Montana Field Guide

For definitions and diagrams of bumble bee morphology please see the Montana State Entomology Collection's Bumble Bee Morphology page. A long-tongued, large-sized bumble bee: queens 20-24 mm in length, workers 11-18 mm. Head long, cheek distinctly longer than wide; mid leg basitarsus with far back corner narrowly extended in a spine, outer surface of hind leg tibia flat and lacking hair (except fringe) forming pollen basket; hair of face pale whitish and lighter than hair on T1; sides of thorax predominantly black, upper surface pale at least anterior to wings and bordering a black band between wings; T1-5 straw yellow or brownish orange. Males 10-16 mm in length; eyes similar in size and shape to eyes of any female bumble bee; hair color pattern similar to queens and workers, but sides of thorax with only a few black hairs intermixed toward back; T6 pale at sides (Koch et al. 2012, Williams et al. 2014).

Across range, queens reported April to October, workers May to September, males May to October (Williams et al. 2014). In Utah, queens reported May to August, workers May to September, males June to September (Koch et al. 2012); in California, queens early May to early September, workers late May to late August, males late June to early September (Thorp et al. 1983).

Please see the Montana State Entomology Collection's Key to Female Bumble Bees in Montana. Females told from other Montans Bombus by a combination of outer surface of hind leg tibia concave and hairless (except fringe) forming pollen basket; cheek longer than wide; yellow or pale white hairs on face, sometimes with black giving a cloudy appearance; T1-5 straw-yellow or orange-brown.

Grassland, fields, sagebrush steppe, aspen parkland, riparian woodland, montane meadows, granitic soil types, above treeline in alpine tundra (Hobbs 1966b, Macior 1974, Richards 1978, Bauer 1983, Wilson et al. 2010, Cook et al. 2011, Miller-Struttmann and Galen 2014, Williams et al. 2014). Also infrequently in commercial Vaccinium croplands (Ratti et al. 2008).

Feeds on a variety of flowers, including Aconitum, Agastache, Astragalus, Balsamorhiza, Castilleja, Cirsium, Cleome, Delphinium, Dipsacus, Erysimum, Frasera, Gentiana, Geranium, Helianthus, Iris, Lathyrus, Linaria, Lonicera, Medicago, Melilotus, Mentha, Myosotis, Orthocarpus, Oxytropis, Pedicularis, Penstemon, Phacelia, Rhus, Rudbeckia, Solidago, Thermopsis, Trifolium, Triteleia, Vaccinium and Vicia (Hobbs 1966, Beattie et al. 1973, Macior 1974, Bauer 1983, Thorp et al. 1983, Mayer et al. 2000, Ratti et al. 2008, Wilson et al. 2010, Pyke et al. 2012, Koch et al. 2012, Miller-Struttmann and Galen 2014, Williams et al. 2014, Ogilvie and Thomson 2015). An infrequent visitor to commercial Vaccinium (highbush blueberry) crops in southern British Columbia (Ratti et al. 2008).

Nests built underground, on ground surface, or above ground. In aspen parkland of southern Alberta, 29.3% of 99 nests built underground, 39.4% on the ground surface, and 31.3% above ground (Richards 1978). In wooded foothills of the Alberta Rocky Mountains, Hobbs (1966b) reported this species in 29 underground and 74 surface hives, and later in 30 underground and 37 surface hives when given a choice at each hive location. Queens sometimes invade nests of conspecifics and attempt to usurp them. Nests are established in southern Alberta from late May to mid July (Hobbs 1966b, Richards 1978); a minority of nest entrances are camouflaged. This bumble bee species does not produce large colonies. First broods average 13 pupae, which require an average of 23-26 days for rearing the first workers. In second and third broods, an average of 3.6 eggs are laid per cell, later broods may contain up to 8 eggs per cell. Typically, only two broods of workers are produced; average number of pupae (cocoons) per colony per year ranged from 68 to 168. Males hover and perch outside nest entrances and wait to mate with emerging queens, possibly mating within nests (Hobbs 1966b). Parasitized by the cuckoo bumble bees Bombus insularis, B. suckleyi, and B. fernaldae, which sometimes succeed in having the host workers raise their young (Hobbs 1966b, Williams et al. 2014).