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-sized bumble bee with a medium-long tongue: queens 17-19 mm, workers 8-11 mm. Hair is long; head length medium with cheek as long as wide; mid-leg basitarsus with far back corner rounded; outer surface of the hind-leg tibia flat and lacking hair except at fringe (fringe hairs pale orange), pollen basket present; hair of face black with some short yellow hairs; upper part of thorax anterior to the wings yellow, sides generally yellow (rarely extensively black), a black band between the wing bases; T1 yellow, T2 yellow or mostly so, T3-4 lacking yellow, T5 orange. Males 10-15 mm in length; eye similar in size and shape to that of any female Bombus; antennae of medium length, flagellum 3X length of scape; hair color pattern similar to queens and workers (Koch et al. 2012, Williams et al. 2014).

Across the range, queens reported from April to September, workers and males May to September (Koch et al. 2012, Williams et al. 2014).

Please see the Montana State Entomology Collection's Key to Female Bumble Bees in Montana. Females differ from other Montana Bombus by a combination of outer surface of hind tibia concave and shiny (not hairy), pollen basket present; cheek as long as or slightly longer than wide; scutellum with yellow hairs only or yellow and black intermixed; T2-6 with some yellow and/or orange; scutum in front of wing bases with yellow hairs only.

Generally selects mountain meadows and taiga, ranging to high mountain and Arctic tundra (Hobbs 1967, Macior 1974, Bauer 1983, Norment 1988, Pyke et al. 2012, Williams et al. 2014).

Visits a wide variety of plants, including Achillea, Besseya, Calypso, Cirsium, Epilobium, Frasera, Geranium, Hedysarum, Helenium, Lupinus, Mertensia, Pedicularis, Penstemon, Phacelia, Polygonum, Potentilla, Salix, Sedum, Senecio, Symphoricarpos, Taraxacum, Trifolium and Vaccinium (Beattie et al. 1973, Macior 1974, Schmitt 1980 , Ackerman 1981, Bauer 1983, Norment 1988, Colla et al. 2011, Koch et al. 2012, Pyke et al. 2012, Miller-Struttmann and Galen 2014, Williams et al. 2014).

An early emerging species in southern Alberta, establishing nests < 1830 m elevation from late April and early May to early June, and at sites > 2395 m in mid to late June (Hobbs 1967, Richards 1978). Two Colorado nests were found above 3600 m elevation in alpine tundra (Macior 1974). The majority of Alberta nests established below treeline are built near the forest-meadow ecotone. Nests are built most often underground, but may be established on the ground surface (usually in an old rodent nest). Nest entrances often camouflaged during nest establishment and prior to creation of a brood chamber. Frequent attempts at nest usurpation by conspecifics and other species of Bombus queens likely contributes to this behavior (Hobbs 1967, Richards 1978). Number of eggs, larvae and pupae of first broods in Alberta nests were 8-10, respectively, with 1 egg per cell. Mean number of eggs per cell of second and third broods averages 3. Overwintering queens occupy hibernacula they excavate in the ground at depths of 2.5 to 3.0 cm (Hobbs 1967). Males patrol circuits in search of queens (Williams et al. 2014). Parasitism by cuckoo bumble bees not reported but is likely (see comments in Hobbs 1967).