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 24-25 mm in length, workers 15-21 mm. Head long, cheek longer than wide; mid-leg basitarsus with back far corner acutely pointed but not narrow, hind-leg tibia with outer surface flat and hairless (except for fringe) forming a pollen basket; hair on face and top of head black or sometimes with some yellow hair intermixed; upper surface of thorax with yellow strongly intermixed in the black spot or band between the wings, sides of thorax predominantly black; T1 with yellow hairs more dominant on sides, T2 yellow, T3 usually yellow, T4-5 usually black. Males 16-19 mm in length; eyes greatly enlarged and strongly convergent on the upper part, much larger than eyes of any female bumble bee; antennae short, flagellum 2X longer than scape; hair color pattern similar to queens and workers, but T6-7 extensively orange (Koch et al. 2012, Williams et al. 2014).

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

Please see the Montana State Entomology Collection's Key to Female Bumble Bees in Montana. Females told from other Montana Bombus by combination of the outer surface of hind-leg tibia concave and lacking hair (except for fringe), forming a pollen basket; cheek longer than wide; face predominantly with black hairs; T2 yellow, T3 yellow at least in the middle, T4-5 with black hairs; hairs between wing bases predominantly yellow, if black hairs present then forming a small central spot.

Inhabits open grassy prairie, sagebrush steppe, and montane meadows, usually at lower elevations but reaching above treeline to alpine tundra (Macior 1974, Bauer 1883, Mayer et al. 2000, Kearns and Oliveras 2009, Cook et al. 2011, Miller-Struttmann and Galen 2014, Williams et al. 2014). Also commercial highbush blueberry (Vaccinium corymbosum) crops to a lesser extent (Ratti et al. 2008).

Feeds on a wide variety of flowers, including Agastache, Astragalus, Balsamorhiza, Ceanothus, Cirsium, Crataegus, Dipsacus, Dodecatheon, Frasera, Helianthus, Iris, Lonicera, Lupinus, Malus, Medicago, Melilotus, Mentha, Monarda, Oxytropis, Penstemon, Phacelia, Primula, Ranunculus, Ribes, Salvia, Solidago, Spiraea, Stachys, Taraxacum, Thermopsis, Trifolium, Triteleia, Vaccinium and Vicia (Macior 1968, Beattie et al. 1973, Macior 1974, Bauer 1983, Thorp et al. 1983, Mayer et al. 2000, Ratti et al. 2008, Koch et al. 2012, Miller-Struttmann and Galen 2014, Williams et al. 2014). A minor contributor to pollination of commercial highbush blueberry (Vaccinium corymbosum) in southern British Columbia (Ratti et al. 2008).

Nests underground, but also infrequently on the surface (Williams et al. 2014). Favors underground sites in southern Alberta when given a choice of artificial hives in which to establish nests; 85.7% of 21 nests built underground (Hobbs 1965a). Nests (n = 31) generally established in late May to early June (range: 17 May to 20 June). For first broods, single eggs are laid per cell; the number of larvae in first broods averages 12.4 (n = 16 colonies). Number of days required by queens to produce workers averages 24-39 (n = 14 records across four years). For second and later broods, queens lay a single egg per cell. Colonies are small; in three colonies producing queens, 55, 86, and 139 cocoons were present, and 43 and 58 cocoons were present in two other colonies failing to produce queens. Queens hibernate overwinter at depths of 8-18 cm in well-compacted soil, sometimes as many as four queens in one hibernaculum (Hobbs 1965a). Males and queens are in close contact in nests, but do not mate there. Males patrol territories and perch on tops of shrubs or other vegetation projecting above the surroundings, returning repeatedly for several days to the same perches in territories, and pursue passing insects in search of queens. Queens are mounted in midair and taken to the ground; neighboring territorial males when encountered are butted and sometimes grappled with (Hobbs 1965a, Alcock and Alcock 1983, O'Neill et al. 1991). Nest are sometime parasitized by the cuckoo bumble bees, Bombus insularis and B. suckleyi; parasitic queens sometimes kill host queens (Hobbs 1965a, Williams et al. 2014). Ants also destroy some nests.