Montana Field Guide

For definitions and diagrams of bumble bee morphology please see the Montana State Entomology Collection's Bumble Bee Morphology page. A medium-tongued, medium sized bumble bee: queens 17-19 mm in length, workers 9-13 mm. Head length medium, cheek very slightly shorter than wide; mid-leg basitarsus with far back corner rounded, outer surface of hind-leg tibia flat and lacking hair (except fringe) forming a pollen basket; hair of face and upper surface of head predominantly black with patches of yellow hair; upper side of thorax with yellow and black hairs intermixed on scutum, but front edge of black band between wings always sharply defined, and extended backwards in the middle in a dark wedge; T1 yellow, T2-3 orange, T4 yellow, T5 black. Males 10-14 mm in length; eyes similar in size and shape of any female bumble bee; antennae medium long, flagellum 2.5-3X the length of scape; hair color pattern similar to queens and workers, but black wedge on upper surface of thorax less obvious (Colla et al. 2011, Williams et al. 2014).

Across the range, queens reported March to September, workers April to October, males July to October (Colla et al. 2011, Williams et al. 2014). In southern Ontario, queens reported April to September, workers May to September, males July to October; earliest record 15 April (Colla and Dumesh 2010). One of the earliest bumble bees to become active in spring in the eastern United States, with an early date of 5 April (Plath 1934)

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 hind-leg outer surface concave and hairless (except fringe) forming pollen basket; cheek as long as wide; face with yellow hairs at least centrally; scutum with yellow and black hairs intermixed, giving a cloudy appearance; scutellum with yellow or pale yellow hairs divided by line or wedge of black hair; T2-3 orange, T5 black, hairs short and even; coxae often with yellow hair.

Near and in woodlands, old fields, irrigated grassland and forested riparian, aspen parkland (Hobbs 1967, Richards 1978, Johnson 1986, Colla and Dumesh 2010).

Feeds on a variety of flowers, including Achillea, Agastache, Apocynum, Aralia, Asclepias, Astragalus, Centaurea, Chrysothamnus, Cirsium, Claytonia, Coronilla, Cynoglossum, Echium, Epilobium, Eriogonum, Erythronium, Eupatorium, Eurybia, Hieracium, Hypericum, Impatiens, Ledum, Linaria, Lythrum, Medicago, Melilotus, Mentha, Monarda, Prunus, Rosa, Rubus, Salix, Solidago, Spiraea, Symphyotrichum, Tanacetum, Taraxacum, Trifolium, Trillium, Vaccinium, Verbascum, Verbena and Vicia (Plath 1934, Heinrich 1976, Johnson 1986, Colla and Dumesh 2010, Colla et al. 2011, Koch et al. 2012, Williams et al. 2014).

Nests most often underground (Williams et al. 2014). In southern Alberta, 84% of 19 nests reported were built underground. Nests initiated in late May to early June (Hobbs 1967, Richards 1978). Plath (1934) reported a nest excavated in September; the nest had an entrance tunnel 183 cm long leading to the nest 61 cm below the ground surface. This nest contained 23 young queens, 16 males, more than 100 workers, and at least 75 queen pupae (cocoons). Number of pupae in first broods in southern Alberta averaged 9.2; number of eggs laid per cell in second and third broods averaged 3.7 (Hobbs 1967). Males patrol circuits in search of queens. Nests sometimes parasitized by the cuckoo bumble bee Bombus insularis (Williams et al. 2014).