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 and medium-sized species: queens 18-23 mm, workers 10-16 mm. Head short with cheek distinctly shorter than broad; mid-leg basitarsus with a rounded back far-corner; hind-leg outer surface of tibia flat and without long hair, but with long fringed at sides, forming a pollen basket; with black hair on side of face and upper head (or with only a few yellow hairs intermixed); small black spot between wings, sometimes inconspicuous but dense; entirely yellow on sides of thorax; T1 yellow, T2 yellow in queen but often brown in worker, sometimes extending 3/4 the length of T2 and forming a "W", and usually with black at the back; T3-6 black, although T2-5 of workers rarely with orange. Males 12-18 mm. Eye greatly enlarged (larger than any female bumble bee) and weakly converged in upper part; antennae long, with the flagellum 3X longer than the scape; hair color pattern similar to queens and workers but with T2 usually brownish (Williams et al. 2014).

Across the range, queens and workers reported March to October, males May to October (Koch et al. 2012, Williams et al. 2014). Plath (1934) reported an early record for queens of 13 May, with workers appearing shortly after 1 June and most males and young queens in August. In southern Ontario, queens May to September (earliest record 11 May), workers June to September, males July to October (Colla and Dumesh 2010). In California, queens active late March to early October, workers late April to late September, males late June to early October (Thorp et al. 1983).

Please see the Montana State Entomology Collection's Key to Female Bumble Bees in Montana. A combination of the following should distinguish queens and workers from other Montana Bombus: outer surface of hind tibia concave and shiny (without hair), pollen basket present; T2 with yellow hairs; cheek shorter than wide; hair between wings yellow, sometimes with a small black spot in middle of yellow hairs; T3 black.

Often found in open farmland, fields, urban parks and gardens, and wetlands (Colla and Dumesh 2010, Williams et al. 2014); in foothill grasslands and montane meadows in Colorado (Macior 1974, Kearns and Oliveras 2009). Also in tallgrass prairie patches of the upper Midwest (Hines and Hendrix 2005, Grixti et al. 2009), and sagebrush steppe, Palouse prairie, and montane meadows in southern Washington and southern Idaho (Mayer et al. 2000, Cook et al. 2011).

Feeds on a variety of flowers, including Agastache, Amorpha, Arabis, Asclepias, Astragalus, Balsamorhiza, Berberis, Bidens, Borago, Camassia, Campanula, Caragana, Carduus, Centaurea, Chrysothamnus, Cirsium, Collinsia, Convolvulus, Cornus, Coronilla, Crataegus, Dalea, Delphinium, Dicentra, Dipsacus, Echinacea, Echium, Epilobium, Eupatorium, Frasera, Geranium, Helianthus, Hesperis, Hibiscus, Hydrophyllum, Hypericum, Ipomoea, Iris, Lactuca, Liatris, Linaria, Lobelia, Lonicera, Lotus, Lupinus, Lythrum, Malus, Medicago, Melilotus, Mentha, Mertensia, Monarda, Onopordum, Pediomelum, Penstemon, Petalostemon, Phacelia, Phlox, Polemonium, Prunella, Prunus, Rhus, Robinia, Rosa, Rubus, Rudbeckia, Salix, Scutellaria, Sedum, Sisyrinchium, Solanum, Solidago, Spiraea, Symphoricarpos, Symphyotrichum, Symphytum, Taraxacum, Teucrium, Thermopsis, Tradescantia, Trifolium, Triodanis, Vaccinium, Verbena, Viburnum, Vicia, Viola, Vitis, Wyethia and Zizia (Macior 1968, Macior 1974, Thorp et al. 1983, Mayer et al. 2000, Colla and Dumesh 2010, Colla et al. 2011, Koch et al. 2012, Miller-Struttmann and Galen 2014, Williams et al. 2014, Tripoldi and Szalanski 2015).

Nests predominantly on the surface of the ground (Plath 1934, Williams et al. 2014). Four surface nests were reported by Plath (1934). The first was discovered on 26 July after recent and probable destruction by a skunk. A second nest on 23 June contained a queen, 10 cocoons, and many larvae and eggs. A third nest on 11 July contained about 20 workers, 1 male, and a small quantity of brood. A fourth nest on 12 July (inside a seashore log) contained a queen and about 12 workers. Workers possess a complex division of labor that changes with worker age and colony age, younger workers feeding larvae more in younger colonies, foraging more intensely with each successive cohort, and becoming increasingly aggressive for dominance in egg-laying as the colony becomes too large and the queen and colony reach senescence (Cameron 1989). Males perch on tree trunks and grass stalks, returning repeatedly for several days to the same perches in territories, and chase after moving objects in their search for queens (Alcock and Alcock 1983, O'Neill et al. 1991). Males also share in brood care of nest-mates by incubating pupae during the first few days after they emerge from pupae as adults (Cameron 1985). Nest parasitism by cuckoo bumble bees not reported.