Montana Field Guide

For definitions and diagrams of bumble bee morphology please see the Montana State Entomology Collection's Bumble Bee Morphology page. [Former B. californicus now considered this species.] A long-tongued, medium-sized bumble bee: queens 18-21 mm in length, workers 11-17 mm. Head long, cheek distinctly longer than wide; mid-leg basitarsus with far back corner narrowly extended as a spine, outer surface of hind-leg tibia smooth and hairless (except fringe) forming pollen basket; hair on face black or predominantly so; upper side of thorax with black band between wings often narrow and sometimes intermixed with yellow hairs or lacking black hairs entirely, sides of thorax yellow at least in upper half; T1-4 predominantly yellow, T5 black. Males 13-16 mm in length; eyes similar in size and shape to eyes of any female bumble bee; antennae long, flagellum 4X the length of scape; hair color pattern similar to queens and workers, but hair of face and top of head black with minority of yellow intermixed (Colla et al. 2011, Koch et al. 2012, Williams et al. 2014)

[Former B. californicus now considered this species.] Across the range, queens and workers reported March to October, males April to November (Williams et al. 2014). In Utah, queens reported April to June, workers April to September, males June to October (Koch et al. 2012); in southern Ontario, queens April to October, workers and males May to October (Colla and Dumesh 2010). In California (former B. californicus now considered this species), queens reported early February to early October, workers early March to late October, males early May to late October (Thorp et al. 1983).

Please see the Montana State Entomology Collection's Key to Female Bumble Bees in Montana. [Former B. californicus now considered this species.] Females told from other Montana Bombus by a combination of the outer surface of hind-leg tibia concave and hairless (except fringe) forming pollen basket; cheek distinctly longer than wide; face predominantly with black hairs; hairs between wing bases completely or predominantly black; T1-4 predominantly yellow, T5-6 black.

[Former B. californicus now considered this species.] Open farmland and fields, tallgrass prairie, urban parks and gardens, urban prairie open spaces, sagebrush steppe, aspen parkland, montane meadows (Macior 1974, Richards 1978, Hines and Hendrix 2005, McFrederick and LeBuhn 2006, Wojcik et al. 2008, Colla and Dumesh 2010, Wilson et al. 2010, Cook et al. 2011, Molumby and Przybylowicz 2012). Also found infrequently in commercial Vaccinium cropland (Ratti et al. 2008).

[Former B. californicus now considered this species.] Feeds on a variety of flowers, including Ajuga, Anaphalis, Astragalus, Balsamorhiza, Calypso, Caragana, Carduus, Castilleja, Centaurea, Chrysothamnus, Cichorium, Cirsium, Cleome, Coronilla, Delphinium, Digitalis, Dipsacus, Echium, Epilobium, Erigeron, Frasera, Gentiana, Geranium, Grindelia, Helianthus, Hydrophyllum, Hypericum, Impatiens, Iris, Kalmia, Lactuca, Lathyrus, Linaria, Lobelia, Lonicera, Lotus, Lupinus, Lythrum, Malus, Medicago, Melilotus, Mentzelia, Monarda, Nepeta, Onobrychis, Onopordum, Oxytropis, Pedicularis, Penstemon, Phacelia, Potentilla, Prenanthes, Prunella, Rhus, Ribes, Robinia, Rosa, Rudbeckia, Salix, Sisyrinchium, Solanum, Solidago, Sonchus, Spiraea, Spiranthes, Stachys, Symphyotrichum, Symphytum, Taraxacum, Thermopsis, Trifolium, Vaccinium, Vicia and Wyethia (Plath 1934, Macior 1968, Beattie et al. 1973, Macior 1974, Heinrich 1976, Ackerman 1981, Thorp et al. 1983, Mayer et al. 2000, Ratti et al. 2008, Colla and Dumesh 2010, Wilson et al. 2010, Colla et al. 2011, Koch et al. 2012, Williams et al. 2014, Miller-Struttmann and Galen 2014, Ogilvie and Thomson 2015). Also rarely commercial Vaccinium (highbush blueberry) in southern British Columbia (Ratti et al. 2008).

[Former B. californicus now considered this species.] Nests often built under ground, on the ground surface, or above ground in deserted rodent nests. Of 49 nests in the Boston area 61.2% were built underground, 32.6% were surface nests, and 6.1% were built above ground in stone walls or the eve of a shed (Plath 1934). Two of three Michigan nests were built in old mouse nests 61 and 183 cm above ground, the third nest was on the ground under a hay bale (Snider and Husband 1966). In southern Alberta, one study (Hobbs 1966a) reported 41.9% of 31 nests were built under ground and 58.1% on the surface. In a second Alberta study in aspen parkland (Richards 1978), 37.3% of 59 nests were built under ground, 33.9% on the ground surface, and 28.8% above the ground. Nests established in late May through June to mid July. Entrances to ground nests are frequently camouflaged; queens sometimes attempt to usurp nests from conspecifics (Richards 1978). First broods sometimes are small. A single egg is laid in each cell, the number of pupae (cocoons) in first broods averages 8-10. It takes an average of 26-28 days for workers to be produced from first broods. In second and third broods, 2-7 eggs are laid per cell (most often 3-4 eggs). Number of cocoons produced can vary widely, from 27 to 287. Workers of later broods become progressively larger, approaching queen size (Hobbs 1966a); workers have an adult life expectancy of 22-34 days (Goldblatt and Fell 1987). Males perch or hover outside nest entrances in search of queens. Queens dig hibernacula in the ground, to about 5 cm in captivity but probably deeper in the wild, and overwinter. This species parasitized by the cuckoo bumble bees Bombus insularis and B. suckleyi (Hobbs 1966a, Williams et al. 2014).