Montana Field Guide

For definitions and diagrams of bumble bee morphology please see the Montana State Entomology Collection's Bumble Bee Morphology page. A small-sized species with a medium-long tongue: queens 16-18 mm, workers 10-13 mm. Head length medium, with cheek slightly longer than broad; mid leg basitarsus with back far corner rounded; outer surface of hind leg tibia flat and without long hair but with long fringes at edges, forming a pollen basket; yellow hair on the upper side of head and anterior part of thorax; T1-2 entirely yellow or with black at front and middle; T3-4 orange; T5-6 mostly black. Male 12-14 mm; eye similar in size and shape to any female bumble bee; antennae medium length with flagellum 2.5-3X longer than scape. hair color pattern similar to queens and workers, although lacks black hairs at back of yellow band on thorax; T3-4 red without any black hairs; T5-7 mostly red to mostly black (Williams et al. 2014).

Queens reported across the range from March to October, workers and males from April to September (Williams et al. 2014). In Utah, queens reported March to June, workers March to September, males May to September (Koch et al. 2012). In California, queens reported late April to early September, workers early May to early September, males early June to early October (Thorp et al. 1983). Peak abundance of workers in Palouse Prairie remnants of western Idaho and eastern Washington was during late July (Hatten et al. 2013).

Please see the Montana State Entomology Collection's Key to Female Bumble Bees in Montana. Females distinguished from other Montana Bombus by a combination of concave and shiny outer surface of hind leg tibia with pollen basket present; cheek slightly longer than wide; face with yellow hair; mostly yellow hair on thorax anterior to wind bases; T1-2 yellow and T3-4 orange.

Open grassy prairies and sagebrush steppe to montane and alpine meadows (Macior 1974, Bowers 1985, Norment 1988, Kearns and Oliveras 2009, Cook et al. 2011, Hatten et al. 2013, Williams et al. 2014). Greatest abundance in southern Alberta in irrigated prairie and wooded riparian (Hobbs 1967). A nest in southern Alberta initiated in woods-meadow ecotone (Richards 1978). Relatively rare in commercial highbush blueberry crops in southern British Columbia (Ratti et al. 2008).

Feeds on a variety of flowers, including Aconitum, Agastache, Allium, Anaphalis, Astragalus, Balsamorhiza, Calypso, Caragana, Centaurea, Chrysothamnus, Cirsium, Cleome, Collinsia, Delphinium, Dipsacus, Dodecatheon, Epilobium, Ericameria, Erigeron, Eriogonum, Erysimum, Frasera, Geranium, Haplopappus, Helianthus, Iris, Linaria, Lupinus, Malus, Melilotus, Mentha, Mentzelia, Mertensia, Mimulus, Monarda, Onosmodium, Orthocarpus, Oxytropis, Penstemon, Phacelia, Ribes, Robinia, Rosa, Rubus, Rudbeckia, Sisyrinchium, Symphoricarpos, Symphyotrichum, Taraxacum, Thermopsis, Trifolium, Triteleia, Vaccinium and Vicia (Macior 1974, Ackerman 1981, Thorp et al. 1983, Norment 1988, Mayer et al. 2000, Ratti et al. 2008, Wilson et al. 2010, Koch et al. 2012, Miller-Struttmann and Galen 2014, Williams et al. 2014). Infrequent visitor to commercial Vaccinium in southern British Columbia (Ratti et al. 2008).

Nests underground (Hobbs 1967, Williams et al. 2014). Nests initiated mostly in late May to early June in southern Alberta (Hobbs 1967, Richards 1978); the mean number of larvae and pupae of firsts broods was nine. Males, upon emerging, patrol circuits in search of queens. Parasitism of nests by cuckoo bumble bees has not been reported but is likely (see comments in Hobbs 1967).