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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, 23.0 mm; width at wing bases, 10.5 mm; abdomen, 12.0 mm, width across T2, 10.0 mm; front wing length, 17.5 mm, width, 6.0 mm. Head: Frontal outline (excluding mouthparts) trapezoidal, little higher than wide, arcuately rounded dorsolaterally; vertical region slightly concave laterad of ocelli; ocelli positioned in nearly straight transverse line considerably below supraorbital line, the interocellar line nearly equal to the ocellocular line; ocular half of ocellocular area weakly irregularly punctate, ocellar half smooth and polished, vertex behind and laterad of ocelli irregularly punctate; outline of compound eye ventrally arcuately rounded, acutely rounded dorsally, nearly 3 times higher than greatest breadth; clypeus almost i wider than high, somewhat concave laterally and dorsally, weakly convex over median anterior area, rather evenly sculptured with irregular medium punctures; labrum about 2i times wider than thick, its anterior (ventral) margin broadly arcuate, the labral tubercles roughly sculptured, their weak summits directed slightly ventromesad, the intertubercular depression not sharply defined and less than length of FI; malar space little more than li times longer than distance between (and including) mandibular articulations, smooth and polished, area beneath compound eye weakly irregularly sculptured, the ventral half ad�joining mandibles convex; flagellum nearly twice as long as scape, FI distinctly longer than F2 and little longer than F3, about f as long as F2-3 combined. Legs: Mesobasitarsite elongate rectangular, nearly 3 times longer than greatest width of segment, its outer surface moderately concave longitudinally, the distoposterior angle subacute and not extended beyond distoanterior angle; outer hind tibial surface weakly unevenly concave, microscopically alutaceous, weakly concave and much more alutaceous distoposteriorly; metabasitarsite somewhat less than 2f times as long as widest dimension, the outer surface shallowly concave longitudinally, the posterior margin evenly weakly arcuate to distal third then nearly straight, the distoposterior angle roundly acute and somewhat extended beyond rounded distoanterior angle. Pubescence: Rather long and loose throughout, longer and more uneven posteriorly on mesoscutellum and over distal abdominal terga; corbicular fringe long, moderately dense, nearly straight except distally, the longest hairs 1� times as long as greatest width of corbicula; metabasitarsal posterior fringe rather long and arcuate on basal half, beyond short to absent distally. Color: Head black with intermixture of lighter pile on postvertex; thorax anteriad of tegulae yellow (or ochraceous yellow) intermixed with black (normally this area is entirely ochraceous yellow), the interalar area widely covered with black, without sharply delimited usually rather broad interalar black band that is typical of this species, the posterior half of mesoscutellum mostly tawny yellow. Abdominal Tl-2 light ochraceous yellow, remaining terga black with intermixture of some paletipped hairs laterally on T3-6.
Worker. Length, 15.0 mm; width at wing bases, 6.0 mm; abdomen, 8.0 mm, width across T2, 6.5 mm; front wing length, 11.0 mm, width, 4.0 mm. In all other morphological respects relatively similar to the queen. Color: Thorax dorsally and laterally ochraceous yellow with rather narrow interalar black band. Abdominal Tl-2 ochraceous yellow, T3 especially, and terga beyond with burnt sienneous yellow intermixed with black. The few workers seen indicate that this caste is without pale pubescence on abdominal T3-6, but has a sharply defined interalar black band, as in the typical queen.
Male. Length, 18.0 mm; abdomen, 10.0 mm, width across T2, 7.0 mm; width at wing bases, 7.0 mm; front wing length, 15.5 mm, width, 5.0 mm. Head: Frontal outline triangular (excluding mouthparts), nearly as wide as high; compound eye rather small, about 21 times higher than widest dimension, rounded below and narrowly unevenly rounded above, inner margin nearly straight, the outer margin weakly concave outwardly; vertex weakly concave, roughly irregularly punctate; ocular half of ocellocular area with coarse well-separated punc� tures, the ocellar half smooth and polished; ocelli in nearly straight line, situated slightly below supraorbital line, somewhat closer to one another than widest dimension of each; malar space about If times longer than distance between (and including) mandibular articulations, irregularly convex (more evenly and strongly so over ventral half) and polished with micro�pubescence especially on posterior half; labrum little more than twice as wide as thick, its ventral margin broadly rounded laterally, slightly concave medially, the surface irregularly sculptured, with weak �crescent� shaped polished tubercles, beneath transversely indented across, entirely covered with sparse irregular short pubescence; flagellum almost 3 times longer than scape, FI distinctly longer than F2, only f as long as F3. Legs: Mesobasitarsite 3f times longer than greatest width, most of its outer surface evenly concave longitudinally, the obtusely rounded distoposterior angle in recess of distoanterior angle, posterior fringe average length on basal half longer than width of segment, sharply shorter and even along distal half; metabasitarsite slightly less than 3f times as long as widest dimension of segment, shallowly concave longitudinally over most of posterior two-thirds, the distoposterior angle obtusely rounded, posterior margin very weakly evenly arcuate throughout, its slightly arcuate fringe averaging distinctly longer than greatest width of segment. Pubescence: Generally shaggy, long, loose, un� even throughout. Genitalia, seventh and eighth abdominal sterna (PI. XII). Color: Vertical region of head, thorax anteriad of tegulae, upper area of mesopleura, most of scutellum and abdominal Tl-2 sienneous yellow, remainder of body dull black, the posterior fringes of hind tibia and metabasitarsite, likewise some scattered hairs on the distal abdominal terga, tinged with burnt sienna.
