Suckley’s cuckoo bumble bee females are 1.8 to 2.3 cm in length. Cuckoo bumble bees,including Suckley’s cuckoo bumble bee, do not have a pollen carrying basket (corbicula) on their hind leg, unlike the true bumble bees. Instead, their hind leg tibia is convex and densely covered in hairs. Their hair is short and even. The hair of the head (including the vertex – top of the head) is black. The hair of the thorax (including below the wings) is mostly yellow, with a black spot or band between the wings, sometimes with a black triangular notch behind, and between the wings. The first two tergal segments on the abdomen are black, usually with at least some yellow on T3 – no yellow centrally. T4 has predominantly yellow hairs, with a patch of black centrally and anteriorly. T5 is usually black but can have yellow laterally; T6 is black. The tip of the abdomen is recurved ventrally, with two strong triangular ridges visible in dorsal view. The male is 13 to 16 mm in length. The color patterns for males are extremely variable. The only consistent features are yellow on all of T1 and T4, with some (or all) yellow on T2, T3, T5 and T6. T7 is black.
Bombus suckleyi need another Bombus spp. to serve as a host colony. Because they have no corbicula, they have an obligate dependency on other bumble bees to collect pollen on which to rear their young. They are nest parasites of other species of bumble bees and have been documented breeding as a parasite of colonies of Bombus occidentalis, and has been recorded as present in the colonies of B. terricola, B. rufocinctus, B. fervidus, B. nevadensis, and B. appositus. While females do not collect pollen to return to the nest, both adult males and females of this species forage for pollen and nectar from flowers for their own nutritional and energetic needs. The adult food plants of this species include Aster sp., Chrysothamnus sp., Cirsium sp., and Solidago sp.. There are also several records of this species visiting Centaurea repens. They are likely to be found with their bumble bee hosts in flower-rich meadows of forests and subalpine zones.
Limiting factors
Cuckoo bumble bees are obligate social parasites and thus any change to resources available to or stressor effects on the host will be reflected in the status of the parasite. Signs that host species are declining are of major concern to the viability of Suckley’s cuckoo bumble bee. Additional direct threats that may be impacting this species include pesticide use, habitat loss, pathogens from managed pollinators, competition with non-native bees, and changes in temperature related to climate change. Bumble bee species require temperatures to be within a suitable range, bounded by upper (heat) and lower (cold) thermal limits. Reduced genetic diversity resulting from any of these threats can be particularly concerning for bumble bees, since their method of sex-determination can be disrupted by inbreeding.
Data gaps
Collect life history information. Confirm successful reproduction in suspected hosts other than B. occidentalis. Document overwintering habitat preferences and important host plants. Obtain current population size and trend data. Assess distribution and determine range. Assess population genetics and develop eDNA sampling protocols.
Conservation actions
Monitor existing populations and habitat. Conduct targeted Bombus sp. surveys, especially at higher elevations. Manage habitat to provide preferred nectar and pollen plant species. Protect new and known occupied sites.
Key reference or plan
U.S. Fish and Wildlife Service. 2024. Species status assessment report for the Suckley’s Cuckoo Bumble Bee (Bombus suckleyi), Version 1.0. August 2024. Alaska Region. 131 pp.
Hamon, L., R. Hatfield, S. Jepsen, and S. Foltz Jordan. 2024. Interagency Special Status/Sensitive Species Program (ISSSSP) Species Fact Sheet: Bombus suckleyi. USDA Forest Service Region 6 and USDI Bureau of Land Management Oregon State Office. 26 pp.
