Psithyrus
Guides
Bombus ashtoni
Ashton's cuckoo bumble bee
Bombus ashtoni is a cuckoo bumble bee (subgenus Psithyrus) native to North America. Unlike social bumble bees, this species does not produce workers or construct its own nests. Instead, females infiltrate established colonies of other Bombus species and exploit the host workers to rear their own offspring. This parasitic lifestyle has been documented specifically with hosts including Bombus affinis, Bombus terricola, and Bombus fervidus. The species is subject to the same conservation concerns affecting its host species, particularly the endangered rusty patched bumble bee (B. affinis).
Bombus citrinus
lemon cuckoo bumblebee
Bombus citrinus is a cuckoo bumblebee native to eastern North America, recognized by its lemon-yellow coloration. As an obligate social parasite, it invades colonies of other bumblebees, kills the resident queen, and assumes control of the host worker population. It belongs to the subgenus Psithyrus, a group of parasitic bumblebees that have lost the ability to collect pollen and rear their own workers.
Bombus insularis
Indiscriminate Cuckoo Bumble Bee
Bombus insularis is a cuckoo bumble bee in the subgenus Psithyrus, native to northern and western North America. As a social parasite, it invades nests of host bumble bee species, usurps the resident queen, and exploits host workers to rear its own offspring. The species is known for its broad host range, attacking multiple bumble bee species across diverse habitats including tundra, taiga, and mountain ranges.
Bombus suckleyi
Suckley's Cuckoo Bumble Bee, Suckley's Bumble Bee
Bombus suckleyi is a cuckoo bumble bee (subgenus Psithyrus) and obligate social parasite of other Bombus species. It lacks corbiculae (pollen baskets) on its hind legs, having lost the ability to collect pollen and nectar for its own brood. The species invades host colonies, kills or subdues the resident queen, and manipulates host workers to provision its offspring. Native to northwestern North America, it has experienced severe population declines of approximately 77% and is classified as critically endangered by the IUCN and NatureServe.
Bombus variabilis
Variable Cuckoo Bumble Bee, Variable Cuckoo Bumblebee
Bombus variabilis is a parasitic bumble bee (subgenus Psithyrus) native to North America. It lacks the ability to collect pollen or establish its own colonies, instead infiltrating nests of host bumble bees to reproduce. The species is critically dependent on Bombus pensylvanicus as its primary host, making its survival tightly linked to host population trends. Bombus variabilis has experienced significant decline due to habitat loss and climate change affecting its host.