Montana Field Guide

For definitions and diagrams of bumble bee morphology please see the Montana State Entomology Collection's Bumble Bee Morphology page. A medium-tongued, medium-sized bumble bee: queens 19-20 mm in length, workers 11-14 mm. Hair short and even; head length medium with cheek as long as wide; mid-leg basitarsus back far corner rounded, hind-leg tibia outer surface flat and hairless (except black fringe hairs) forming pollen basket; hair of face and top of head predominantly yellow; upper side of thorax yellow anterior and posterior to black band between wing bases; T1 yellow, T2-3 red to orange, T4 yellow, T5-6 black. Males 9-13 mm in length; eyes similar in size and shape to eyes of any female bumble bee; antennae of medium length, flagellum 2.5-3X longer than scape; hair color pattern similar to queens and workers, but the upper side of thorax often with many yellow hairs intermixed with black in the band between the wings (Koch et al. 2012, Williams et al. 2014).

Across the range, queens and workers reported March to October, males April to November (Williams et al. 2014). In California, queens reported late March to late September, workers late May to early October, males late May to late October (Thorp et al. 1983); in Utah, queens March to early August, workers March to late September, males May to late October (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 a combination of outer surface of hind-leg tibia concave and hairless (except fringe), forming pollen basket; T2-3 red or orange, possibly with yellow hairs intermixed in the middle; scutum in front of wing bases predominantly yellow or pale yellow hair; cheek as long as wide; face with yellow hairs at least centrally; scutellum with yellow hairs only.

High desert shrub, grassland and mixed prairie, irrigated prairie and riparian woodland, prairie parkland, sagebrush shrubsteppe, subalpine forest meadows, rarely above treeline in alpine tundra (Hobbs 1967, Macior 1974, Bowers 1985, Cook et al. 2011, Miller-Struttmann and Galen 2014, Williams et al. 2014).

Feeds on a variety of flowers, including Allium, Artemisia, Asclepias, Astragalus, Caragana, Chrysothamnus, Cirsium, Cleome, Daucus, Dodecatheon, Ericameria, Erigeron, Eriogonum, Gutierrezia, Helianthus, Hydrophyllum, Iris, Linaria, Lupinus, Medicago, Melilotus, Mentha, Mentzelia, Mertensia, Penstemon, Phacelia, Prunus, Ribes, Rosa, Rudbeckia, Salix, Sedum, Senecio, Solidago, Symphyotrichum, Taraxacum, Thermopsis, Trifolium and Vicia (Macior 1974, Thorp et al. 1983, Koch et al. 2012, Williams et al. 2014, Miller-Struttmann and Galen 2014).

Nests mostly underground. 90.3% of 31 hives built underground in southern Alberta, the remainder on the ground surface; most nests established mid- to late May. Mean numbers of eggs, larvae, and pupae in first broods were 9.3, 8.2, and 9.4 respectively; mean number of eggs laid per cell of second and third broods was 3.6. Largest hives contained up to 531 cocoons (Hobbs 1967). A nest in New Mexico in early August contained 515 workers, one queen, 709 empty worker cocoons, 101 larvae, 119 queen pupae, 117 worker pupae, and 308 eggs in the brood mass; the nest was build on the ground in an old woodrat nest of shredded wood fiber under a storage shed floorboard (Medler 1959).