Montana Field Guide

For definitions and diagrams of bumble bee morphology please see the Montana State Entomology Collection's Bumble Bee Morphology page. Large sized and long-tongued: queens 22-26 mm, workers 13-19 mm. face long with cheek slightly longer than broad, clypeus with large pits or punctures except on midline; hind-leg tibia flat on outer surface and lacking long hair, but with long fringe on sides forming a pollen basket, mid-leg basitarsus with back far corner narrowly extended as a spine. Hair short and even; hair black usually between bases of wings, hair of face and upperside of head black, sides of thorax black, T1 with yellow hairs dominant at midline, T2-3 yellow, T4 black. Males 15-21 mm, hair color pattern similar to queens and workers but T7 often orange (or if black then T2-3 entirely yellow), antenna long, flagellum 4x longer than the scape (Colla et al. 2011, Williams et al. 2014).

Queens and workers reported March to November, males April to November (Williams et al. 2014). In southern Ontario the earliest record is 15 May, with queens and workers to September, males July to October (Colla and Dumesh 2010, Colla et al. 2011). Considered a late-emerging species in the East and Midwest (Plath 1934, Grixti et al. 2009).

Please see the Montana State Entomology Collection's Key to Female Bumble Bees in Montana. Combination of hair of face black, hair on sides of thorax mostly black, clypeus pitted along midline, T2 yellow, spine on proximal portion of basitarsus of hind-leg and distal posterior corner of basitarsus of mid-leg, and presence of pollen basket help distinguish females of this species from other Bombus. T1 with yellow hairs (at least at midline), and clypeus rough and pitted or punctured in middle separate this species from B. auricomus.

Open farmlands and fields, tallgrass and other prairie patches (Johnson 1986, Hines and Hendrix 2005, Colla and Dumesh 2010).

Feeds on a wide variety of flowers; more than 95 species reported in Ontario. Species include Amelanchier, Amorpha, Antennaria, Asclepias, Astragalus, Campanula, Carduus, Cerastium, Cirsium, Claytonia, Clematis, Collinsia, Cornus, Crataegus, Dalea, Delphinium, Dipsacus, Dodecatheon, Echinacea, Eupatorium, Gaura, Gentiana, Geranium, Helianthus, Hesperis, Heuchera, Hibiscus, Hypericum, Ipomoea, Iris, Kalmia, Liatris, Lithospermum, Lobelia, Lonicera, Lotus, Lupinus, Malus, Medicago, Mentzelia, Mertensia, Mimulus, Monarda, Oenothera, Orobanche, Oxalis, Pediomelum, Penstemon, Phlox, Plantago, Polygonum, Potentilla, Prunus, Rhamnus, Ribes, Robinia, Rubus, Rudbeckia, Sagittaria, Salix, Salvia, Silene, Solanum, Solidago, Stachys, Symphoricarpos, Symphyotrichum, Taraxacum, Tradescantia, Trifolium, Triodanis, Vaccinium, Verbascum, Verbena, Veronica, Viburnum, Vicia, Viola and Zizia (Macior 1968, Johnson 1986, Colla and Dumesh 2010, Colla et al. 2011, Williams et al. 2014, Tripoldi and Szalanski 2015).

Nests mostly on the surface of the ground among long grass, less often to 15 cm below ground (Plath 1934, Williams et al, 2014). A late July nest in New England contained a queen plus 37 workers and a considerable quantity of brood; two Virginia colonies in early July contained a queen with 6 workers, and a queen with 12 workers. Workers (3 cohorts) live for 23 to 35 days, with the shortest-lived those from the latest cohort (Plath 1934, Goldblatt and Fell 1987). Males congregate around nest entrances in search of mates. Parasitized in the East and Midwest by queens of Bombus variabilis and Bombus insularis, who kill the queens of B. pensylvanicus and engage the workers to raise the B. variabilis and B. insularis broods (Plath 1934, Colla et al. 2011, Williams et al. 2014).