Montana Field Guide

For definitions and diagrams of bumble bee morphology please see the Montana State Entomology Collection's Bumble Bee Morphology page. A short-tongued, small-sized bumble bee: queens 17-18 mm in length, workers 9-13 mm. Hair short and even; head very short, cheek distinctly shorter than wide; mid-leg basitarsus with the back far corner rounded, hind-leg tibia outer surface flat and hairless (except fringe) forming a pollen basket; many color patterns are expressed, but hair of T2 at front and near midline usually yellow, T1 yellow, T3 orange or black or both. Males 11-15 mm in length; eyes slightly enlarged and weakly convergent in the upper part, larger than eyes of any female bumble bee; antennae medium length, flagellum nearly 3X the length of scape; hair color pattern similar to queens and workers, but black band between wings on upper side of thorax intermixed with many yellow hairs (Colla et al. 2011, Koch et al. 2012, Williams et al 2014).

Across the range, queens reported April to October, workers May to September, males June to September (Williams et al. 2014). In southern Ontario, queens reported May to September, workers June to September, males July to September (Colla and Dumesh 2010); in Utah, queens May to July, workers May to September, males July to October (Koch et al. 2012). In California, queens report late February to early October, workers late May to early October, males late June 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 the outer surface of hind-leg concave and lacking hair (except fringe), pollen basket present; T2-3 with red or orange hair, sometimes with yellow intermixed at least in the middle; scutum predominantly yellow or pale yellow; face predominantly with black hair; cheek distinctly shorter than wide.

Often near and in woodlands, urban parks and gardens in the east, also sagebrush steppe, aspen parkland, prairie grassland to alpine tundra, and commercial Vaccinium crops in the west (Macior 1974, Richards 1978, Ratti et al. 2008, Colla and Dumesh 2010, Cook et al. 2011). In sagebrush steppe, this species appears to become more abundant as sagebrush canopy cover declines (Cook et al. 2011).

Feeds on a wide diversity of flowers, including Apocynum, Arctium, Asclepias, Astragalus, Balsamorhiza, Brassica, Calypso, Campanula, Ceanothus, Centaurea, Chrysothamnus, Cichorium, Cirsium, Cleome, Coronilla, Daucus, Dodecatheon, Echium, Epilobium, Erigeron, Erysimum, Eupatorium, Fragaria, Frasera, Geranium, Grindelia, Haplopappus, Helianthus, Heracleum, Hypericum, Iris, Lactuca, Lupinus, Malus, Medicago, Melilotus, Mentha, Mertensia, Monarda, Onosmodium, Oxytropis, Pedicularis, Penstemon, Phacelia, Potentilla, Prunella, Rorippa, Rosa, Rubus, Sisyrinchium, Solidago, Symphyotrichum, Tanacetum, Taraxacum, Thermopsis, Trifolium, Triteleia, Vaccinium, Verbena, Vicia and Viguiera (Macior 1968, Beattie et al. 1973, Macior 1974, Ackerman 1981, Thorp et al. 1983, Mayer et al. 2000, Ratti et al. 2008, Wilson et al. 2010, Colla and Dumesh 2010, Colla et al. 2011, Koch et al. 2012, Miller-Struttmann and Galen 2014, Williams et al. 2014). An important pollinator in southern British Columbia of commercial Vaccinium crops such as highbush blueberry, and cranberry to a lesser extent (Ratti et al. 2008).

Seems to favor nesting underground under some circumstances, but also commonly nests on the ground surface and above ground; (Plath 1934) reported a Vermont nest 2.6 m above ground in the clapboards of a house. When offered a choice between artificial underground and ground nests in the wooded foothills of the Rocky Mountains of southern Alberta, (Hobbs 1965b) documented 54.5% of 99 nests were constructed underground. In aspen parkland of southern Alberta, (Richards 1978) reported that 81.4% of 43 nests in one year and 58.2% of 67 nests the following year were built on the surface or above ground when queens were offered an equal choice of artificial nest sites. Nests initiated late May to mid July, with the majority started in June. Sometimes, conspecific queens attempt to take over established nests (Hobbs 1965b, Richards 1978). In first broods, the average number of eggs = 11.2 (range: 8-15), larvae = 10.2 (range: 7-13), and pupae (cocoons) = 10.4 (range: 7-15). Queens produce workers in 19-24 days after initiating nests. For second and third broods, 3-5 eggs (mean = 4.2) are laid per cell, in fourth and fifth broods 4-13 eggs (mean = 8.2) are laid per cell. Average numbers of cocoons produced in some colonies producing queens were 66-157; the largest colony produced 430 cocoons, at least 33 males, and 103 queens. During winter, queens construct hibernacula and hibernate in the ground at depths of 2.5-6.4 cm (Hobbs 1965b). Males maintain territories often centered on blooming shrubs, frequently changing perches and pursuing passing insects and birds in search of queens (O'Neill et al. 1991). Some nests are parasitized by the cuckoo bumble bees Bombus suckleyi, B. insularis, and B. flavidus (=fernaldae) (Hobbs 1965b).