What is a Cuckoo bumble bee?
To paraphrase Bumble Bees and Cuckoo Bumble Bees of California by Thorp, Horning, Jr and Dunning: Cuckoo bumble bees are social parasites without worker castes which usurp bumble bee nests and propagate themselves at the expense of their bumble bee hosts.
In other words, a queen cuckoo waits until another bumble bee species has an active nest with lots of workers. She invades the nest and kills the original queen. She then has the workers of the dead queen raise her eggs and larvae, rather than eggs and larvae of their own species. This has similarities to a cuckoo bird, which lays eggs in other birds’ nests.
Cuckoo bumble bees are the tanks of the bumble world: heavily armored and ready for conquest. Cuckoo queens lack a corbiculum (pollen basket) as they never gather pollen to take back to “their” nest.
Queens of non-cuckoo bumble bees collect pollen to feed their first set of workers each spring–so they need a corbiculum to collect and bring home pollen with which to raise the first set of workers. After the first set of workers hatch, the queen stays in the nest laying eggs while the workers go out foraging.
Cuckoos wait until other queens have established a nest with multiple generations of workers before they invade the colony, kill the existing queen and convince the workers to raise cuckoo bumble bee offspring.
Having said that, cuckoo bumbles are cool and part of the ecosystem.
They are a treat to encounter in the field.
Species are not bad or good.
Biodiversity is good.
Recognizing a cuckoo when we see it
If you see an unfamiliar bumble bee (cuckoos are rare relative to most other species in a given area) that seems very deliberate in its movements and walks from flower to flower, look closely at it’s rearmost legs. Is there a corbiculum present? Pollen basket?
If there isn’t then look closer. If no corbiculum, is it heavily armored? Behaviorally I (DJ) have noticed that, as a class, cuckoos often resist flying. They can fly, and do, but when they are on wildflowers they often walk from flower to flower rather than buzz from one to another as non-cuckoos do.
This may be due to the heavier weight of their thick exoskeleton. Because they are raised as warriors to go in and take over existing colonies, including killing the queen and any workers that rise to her defense, they are built much sturdier than non-cuckoos. It may take a lot more energy to fly around therefore more energy efficient to walk.
Cuckoo bumble species in Washington state include:
- Indiscriminate bumble bee, B. insularis
- Fernald cuckoo bumble, B. flavidus/fernaldae
- Suckley cuckoo bumble, B suckleyi
No pictures of Suckley bumble, B suckleyi available.