 11.0 mm; abdomen, 13.0 mm, across T2, 11.5 mm; front wing length, 20.0 mm, width, 7.0 mm. Head: Frontal outline (excluding mouthparts) mostly round trapezoidal, greatest width through compound eyes subequal to height, rather evenly rounded above; vertical region with limited smooth concavities laterad of ocelli which are situated in weak arc just below supraorbital line, separated from one another by little less than widest diameter of median ocellus, the interocellar line somewhat greater than ocelF ocular line; ocular half of ocellocular area microscopically punctate with few deeper punctures behind; compound eyes with inner margins nearly parallel except above, each eye more broadly rounded below, about 21 times higher than greatest width; clypeus basally wider than median height, disc evenly but not strongly convex, for the most part covered with medium punctures; ventral margin of labrum broadly arcuate, the tubercles irregularly rounded below and without strong mesal summits, coarsely irregularly punctate and not very widely separated; malar space somewhat shorter than distance between (and including) mandibular articulations, weakly con vex, smooth and bearing some microscopic hairs; flagellum If times longer than scape, FI subequal to F2 plus 3, F2 distinctly shorter than F3. Legs: Mesobasitarsite subrectangular, about 3 times longer than its greatest width, its outer surface rather strongly concave mid- longitudinally, the rounded distoanterior angle in recess of acute distoposterior angle and with distinct emargination between; outer hind tibial surface for the most part smooth and polished, mid- longitudinally convex to about distal one-quarter; metabasitarsite with outer surface broadly and strongly concave mid-longitudinally, covered with fine suberect pubescence, nearly 3 times longer than widest dimension, distal end (and angles) similar to that of mesobasitarsite, posterior margin strongly arcuate near base, progressively evenly and more weakly so to distal end. Pubescence: Rather short and even except somewhat longer on scutellum and antepenultimate abdominal tergum, dense; corbicular fringe moderately dense, hairs weakly arcuate except distal ones more strongly so, longest ones subequal to widest measurement of tibia; metabasi-
tarsal posterior fringe rather short, longer arcuate hairs basally, gradually diminishing in length distally, sparser and inconspicuous on distal third. Color: Head black with few pale hairs intermixed on vertex, becoming burnt sienna on most of occiput; thoracic disc russet brown (often lighter approaching shades of yellow blending to brownish yellow on pronotum and most of scutellum), sides of thorax below wing bases black except for few intermixed pale hairs on metapleural region; legs black; abdominal Tl-3 mostly black, with some pubescence covering anterolateral areas of T1 burnt sienna and some blackish with pale tips, a scant amount mid- basally on T2 tawny yellowish, elsewhere on T2—3 a few scattered rufescent hairs especially laterally and distally, T4-6 bright rufous, the abdominal venter rufescent with brownish tinge to pile on mid- and basal sterna. Wings deeply infumated, with some violaceous reflection under certain light, paler in the discal area.
Worker. Except for generally smaler size, taxonomic characters in this caste are relatively similar to those detailed for the queen. Color: Head black; thorax above (usually) more of a tawny yellow; abdominal Tl-3 largely black, T4-6 (usually) paler rufescent. Wings little lighter and more uniformly infumated, (usually) with some violaceous reflection.
Male. Length, 16.0 mm; width at wing bases, 8.0 mm; abdomen, 8.0 mm, width across T2, 7.5 mm; front wing length, 14.0 mm, width, 4.5 mm. Head: Frontal outline (excluding mouthparts) suggestive of well rounded trapezoid, especially rounded behind eyes, less so on the vertical region, its widest dimension about equal to median height; vertical region only weakly concave laterad of ocelli; interocellar line about equal to ocellocular line; ocular half of ocellocular area with microscopic punctation, the ocellar half smooth and polished; labrum twice as broad as thick, its outer surface mostly punctate, the callosities weak; malar space slightly shorter than distance between (and including) mandibular articulations, weakly convex, mostly microscopically punctate; flagellum 4 times longer than scape, FI and 2 about equal in length and together slightly longer than F3. Legs: Mesobasitarsite rectangular, about 4 times longer than widest dimension, its outer surface strongly concave longitudinally, the end emarginate between subacute distal angles; hind tibial outer surface longitudinally convex, well covered with rather short hairs, the posterior marginal fringe short and not markedly differentiated; metabasitarsite nearly 31 times longer than greatest width, subrectangular, its outer surface for the most part mid-longitudinally concave, covered with fine suberect hairs, the posterior fringe short, even and moderately dense, distal end distinctly emarginate between subacute disto posterior and more rounded distoanterior angles. Pubescence: In respect to length, density and evenness similar to that of the female. Genitalia, seventh and eighth abdominal sterna (PI. XIV). Color: Head black intermixed with cinereous pile on face and lower genal region and burnt
sienna hairs with paler tips on the occiput; thoracic dorsum pale brownish yellow (amber colored), pleura mostly blackish mixed with some pale (tawny) hairs above, becoming tawny below and on metapleura; legs mostly black intermixed with some pale hairs on femora, largely pallid on trochanters and coxae; abdominal T1 (largely), at least basal middle of T2, and some hairs along base of T3 tawny yellowish, otherwise T2-3 black, except distally on T3 (some) and T4 (except few blackish hairs intermixed basally) and all of T5-7 rufescent, the abdominal venter mostly pale rufescent. Wings as in the worker.
Comments. Exceptforoverallsizedifferences,littlemorphologicalvariability is evident. Of the worker hypotypes above, two are of similar size but the third [SG] is considerably larger; in the material at hand some workers are much smaller than given here, and some almost attain the size of small queens which is not unusual. As far as coloration is concerned, the thoracic dorsum of the queen varies from a rich ferruginous brown to reddish or (even) tawny yellow, while the abdomen is much less variable except for the amount or extent of yellowish pile mid-basally on T2; this condition is usually less noticeable on the workers. The male is the most variable chromatically, especially on the abdomen; sometimes the thoracic dorsum (which is usually drab yellow) tends to be brownish yellow or pale yellowish brown. Except for male abdominal T4-7, the remaining terga might be predominantly tawny or drab yellowish, especially on T1 and T2.