Montana Field Guide

For definitions and diagrams of bumble bee morphology please see the Montana State Entomology Collection's Bumble Bee Morphology page. Medium sized and short-tongued: queens 18-23 mm (no workers). Outer surface of hind-leg tibia convex and densely hairy, lacks a pollen basket. Hair short and even, black on the face, predominantly yellow on sides of the thorax, black continuously along midline to anterior region of T4. Males 13-16 mm, hair color on sides of thorax yellow, T2 extensively yellow, T4 mostly yellow sometimes with narrow area of black hairs along midline, T7 black, antenna medium length, flagellum 3x longer than the scape (Williams et al. 2014).

Queens reported April through August, males June through October (Koch et al. 2012, Williams et al 2014). In California, queens reported late May to late October, males early July to late September (Thorp et al. 1983).

Please see the Montana State Entomology Collection's Key to Female Bumble Bees in Montana. Outer surface of the hind tibia convex, densely hairy and lacking a pollen basket separates B. suckleyi from other Bombus except other cuckoo bumble bees. Predominantly black occiput separates B. suckleyi from other western cuckoo bumble bees, which have predominantly yellow hairs covering the occiput (Koch et al. 2012).

Reported in grassland and shrub-steppe along the Snake River Plain of southeastern Washington, and in conifer forest uplands nearby (Mayer et al. 2000). In the Lower Fraser Valley of British Columbia, they were not detected in commercial berry (Vaccinium, Rhubus) fields, instead preferring native vegetation, and found in greater numbers as distance from commercial operations increased (MacKenzie and Winston 1984). Present in montane to subalpine mesic and wet meadows in Colorado (Macior 1974).

Do not intentionally gather pollen but may transport it (Beattie et al. 1973). Instead B. suckleyi parasitize nests of other bumble bees. Food plants include "asters", Agastache, Centaurea, Chrysothamnus, Cirsium, Epilobium, Erysimum, Frasera, Haplopappus, Iris, Melilotus, Penstemon, Salix, Senecio, Sisyrinchium, Solidago, Symphyotrichum, Taraxacum, Trifolium and Triteleia (Beattie et al. 1973, Macior 1974, Thorp et al. 1983, Mayer et al. 2000, Koch et al. 2012, Miller-Struttmann and Galen 2014).

A social parasite, killing the host and nesting in colonies of other bumble bees, especially B. occidentalis, but recorded from colonies of B. terricola, B. rufocinctus, B. fervidus, B. nevadensis, and B. appositus (Hobbs 1965a and b, Hobbs 1966a and b, Williams 2014). In one southern Alberta study, reported to have depredated 80% of 15 B. occidentalis nests (Hobbs 1968). Males patrol circuits in search of queens (Williams et al. 2014). Apparent declines in B. suckleyi may be tied to declines in their primary host species (B. occidentalis).

Suckley Cuckoo Bumble Bee has been listed on the IUCN Redlist as Critically Endangered due to a decreasing population trend and habitat based threats (Hatfield et al. 2015). In April 2020, the species was petitioned for listing under the Endangered Species Act. On December 17th, 2024 the US Fish and Wildlife Service proposed listing the species as Endangered under the ESA. Due to the current lack of data sufficient to perform required analyses, they conclude that the designation of critical habitat for the species Was not determinable at this time.

For information on the federal status of the species, Please visit the U.S. Fish and Wildlife Service's Suckley's Cuckoo Bumble Bee Page.