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Montana Field Guides

Indiscriminate Cuckoo Bumble Bee - Bombus insularis
Other Names:  Psithyrus insularis

Native Species

Global Rank: G3
State Rank: SNR

Agency Status


External Links

General Description
For definitions and diagrams of bumble bee morphology please see the Montana State Entomology Collection's Bumble Bee Morphology page. Medium-sized: queens (no workers) 16-20 mm in length. Hair length medium; outer surface of hind-leg tibia flat, densely hairy, and lacks pollen basket; hair of face black with a dense yellow patch above base of antennae; sides of thorax yellow at front and black on underside and rear; upperside of thorax with black band between the wings extending back between yellow along midline; T1-2 black or mostly so, T3 black or with some yellow along sides but always black along midline, T4-5 extensively yellow at sides; wings light brown. Male 11-16 mm in length; eyes similar in size and shape to eyes of any female bumble bee; antennae medium length, flagellum 3X the length of scape; hair of face black, with any yellow hairs above base of antennae; upperside of head (occiput) yellow or with many yellow hairs intermixed; T4 with many yellow hairs at sides but a distinct black patch along midline; T7 black; hair length of T3 at front and middle longer than hind-leg basitarsus breadth (Colla et al. 2011, Koch et al. 2012, Williams et al. 2014).

Across the range, queens reported April to September, males May to September; no workers (Williams et al 2014). Queens May to August, males July to September in southern Ontario (Colla and Dumesh 2010, Colla et al. 2011); queens March to September, males July to September in Utah (Koch et al. 2012); queens late March to late October, males late April to late September in California (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 the outer surface of the the hind-leg tibia convex and hairy, no pollen basket present; top of head (occiput) predominantly of yellow hairs; hairs of face predominantly yellow around antennae bases; S6 with evenly rounded side ridges.

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


Range Comments
In western North America from Alaska south through the Cascade, Sierra Nevada, and Rocky Mountains west of the Great Plains to southern California, Arizona, and New Mexico, and east across southern Canada to New England and southern Quebec (Colla et al. 2011, Koch et al. 2012, Williams et al. 2014). In Colorado, found at elevations of 1600-4000 m, but mostly between 2400-3000 m (Macior 1974); at least 1600-3000 m elevation in California (Thorp et al. 1983). In Montana, reaches at least 3050 m elevation in the Beartooth Mountains (Bauer 1983). Evidence of declines in parts of its range, possibly because of declines in host bumble bee populations (Colla et al. 2012, Williams et al. 2014).

Found in a wide variety of habitats, including native prairie, sagebrush steppe, montane and subalpine meadows, alpine tundra (Macior 1974, Bauer 1983, Mayer et al. 2000, Wilson et al. 2010, Cook et al. 2011, Miller-Struttmann and Galen 2014).
Predicted Suitable Habitat Model

This species has a Predicted Suitable Habitat Model available.

To learn how these Models were created see

Food Habits
Does not collect pollen, but feeds on a variety of flowers, including Achillea, Agastache, Agoseris, Anaphalis, Arctostaphylos, Asclepias, Astragalus, Barbarea, Besseya, Centaurea, Chrysothamnus, Cirsium, Corydalis, Dipsacus, Epilobium, Erigeron, Eriogonum, Erysimum, Eupatorium, Frasera, Haplopappus, Helenium, Helianthus, Iris, Malus, Melilotus, Mentha, Mertensia, Microseris, Onosmodium, Oxytropis, Penstemon, Phacelia, Polygonum, Primula, Rhododendron, Rhus, Ribes, Rubus, Sedum, Senecio, Smelowskia, Solidago, Symphyotrichum, Taraxacum, Trifolium, Vaccinium, Veratrum, Vicia, Viguiera and Wyethia (Beattie et al. 1973, Macior 1974, Bauer 1983, Thorp et al. 1983, Mayer et al. 2000, Ratti et al. 2008, Wilson et al. 2010, Colla and Dumesh 2010, Colla et al. 2011, Koch et al. 2012, Williams et al. 2014, Miller-Struttmann and Galen 2014).

Reproductive Characteristics
A social parasite of other Bombus, including B. appositus, B. fervidus, B. flavifrons, B. nevadensis, B. occidentalis, B. rufocinctus, B. ternarius, and B. terricola (Hobbs 1965a and b, 1966a and b, 1968; Williams et al. 2014). Parasitic queens invade hosts nests, sometimes kill the host queen, and recruit host workers to raise parasite progeny. This is necessary because parasite queens do not gather pollen required to fed their own larvae. Host workers sometimes defend against parasite queens by covering them in honey. As many as 12 parasite eggs are laid per cell; eggs produce only queens and males. Males patrol circuits in search of queens.

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Citation for data on this website:
Indiscriminate Cuckoo Bumble Bee — Bombus insularis.  Montana Field Guide.  .  Retrieved on , from