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, small-sized bumble bee: queens 15-20 mm in length, workers 9-14 mm. Hair long, shaggy, uneven; head length medium, cheek as long as wide; mid-leg basitarsus with back far corner rounded, hind-leg tibia outer surface flat and hairless (except fringe) forming pollen basket; hair on upper surface of thorax yellow but densely intermixed with black especially between wings and on scutellum; T1 yellow, T2 with yellow often narrowly interrupted by black especially at back or intermixed with black, T5 almost entirely pale brownish yellow (yellow and orange hairs intermixed). Males 9-14 mm in length; eyes similar in size and shape to eyes of any female Bombus; antennae medium length, flagellum 3X longer than scape; hair color pattern similar to queens and workers, but upper side of thorax with more yellow hair intermixed with black between wings; T3 usually with pale fringe of yellow hair at back or entirely yellow (Koch et al. 2012, Williams et al. 2014).

Across the range, queens reported March to September, workers April to September, males April to October (Williams et al. 2014). In Washington, queens reported March to August, workers May to October, males April to October (Koch et al. 2012); in California, queens late January to early December, workers early March to late September, males early April 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 Montana Bombus by a combination of hind-leg tibia outer surface concave and hairless (except fringe) forming a pollen basket; T1-2 and T4-5 with yellow and/or orange hairs; cheek as long or slightly longer than wide; scutum cloudy (yellow and black hairs intermixed); scutellum distinctly darker than scutum (many black hairs intermixed throughout).

Open grassy prairie, montane meadows, urban gardens and parks, commercial blueberry and cranberry cropland (McFrederick and LeBuhn 2006, Ratti et al. 2008, Wojcik et al. 2008, Williams et al. 2014).

Feeds on a variety of flowers, including Aquilegia, Brassica, Ceanothus, Cirsium, Epilobium, Lathyrus, Lupinus, Phacelia, Rhododendron, Ribes, Rosa, Rubus, Salix, Solidago, Stachys, Symphyotrichum, Vaccinium and Vicia (Thorp et al. 1983, Ratti et al. 2008, Wilson et al. 2010, Koch et al. 2012, Williams et al. 2014). A minor pollinator in crops of commercial Vaccinium (highbush blueberry and cranberry) in southern British Columbia (Ratti et al. 2008).

Little information. Nests built underground, presumably in rodent burrows (McFrederick and LeBuhn 2006). Males patrol circuits in search of queens (Williams et al. 2014).