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, 26.0 mm; width at wing bases, 11.0 mm; abdomen, 14.0 mm, width across T2, 12.0 mm; front wing length, 21.5 mm, width, 8.0 mm. Head: Frontal outline (excluding mouthparts) narrowly elongate trapezoidal, the upper angles rounded, little more than H times higher than greatest width, the vertical region rather strongly inclined toward occiput with surface mostly flat to weakly concave and rather well covered with small punctures; ocellocular area mostly smooth with only the approximate ocular half very weakly and sparsely punctate; ocelli about equal in size, situated near to one another in a weak arc just below supra orbital line; compound eyes somewhat more broadly and evenly rounded below than above, their inner margins subparallel to slightly divergent below; malar space at least 11 times longer than distance between (and including) mandibular articulations, its surface rather weakly and uneven ly convex and practically free of noticeable punctation; labrum nearly twice as wide as greatest thickness, its ventral margin broadly arcuate, the labral shelf sharp and extending well onto each of the rather prominent tubercles which are irregularly punctate, flattened below and mesally conical, their summits separated by a somewhat shallow intertubercular depression wider than length of FI;flagellum little less than twice as long as scape, FI distinctly longer than subquadrate F2 which is more than half the length of F3, F2, and F3 combined only little longer than FI; clypeus rather evenly convex, well but not densely covered with medium punctures, its median height about equal to widest ventral dimension. Legs: Mesobasitarsite nearly rectangular, about 5 times longer than widest part, its outer surface concave near mid-longitudinal axis, the distal end only shallowly emarginate with blunt distoanterior angle only slightly in recess of acute disto- posterior angle; outer surface of hind tibia somewhat alutaceous, convex longitudinally near anterior margin, behind flat to weakly concave, the widest part about equal to longest hairs of corbicular (posterior) fringe; metabasitarsite with most of outer surface rather deeply concave longitudinally, the posterior margin weakly arcuate along basal half and straight beyond, the acute distoposterior angle extended noticeably beyond more blunt distoanterior angle, with shallow angulate emargination between. Pubescence: Rather short, dense and even except slightly longer and looser on head, posterior area of scutellum, on abdominal T3-5 and abdominal venter; corbicular fringe rather dense, mostly composed of weakly arcuate hairs; metabasitarsal posterior fringe not long, the longest hairs occurring on basal half of margin, beyond becoming very short and sparse distally. Color: Entirely black (cf. under Comments). Wings black with violaceous reflections under certain light.
Worker. Length, 19.0 mm; width at wing bases, 9.0 mm; abdomen, 9.0 mm, width across T2, 9.0 mm; front wing length, 16.5 mm, width, 6.0 mm. Otherwise, comparable to the queen in all important respects (cf. under Comments).
Male. Length, 18.5 mm; width at wing bases, 7.0 min; abdomen, 10.0 mm, width across T2, 8.0 mm; front wing length, 16.5 mm, width, 5.5 mm. Head: Frontal outline (excluding mouth- parts) narrowly trapezoidal, about as high as widest dimension, the vertical region nearly flat, moderately inclined toward occiput, well covered with irregular medium punctures; ocelli posi tioned in a weak arc, separated from each other by little less than their diameters, the lateral ones touching supraorbital line; ocellar half of ocellocular area smooth, the ocular half with few medium punctures; compound eyes somewhat more broadly rounded below than above, their inner margins subparallel; malar space for the most part weakly convex and practically smooth, at least li times as long as distance between (and including) mandibular articulations; labrum more or less rectangular, about 2£ times wider than greatest thickness, its ventral margin mostly straight, its surface weakly sculptured and with transverse shallow concavity below inconspicuous callosi ties; flagellum near 5 times longer than scape, most segments weakly crenulate, FI little more than i of F2 which is subequal to F3, FI and 2 combined little longer than F3. Legs: Meso- basitarsite more or less rectangular, nearly 4 times longer than widest part, distal end subtruncate, the distoposterior angle somewhat sharper than distoanterior one and noticeably in recess of it; metabasitarsite similar but somewhat wider, its posterior margin weakly arcuate, the distal end weakly emarginate between distal angles which are equally extended, the distoposterior one the sharper (subacute), the outer surface alutaceous and with short well separated hairs. Pubes cence: Character similar to that of the queen and worker except stronger pile on the clypeus is somewhat denser, that on abdominal terga is little shorter and more even and not quite as dense; mesobasitarsal posterior fringe mostly of medium length, the longest hairs more than \ as long as widest part of segment; metabasitarsal posterior fringe very short throughout. Genitalia, seventh and eighth abdominal sterna figured (PI. XIV). Color: Black except fine pile on face, as well as some on lower thoracic pleura, venter and some on coxae, trochanters, and femora pallid (entirely or in part tinged with white or pale grey). Wings colored much as those of the queen.
Comments. Except for the rather wide range in size, especially of the workers, no morphological variation worthy of note has been detected in this taxon. Some of the smaller workers seen measure considerably less than one-half of that given here, whereas the larger workers are difficult to segregate from small queens. Infrequent chromatic variations, on the other hand, might be striking; specimens displaying these usually have part of an abdominal tergum (or terga) dull brownish coppery red, and sometimes the entire body is so colored without any evidence of the normal black. The presence of yellowish pile on any part of the body is very rare, and then in the form of only traces. I have regarded all these off-colour specimens as aberra tions or freaks (c/. Milliron 1971) .*