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Montana Animal Field Guide

Montana Field Guides

Sitka Bumble Bee - Bombus sitkensis
Other Names:  Pyrobombus sitkensis


Global Rank: G4G5
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, small-sized bumble bee: queens 15-20 mm in length, workers 9-14 mm. Hair long, shaggy, uneven; head length medium, cheek as long as wide; mid-leg basitarsus with back far corner rounded, hind-leg tibia outer surface flat and hairless (except fringe) forming pollen basket; hair on upper surface of thorax yellow but densely intermixed with black especially between wings and on scutellum; T1 yellow, T2 with yellow often narrowly interrupted by black especially at back or intermixed with black, T5 almost entirely pale brownish yellow (yellow and orange hairs intermixed). Males 9-14 mm in length; eyes similar in size and shape to eyes of any female Bombus; antennae medium length, flagellum 3X longer than scape; hair color pattern similar to queens and workers, but upper side of thorax with more yellow hair intermixed with black between wings; T3 usually with pale fringe of yellow hair at back or entirely yellow (Koch et al. 2012, Williams et al. 2014).

Phenology
Across the range, queens reported March to September, workers April to September, males April to October (Williams et al. 2014). In Washington, queens reported March to August, workers May to October, males April to October (Koch et al. 2012); in California, queens late January to early December, workers early March to late September, males early April to early September (Thorp et al. 1983).

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 hind-leg tibia outer surface concave and hairless (except fringe) forming a pollen basket; T1-2 and T4-5 with yellow and/or orange hairs; cheek as long or slightly longer than wide; scutum cloudy (yellow and black hairs intermixed); scutellum distinctly darker than scutum (many black hairs intermixed throughout).

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
Along the Pacific Coast from southern Alaska to central California in the Cascade Mountains and Coast Ranges, and inland in the Rocky Mountains from central British Columbia and Alberta south through northern Idaho, western Montana, to extreme northwestern Wyoming (Koch at al. 2012, Williams et al. 2014). Some possible declines in urban range due to competition with Bombus vosnesenskii (McFrederick and LeBuhn 2006).

Habitat
Open grassy prairie, montane meadows, urban gardens and parks, commercial blueberry and cranberry cropland (McFrederick and LeBuhn 2006, Ratti et al. 2008, Wojcik et al. 2008, 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 Aquilegia, Brassica, Ceanothus, Cirsium, Epilobium, Lupinus, Phacelia, Rhododendron, Ribes, Rosa, Rubus, Salix, Solidago, Vaccinium and Vicea (Thorp et al. 1983, Wilson et al. 2010, Koch et al. 2012, Williams et al. 2014). A minor pollinator in crops of commercial Vaccinium (highbush blueberry and cranberry) in southern British Columbia (Ratti et al. 2008).

Reproductive Characteristics
Little information. Nests built underground, presumably in rodent burrows (McFrederick and LeBuhn 2006). Males patrol circuits in search of queens (Williams et al. 2014).

References
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Citation for data on this website:
Sitka Bumble Bee — Bombus sitkensis.  Montana Field Guide.  .  Retrieved on , from