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Montana Field Guides

Two-spotted Bumble Bee - Bombus bimaculatus
Other Names:  Pyrobombus bimaculatus


Global Rank: G5
State Rank: SNR

Agency Status
USFWS:
USFS:
BLM:


 

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General Description
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 18-22 mm in length, workers 10-16 mm. Head length medium, cheek just longer than wide; mid leg basitarsus with back far corner rounded, outer surface of hind leg tibia flat and hairless (except fringe) forming pollen basket; hair of face black or with only a few yellow hairs intermixed; upper surface of thorax with dense black spot between wings (often with yellow hairs intermixed), occasionally forming band, sides of thorax yellow; T1 yellow; T2 extensively black at sides of front and always with patch of yellow at mid line, the back edge forming a characteristic "W" shape; T3-5 black. Males 12-15 mm in length; eyes similar in size and shape eyes of any female bumble bee; antennae medium length, flagellum 3X longer than scape; hair color pattern similar to queens and workers, but yellow patch intermixed with black below antennae, T4-5 at sides with at least some yellow (Colla et al. 2011, Williams et al. 2014).

Phenology
Across the range, queens reported February to October, workers March to October, males April to October (Colla et al. 2011, Williams et al. 2014). Earliest queen reported in Boston area by Plath (1934) was 7 April. In southern Ontario, queens reported April to October, workers May to August, males June to October; earliest record 13 April (Colla and Dumesh 2010).

Diagnostic Characteristics
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 outer surface of hind leg tibia concave and hairless (except fringe) forming pollen basket; hair on face predominantly black; cheek longer than wide; T2 with yellow hairs medially and black along sides (the yellow often in shape of "W"), T3 mostly black hairs, T4-6 with black hairs.

Species Range
Resident Year Round

Recorded Montana Distribution

Click the map for additional distribution information.
Distributional Information Provided in Collaboration with the
Montana Entomology Collection at Montana State University
MTEC at MSU

 


Range Comments
East of the Great Plains from extreme southern Canada south to the Gulf Coast (Colla et al. 2011, Williams et al. 2014). Appears to be stable or increasing in abundance throughout its range (Colla and Packer 2008, Grixti et al. 2009, Cameron et al. 2011, Colla et al. 2012, Tripodi and Szalanski 2015), and possibly invading some natural areas previously occupied by Bombus affinus (Molumby and Przybylowicz 2015).

Habitat
In and near oak woodlands, mixed deciduous forest, tallgrass prairie, dunes, farmland, fields and meadows, railroad margins, urban parks and gardens (Snider and Husband 1966, Macior 1968, Hines and Hendrix 2005, Colla and Dumesh 2010, Molumby and Przybylowicz 2012, Williams et al. 2014).
Predicted Suitable Habitat Model

This species has a Predicted Suitable Habit Model available.

To learn how these Models were created see http://mtnhp.org/models

Food Habits
Feeds on a variety of flowers, including Aesculus, Ajuga, Amelanchier, Arabis, Asclepias, Berberis, Campanula, Ceanothus, Cirsium, Cotoneaster, Crataegus, Desmodium, Dicentra, Echinacea, Erythronium, Geranium, Helianthus, Hydrophyllum, Hypericum, Lineria, Lonicera, Lupinus, Mahonia, Melilotus, Medicago, Mertensia, Monarda, Pedicularis Penstemon, Phlox, Polemonium, Prunella, Prunus, Pyrus, Ribes, Rhododendron, Rosa, Rubus, Salix, Solanum, Solidago, Spiraea, Syringa, Taraxacum, Teucrium, Tilia, Trifolium, Vaccinium, Verbena, and Vicea (Plath 1934, Macior 1968, Colla and Dumesh 2010, Colla et al. 2011, Williams et al. 2014, Tripodi and Szalanski 2015).

Reproductive Characteristics
Nests often built underground in rodent nests, sometimes on the ground surface. Plath (1934) reported 37 nests: 2 in stone walls, 9 on the ground surface, 26 underground. Most underground nests were built 15-30 cm below ground, with entrance tunnels 23-122 cm long. Other nests built 122 cm above ground in a stack of wooden crates and under a flat rock on the ground near a stone fence (Snider and Husband 1966). Colonies are relatively small; the largest of the colonies reported by Plath (1934) contained 1 old queen, 23 young queens, about 60 workers, and several cocoons. Newly emerged males share in brood care by incubating pupae during the first 36 hours (Cameron 1985). Males patrol circuits and pursue flying objects in search of queens (Plath 1934, Williams et al. 2014).

References
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Citation for data on this website:
Two-spotted Bumble Bee — Bombus bimaculatus.  Montana Field Guide.  .  Retrieved on , from