Comments. No significant morphological variations have been noted in either female (caste) or male. In length, queens are 21.0-23.0 mm, and males 16.0-19.0 mm. Slight variation in length of the queen malar space is evident; and, in the male, minor structural differences exist especially with respect to the inner outline of the squama; however, none of these poses a problem in the identification of this species. Insufficient worker material precludes remarks on morphological variation but, pre� sumably, the length of the malar space in this caste varies slightly as in the queen. In the queen the following chromatic variations occur: The yellow might be drab, viri- descent, or golden on the thorax and basal abdominal terga, and the pubescence on the lower portions of the mesopleuron is sometimes tinged with burnt sienna; the interalar area is normally rather wide, well-defined black, but varies to a broad black area with suffused margins well extended onto the mesoscutum anteriad of tegulae and posteriad onto much of the scutellum; some specimens show a noticeable amount of dull yellow on the postvertex, others have varying amounts of noticeable drab yellow or pale burnt sienna on the distal half of abdominal T3 and numerous hairs so pale-tipped on T4-6, though ordinarily T3-6 in the queen of this species are wholly black. Similar chromatic variations should be expected in the worker. Chromatically, the male is much more diverse than the female; the vertical region of the head, most of the mesopleuron, and abdominal Tl-3 sometimes are covered with pale or drab yellow, and T4-7 might be variously covered with pale to pale-tipped black hairs. The interalar black band of the male is sometimes narrowly weakened and very in� definite (more so than in the female); however, on most males this band is rather wide and without sharp anterior and posterior margins.
Workers of this species are rare in Western Hemisphere collections. This pri�marily is due to the inherent characteristic tendency of overwintered queens to usurpe the nest of a realted species (M. (M.) polaris (Curt.)) and under seasonable circumstances the production of its sexuals (queens and males) seems to be all that is possible at most investigated locations in the high Canadian arctic (cf. Milliron and Oliver 1966).
Melanie queens of this species have the thorax predominantly black, dorsally with the lighter pubescence reduced to an intermixture of black and dull yellow on the pronotum, anterior margin of mesonotum and along the posterior margin of the scutellum; melanic males have dull burnt sienna intermixed with black on the thoracic dorsum anteriorly, on the scutellum, and on abdominal Tl-2 in place of the usual yellow; such specimens are without any defined interalar black band which is also the condition in melanic queens.
It should be emphasized that the �yellow�-colored areas of most Eastern Hemi� sphere specimens is deeper (golden to orange-yellow) in contrast to the dull or viridescent yellow common to Western Hemisphere specimens of this species.
Extracted from: Cockerell T.D.A., (1894). Two New Bees. The Canadian Entomologist pp. 35-37.
FEMALE . —Length about 19 mm.; width of abdomen 8 ; ocelli small, as in Bombus, s. sir.; clypeus shining, convex, with sparse punctures of unequal
sizes, some very faint ; malar space about one-fourth broader than long ; upper outer face of mandibles with three strong ridges ; labrum with a
pair of widely-separated transversely oval bosses ; flagellum short, third antennal joint about as long as 4 5 ; mesothorax densely punctured, except in middle, where it is smooth and shining ; hair of head black, of thorax in front, pleura and scutellum, tawny-yellow, but a very broad black band between the wings ; wings strongly reddened, a dark cloud at apex
of marginal cell ; abdomen rather narrow, with coarse black hair, except on first segment and anterior middle (tapering laterally) of second, where
it is tawny-yellow ; hair of legs black, spinules on tarsi ferruginous.
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