Montana Field Guide

For definitions and diagrams of bumble bee morphology please see the Montana State Entomology Collection's Bumble Bee Morphology page. [Formerly classified as B. bifarius, now considered B. vancouverensis nearctica in Montana.] A medium-tongued, small-sized bumble bee: queens 15-19 mm in length, workers 8-14 mm. Head medium length, cheek just shorter than wide; mid leg basitarsus back far corner rounded, outer surface of hind leg tibia concave and hairless (except fringe) forming pollen basket; hair on face yellow or white, sometimes with many black hairs intermixed on upper side of head; yellow or white hairs of thorax anterior to wings sometimes intermixed with black, giving a cloudy appearance; wide black wedge of black hairs projects posteriorly on thorax to back edge; sides of thorax with black hairs in at least the lower third; hind leg fringes of pollen basket pale orangy-brown, or if T3 black then fringe may be black; T1 yellow or white, T2 usually with a patch of black hair in front middle (although T2-3 may show partial or complete replacement of red hairs with black), T4 yellow, T5 black with yellow only on extreme side and back fringes. Males 8-13 mm in length; eyes similar in size and shape to eyes of any female bumble bee; antennae medium length, flagellum 3X longer than scape; hair color pattern similar to queens and workers, occasionally T1-2 and T4-5 mostly yellow, T3 and T6 mostly black (Koch et al. 2012, Williams et al. 2014).

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

Please see the Montana State Entomology Collection's Key to Female Bumble Bees in Montana. [Former B. bifarius now considered this species in Montana.] Females told from other Montana Bombus by a combination of outer surface of hind leg tibia concave and hairless (except fringe) forming a pollen basket; pollen basket fringe orange or brown; exoskeleton of hind leg basitarsus brownish orange and often lighter than tibia; scutum anterior to wings with yellow and black hairs intermixed, giving a cloudy appearance; T2-3 with red or orange hairs, T2 with black hairs at least in middle.

Prairie, grassland, riparian woodland, sagebrush steppe, chaparral, urban parks and gardens, mountain meadows to above treeline in alpine tundra (Hobbs 1967, Macior 1974, Bauer 1983, McFrederick and LeBuhn 2006, Cook et al. 2011, Williams et al. 2014). Abundance in sagebrush steppe tends to be inversely related to percent canopy cover of sagebrush (Cook et al. 2011).

Feeds on a variety of flowers, including Achillea, Agoseris, Allium, Anaphalis, Arctostaphylos, Arnica, Artemisia, Astragalus, Castilleja, Ceanothus, Centaurea, Chionophila, Chrysopsis, Chrysothamnus, Cichorium, Cirsium, Collinsia, Convolvulus, Corydalis, Dodecatheon, Epilobium, Ericameria, Erigeron, Eriogonum, Erysimum, Eupatorium, Frasera, Geranium, Grindelia, Haplopappus, Helenium, Iris, Linaria, Linum, Lupinus, Melilotus, Mentha, Mertensia, Microseris, Mimulus, Nama, Onosmodium, Orthocarpus, Oxytropis, Pedicularis, Penstemon, Phacelia, Polemonium, Polygonum, Potentilla, Primula, Prunus, Ranunculus, Rhus, Ribes, Rubus, Rudbeckia, Salix, Salvia, Sanicula, Sedum, Senecio, Sisymbrium, Sisyrinchium, Solidago, Sonchus, Symphoricarpos, Symphyotrichum, Tanacetum, Taraxacum, Thermopsis, Trifolium, Vicia and Viguiera (Beattie et al. 1973, Macior 1974, Schmitt 1980, Thorp et al. 1983, Bauer 1983, Mayer et al. 2000, Wilson et al. 2010, Koch et al. 2012, Pyke et al. 2012, Miller-Struttmann and Galen 2014, Williams et al. 2014).

Nests usually built underground, but sometimes on ground surface (Williams et al. 2014). In southern Alberta, 82.4% of 188 nests were built underground. Nests initiated late May to early July, with most begun by mid June; nest entrances often camouflaged (Hobbs 1967, Richards 1978). Mean numbers of eggs, larvae and pupae, respectively, of first broods are 8.7, 8.9 and 8.5. Mean number of eggs laid per cell in second and thirds broods is 3.8. Males patrol circuits in search of queens. Queens apparently mate only once. Queens hibernate in the ground at an average depth of 10.4 cm but up to at least 18 cm. (Hobbs 1967).