Cuckoo bumble bees (Bombus insularis & flavidus)
Cuckoo bumble bees (Bombus insularis & flavidus)
Cuckoo bumble bees are less frequently encountered than other bumble bees because they do not have their own workers. I may find a few individuals in my yard each year.
A female cuckoo bumble bee invades an established nest of a host species, kills the queen, and uses the host's workers to raise her offspring. Neither females nor males collect pollen.
Two species are known to occur in the Pacific Northwest: the indiscriminate cuckoo bumble bee (Bombus insularis) and the Fernald cuckoo bumble bee (Bombus flavidus, also known as Bombus fernaldae). While they closely resemble each other, individuals found in lowland areas are likely B. insularis.
For a more detailed comparison, refer to Bumble Bees of the Western United States—the indiscriminate cuckoo bumble bee is covered on page 126, and the Fernald cuckoo bumble bee (listed as Bombus fernaldae) on page 130.
These photos were taken in my immediate neighborhood. Since it is a residential area in the lowlands, the bees are likely indiscriminate cuckoo bumble bees (B.insularis).
This individual was found in the foothills of the Cascade Range (1,000 ft). It might be the Fernald cuckoo bumble bee (Bombus flavidus), as it appears more slender than Bombus insularis.