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 large bee: queen 21-23 mm, worker 9-14 mm. Hair short and even; head length medium with as long as broad or just shorter than broad; mid-leg basitarsus back far corner rounded, outer surface of hind-leg tibia flat and without long hair but with long fringes at sided forming a pollen basket; hair of the face black or with a few yellow hairs; thorax mostly yellow, with a large patch between the wings intermixed with black hairs; T1 yellow, T2 usually entirely black, T3-6 black. Male 12-14 mm; eye similar in size to any female bumble bee; antennae medium length with flagelum 3X longer than scape; hair color similar to queens and workers, but with a yellow patch below the antennae and many yellow hairs on underside of segments 2-6 of abdomen (Colla et al. 2011, Williams et al. 2014).

Emerges in early spring. Queens active April to October, workers May to November, males June to November (Colla et al. 2011, Williams et al. 2014). In southern Ontario, the earliest record 23 April, queens active April to October, workers May to October, males June to October (Colla and Dumesh 2010); in the Boston Massachusetts area, queens emerge from hibernacula starting 15 April, workers appear in early June, the majority of young queens and males in August and September (Plath 1934).

Please see the Montana State Entomology Collection's Key to Female Bumble Bees in Montana. Females distinguished from other Montana Bombus by a combination of concave and shiny outer surface of hind-leg tibia with pollen basket present; cheek slightly longer than wide; T1 yellow, T2-6 black; scutellum yellow only or intermixed with black throughout.

In or near woodlands, grasslands, farmlands, wetlands, urban parks and gardens (Matteson and Langellotto 2009, Colla and Dumesh 2010, Williams et al. 2014). Also uses tallgrass prairie patches in the upper Midwest (Hines and Hendrix 2005).

Recorded from more than 75 species of flowers, including Agastache, Amelanchier, Aquilegia, Arabis, Arctium, Asclepias, Berberis, Bidens, Camassia, Campanula, Caragana, Carduus, Ceanothus, Centaurea, Cicuta, Cirsium, Claytonia, Clematis, Collinsia, Coreopsis, Crataegus, Dalea, Daucus, Delphinium, Echinacea, Echium, Epilobium, Erythronium, Eupatorium, Fragaria, Gaura, Geranium, Helenium, Helianthus, Hesperis, Hydrophyllum, Hypericum, Impatiens, Kalmia, Lactuca, Liatris, Lithospermum, Lonicera, Lupinus, Lycopus, Lythrum, Malus, Medicago, Melilotus, Mentha, Monarda, Nepeta, Oenothera, Onopordum, Osmorhiza, Pediomelum, Penstemon, Philadelphus, Phlox, Polemonium, Potentilla, Prenanthes, Prunella, Prunus, Rhododendron, Rhus, Ribes, Rosa, Rubus, Rudbeckia, Salix, Salvia, Scrophularia, Scutellaria, Silene, Solanum, Solidago, Spiraea, Stachys, Symphoricarpos, Symphyotrichum, Symphytum, Taraxacum, Trifolium, Vaccinium, Verbena, Vicia and Viola (Plath 1934, Macior 1968, MacKenzie and Averill 1995, Stubbs and Drummond 2001, Ratti et al. 2008, Colla and Dumesh 2010, Colla et al. 2011, Williams et al. 2014, Tripoldi and Szalanski 2015). Used to pollinate commercial blueberry (Vaccinium) field crops as well as a variety of greenhouse vegetables, such as tomatoes, muskmelons, and sweet peppers (Stubbs and Drummond 2001, Matteson and Langellotto 2009).

Nests underground. Plath (1934) reported 80 nests during the years 1921-1933, all of which were subterranean, located at depths of 30-90 cm, and with entrance tunnels extending 45-271 cm. In southern Ontario queens dig hibernacula from late September through October at depths of 3 to 15 cm, sometimes hibernating as pairs, more often singly; spring emergence occurred from early April throughout May, with peak emergence in late April (Szabo and Pengelly 1973). Nest are quite large, with one Massachusetts nest in early August containing 1 dead queen, 450 workers, and a large quantity of brood, which included at least 500 male and queen cocoons (Plath 1934); an Ontario nest excavated in late October contained 16 queens and a brood comb containing 1357 small cocoons and 674 larger cocoons (Szabo and Pengelly 1973). Number of queens and males per colony can be relatively small (mean for each in 11 captive colonies = 9, range: 0-69), but colonies contain a large number of workers (mean in 11 colonies = 375, range: 186-540)(Cnaani et al. 2002).

Eggs of all castes produce larvae in 5 days, queens remain as larve for about 18 days, 9-10 days for workers and males; the pupal stage lasts about 14 days for queens, 10-11 days for workers and males. Workers are capable of laying eggs and rearing larvae to adulthood in colonies that are two months old (Cnaani et al. 2002). Worker size can vary ten-fold, with smaller workers better able to resist starvation, which may help colonies persist through times of nectar shortage (Couvillon and Dornhaus2010). Nests are parasitized by the cuckoo bumble bee Bombus citrinus; 14.3% of 49 nests in the Boston area were parasitized by this species (Plath 1934, Colla et al. 2011, Williams et al. 2014). However, experimental evidence shows that B. impatiens is probably a secondary host for B. citrinus, given the relatively low success rate of invading nests of this host species compared to the primary host, B. vagans (Fisher 1985).