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Suckley's Cuckoo Bumble Bee
As a brood parasite, the variable cuckoo bumble bee does not raise its own young; instead, it “tricks” its host species, the western bumble bee, into tending to its eggs and raising its larvae to adulthood. Its name is a reference to cuckoo birds, many of which lay their eggs in the nests of other bird species.
About This Species
Suckley's cuckoo bumble bee is an extremely rare species that hasn’t been documented in Colorado in over a decade. This species is a brood parasite known to use the western bumble bee (Bombus occidentalis, another bumble bee under federal consideration for U.S. Endangered Species Act listing) as its primary host. As a parasitic species, Suckley’s cuckoo bumble bee has lost its ability to collect and store pollen, secrete wax to make nests, and rear its own young. Instead, a female cuckoo bee takes over a host nest, killing the queen and using the nest workers to rear her own young. The conservation of this species is heavily reliant on the success of their host species.
More Information:
Physical Characteristics
A key characteristic of Suckley’s cuckoo bumble bee is the absence of pollen baskets on its hind legs. Because it tricks another species into rearing its young, it does not collect pollen. To defend themselves against the workers and queen of an invaded colony, these bees have larger and stronger mandibles, a sclerotized (i.e. hardened) abdomen and a more powerful stinger. They have a fully black face, a black stripe across the center of the thorax, and yellow on the outer margins of their fourth and fifth abdominal segments.
Range
Historically, Suckley’s cuckoo bumble bee had a broad range across western North America. However, its range has been vastly reduced; it hasn't been documented in Colorado in a decade.
Habitat
Historically, Suckley’s cuckoo bumble bee has lived in grassland and meadow habitats across a wide range of elevations. Prime habitat contains a high abundance and diversity of flowers.
Diet
Like all bumble bees, this species is a generalist forager, visiting a diversity of flowers, depending on what is available on the landscape. Larvae are fed pollen collected by their host species, the western bumble bee. Historical reports document that they feed predominantly on a diversity of species in the families Asteraceae (the daisy family) and Fabaceae (the pea family).
Reproduction
Cuckoo bumble bees are obligate brood parasites, and are not able to rear offspring without their host. Females emerge from hibernation later in the spring, after their host species has begun establishing nests. To usurp an western bumble bee nest, the female cuckoo bumble bee kills the queen and lays her eggs in the nest; she tricks the nest workers into rearing her young with chemical cues that manipulate their behavior. Once the offspring have emerged as adults, they will leave the nest to mate and forage before finding a location to spend the winter.
Threats to Species
As an obligate brood parasite, Suckley’s cuckoo bumble bee faces its own threats, but is also indirectly affected by threats to its host species, the western bumble bee. Commercially managed bees (both bumble bees and European honey bees) pose a significant threat to native bumble bees. Managed bees can drive disease spillover, when a disease jumps from one population to another. Ongoing research demonstrates that honey bees can outcompete native bumble bees for resources and disrupt their natural foraging behavior. Pesticides also pose a threat to the western bumble bee, with both lethal and nonlethal consequences; bees can be exposed both directly through contact and indirectly through contaminated pollen, nectar and soil. Habitat loss is another major threat to Suckley's cuckoo bumble bee, as they require healthy populations of flowers throughout the growing season and access to suitable nest sites. Finally, climate change poses a significant threat to Suckley's cuckoo bumble bee in many ways, affecting the bees directly and indirectly through the ways their habitats will change.
Additional Information
One of the best ways to support this species is to ensure its host species is readily available on the landscape. There are a number of ways to do this: 1) plant native flowers incorporating species that bloom across the entire growing season, 2) avoid the use of pesticides (both herbicides and insecticides), and 3) participate in community science projects like iNaturalist or the Bumble Bee Atlas to help expand our understanding of species distribution and abundance.
If you would like to help CPW understand and protect our state's bumble bees, you can participate in the Mountain States Bumble Bee Atlas. CPW is partnering with the Xerces Society for Invertebrate Conservation to get the Mountain States Atlas off the ground. Learn more here about how to get involved. If you are not able to participate in the Bumble Bee Atlas formally, you can submit photos of bumble bees you spot as one-off observations to the Bumble Bee Watch.