Montana Field Guide

For definitions and diagrams of bumble bee morphology please see the Montana State Entomology Collection's Bumble Bee Morphology page. A long-tongued, small-sized bumble bee: queens 16-18 m in length, workers 10-13 mm. Hair length medium to long and uneven. Head long, cheek distinctly longer than wide; mid-leg basitarsus with back far corner rounded, outer surface of hind-leg tibia smooth and hairless (except fringe) forming pollen basket; hair of face and upper side of head pale yellow with many black hairs intermixed giving cloudy appearance; upper side of thorax in front of wing bases with pale yellow hairs usually intermixed with black giving a cloudy appearance, at the back of thorax the pale yellow usually distinct with with predominantly pale hair; T1-2 yellow and often interrupted in middle with black hair especially broad at front (or sometimes without black), T3-4 red or black with yellow at sides, S3-5 predominantly yellow, T5 black sometimes with fringe at back yellow or rarely extensively brownish-yellow. Males 10-14 mm in length; eyes similar in size and shape to eyes of any female bumble bee; antennae medium length, flagellum 2.5-3X length of scape; hair color pattern similar to queens and workers, but upper side of thorax yellow at front (scutum) often with few or no black hairs intermixed at mid-line, sometime with more black often making black band between wings indistinct; yellow band on upper side of thorax at back often with many scattered black hairs intermixed especially near midline; T1-2 yellow, T3-4 almost always with at least a few black hairs intermixed near midline, if T3-4 red then T5 sometimes also red, if T3-4 lack red, then often extensively yellow (Koch et al. 2012, Williams et al. 2014).

Across the range, queens reported March to September, workers May to September, males May to October (Williams et al. 2014). In Utah, queens reported April to October, workers and males May to September (Koch et al. 2012); in California, queens late March to late August, workers late April to late September, males late May to late 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 outer surface of hind-leg tibia concave and hairless (except fringe) forming pollen basket; cheek distinctly longer than wide; face with pale yellow or white hairs, sometimes with black hairs intermixed giving cloudy appearance; T2 and/or T3 with yellow or black hairs, T3-4 orange (or T3-4 black); scutum of thorax (anterior to wing bases) cloudy with black and yellow hairs intermixed.

Grasslands, prairies, riparian woodlands, aspen parkland, montane meadows, above treeline in alpine tundra (Hobbs 1967, Macior 1974, Richards 1978, Bauer 1983, Bowers 1985, Mayer et al. 2000, Kearns and Oliveras 2009, Wilson et al. 2010, Miller-Struttmann and Galen 2014, Williams et al. 2014). Also croplands of commercial Vaccinium fruit (Ratti et al. 2008).

Feeds on a variety of flowers, including Aconitum, Agastache, Allium, Aster, Astragalus, Calypso, Castilleja, Chamerion, Chionophila, Chrysothamnus, Cirsium, Delphinium, Dodecatheon, Epilobium, Erigeron, Eriogonum, Frasera, Gentiana, Geranium, Grindelia, Haplopappus, Helianthella, Helianthus, Iris, Lathyrus, Linaria, Lupinus, Mentha, Mertensia, Microseris, Mimulus, Onosmodium, Oxytropis, Pedicularis, Penstemon, Phacelia, Phlox, Polemonium, Polygonum, Primula, Rhododendron, Ribes, Rudbeckia, Sedum, Senecio, Sisyrinchium, Solidago, Symphoricarpos, Symphyotrichum, Taraxacum, Thermopsis, Trifolium, Vaccinium, Vicia and Viguiera (Beattie et al. 1973, Macior 1974, Schmitt 1980, Ackerman 1981, Bauer 1983, Thorp et al. 1983, Shaw and Taylor 1986, Mayer et al. 2000, Ratti et al. 2008, Wilson et al. 2010, Pyke et al. 2012, Koch et al. 2012, Miller-Struttmann and Galen 2014, Williams et al. 2014, Ogilvie and Thomson 2015). A significant pollinator of commercial highbush blueberry and cranberry (Vaccinium corymbosum and V. macrocarpon) in southern British Columbia (Ratti et al. 2008).

Nests built mostly underground, rarely on the ground surface. Nests are initiated from mid May to early July. In prairie and mountain woodlands of southern Alberta 89.2% of 37 nests were underground, 10.8% on the ground surface and none above ground. In aspen parkland of southern Alberta 87% of 31 nests built below ground, 3.2% on the ground surface, and 12.9% above ground; queens camouflage entrance tunnels to their underground nests with grass or soil (Hobbs 1967, Richards 1978). Average number of eggs, larvae, and pupae in first broods is 8.2, 8.6, and 9.0, respectively; a single egg is laid in each egg cell. The largest colony with later broods contained 204 larvae (cocoons). Males patrol circuits in search of queens. Autumn queens excavate hibernacula in damp ground on steep north or west slopes, where they overwinter. In hibernation cages hibernacula were 3.8-10.2 cm deep; shallower hibernacula were excavated in compacted soil, deeper hibernacula in loose earth (Hobbs 1967). Probably parasitized by the cuckoo bumble bees Bombus fernaldae and B.suckleyi, a known host for B. insularis (Plath 1934, Hobbs 1967, Williams et al. 2014).