Montana Field Guide

For definitions and diagrams of bumble bee morphology please see the Montana State Entomology Collection's Bumble Bee Morphology page. Small body size, queens 16-19 mm, workers 10-16 mm; face square, of medium head length with cheek as long as wide, tongue length medium; basitarsus of mid-leg with back far corner rounded, outer surface of hind-leg tibia flat and without hair but with a fringe of hair forming a pollen basket; hair length medium and uneven, hair yellow on face and top of head, thorax with many black hairs densely mixed in front pale band, the black band between the wings not sharply defined, the back area of thorax variably yellow; T1 yellow, T2-3 orange (sometimes with black hairs intermixed), T4-5 black (often with yellow intermixed); if T2-3 extensively black then T4-5 extensively yellow and T5 yellow on sides. Males 11-14 mm, eyes similar in size and shape to any female bumble bee; antenna medium in length, flagellum 3x longer than the scape; color pattern similar to queen and worker (Koch et al. 2012, Williams et al. 2014)

Queens active February to August, workers and males March to September (Koch et al. 2012, Williams et al. 2014). In California, queens active early February to early October, workers late April to late September, males late June to early October (Thorp et al. 1983).

Please see the Montana State Entomology Collection's Key to Female Bumble Bees in Montana. Distinguished from other Bombus by combination of outer surface of hind-leg tibia concave and forming a pollen basket, anterior edge of thorax (scutum) to the distinct black band between the wings with mix of yellow and black hairs giving a cloudy appearance, T2-3 with red or orange hairs (T2 not intermixed with yellow) and corbicular (pollen basket) fringe hairs black (or possibly orange at the tips).

Predominantly open grassy areas and mountain meadows, but also sagebrush steppe to alpine fell-field and tundra (Macior 1974, Bauer 1983, Shaw and Taylor 1986, Cook et al. 2011, Williams et al. 2014). In southern Alberta, B. melanopygus is found in foothill and mountain forest zones (Hobbs 1967). In southern Idaho, trapped significantly more often in areas with sagebrush canopy < 10% than where canopy > 25% (Cook et al. 2011). Also frequents commercial highbush blueberry and cranberry crops in southern British Columbia (Ratti et al. 2008). Two nests in southern Alberta were constructed in woods-meadow ecotone (Richards 1978).

Feeds on a wide variety of flowers, including Achillea, Allium, Anaphalis, Arctostaphylos, Arenaria, Aster, Berberis, Calypso, Castilleja, Ceanothus, Chionophila, Crataegus, Dodecatheon, Epilobium, Ericameria, Erigeron, Eriogonum, Haplopappus, Iris, Linaria, Lonicera, Lupinus, Malus, Mertensia, Microseris, Myosotis, Origanum, Oxytropis, Pedicularis, Penstemon, Phacelia, Phlox, Polygonum, Rhododendron, Ribes, Rubus, Salix, Salvia, Sedum, Senecio, Solidago, Symphoricarpos, Taraxacum, Trifolium, Vaccinium, Vicia and Wyethia (Macior 1974, Ackerman 1981, Bauer 1983, Thorp et al. 1983, Shaw and Taylor 1986, Ratti et al. 2008, Wilson et al. 2010, Koch et al. 2012, Miller-Struttmann and Galen 2014, Williams et al. 2014).

One of the earliest bumble bee species to begin nesting and produce males. Nests built underground, and sometimes above ground in bird houses and building insulation (Williams et al. 2014). Underground nests favored in southern Alberta (Hobbs 1967); two nests were begun 7 June. Two other nests in southern Alberta were started on 8 and 10 May (Richards 1978). Nest parasitism by cuckoo bumble bees has not been described.