Montana Field Guide

For definitions and diagrams of bumble bee morphology please see the Montana State Entomology Collection's Bumble Bee Morphology page. A short-tongued large-sized bumble bee: queens 22-26 mm in length, workers 12-22 mm. Hair very short and even in length; head short with cheek shorter than wide; mid-leg basistarsus with back far corner rounded, outer surface of hind-leg tibia flat and lacking hair (except at fringe) forming a pollen basket; hair on sides of thorax black, upper side of thorax lacking black band between wings; T1-2 yellow, T3 with at least yellow in the middle, T4-5 black. Males 15-20 mm in length; eyes greatly enlarged, much longer than eyes of any female bumble bee, and weakly convergent in the upper part; antennae long, flagellum nearly 3X longer than scape; hair color pattern similar to queens and workers, with T3 entirely yellow (Koch et al. 2012, Williams et al. 2014).

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

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

Occupies prairie grasslands, arid shrublands, lower montane meadows, rarely reaches above treeline to alpine tundra (Macior 1974, Kearns and Oliveras 2009, Wilson et al. 2010, Miller-Struttmann and Galen 2014, Williams et al. 2014).

Feeds on a variety of flowers, including Asclepias, Astragalus, Balsamorhiza, Brassica, Chrysothamnus, Cirsium, Cleome, Dalia, Delphinium, Ericameria, Erysimum, Frasera, Geranium, Helianthus, Iris, Lupinus, Melilotus, Mentzilia, Monarda, Oxytropis, Penstemon, Salvia, Senecio, Taraxacum, Thermopsis, and Trifolium (Macior 1974, Thorp et al. 1983, Wilson et al. 2010, Koch et al. 2012, Miller-Struttmann and Galen 2014, Williams et al. 2014). Also an important native pollinator of alfalfa crops (Medicago sativa) throughout the inter-mountain west (Bohart and Knowlton 1952).

Nests built underground; males perch and pursue moving objects in search of queens (Williams et al. 2014). Otherwise, little information. Parasitism by cuckoo bumble bees not described.