Urban Pollinators: Invasion of the bee snatchers

Southern cuckoo bumblebee (Bombus vestalis)

If you think there are only the hard-working bumblebees, busily collecting pollen and nectar all day, rearing their young and sacrificing themself for the well-being of their colony then read on as there is another bumblebee around, lazily sipping nectar all day and enslaving the workers of the hard-working bumblebees to rear their offspring.

These other bumblebees are aptly named cuckoo bumblebees and there are six species in the UK. All cuckoo bumblebee species resemble their host bumblebee species in appearance with often the same or a very similar colour pattern as the host species.

The most common species of cuckoo bumblebee in southern and central England is the Southern cuckoo bee (Bombus vestalis). It`s host bumblebee species is the buff-tailed bumblebee (Bombus terrestris). Southern cuckoo bees are often found in gardens, parks and woodlands.

Host species of Bombus vestalis: Buff-tailed bumblebee (B. terrestris)

Cuckoo bumblebees often emerge quite late in spring when ordinary bumblebees have already established their colonies. They also have no caste system with queen, worker and males as in ordinary bumblebees but only have females and males. There are important differences between cuckoo bumblebees and ordinary bumblebees, some of them can help you to distinguish between the two types of bumblebee.

1. Cuckoo bumblebees have no pollen baskets on the rear legs and you will never see a cuckoo bumblebee loaded with pollen on the hind legs.
2. They have also shortish tongues and are less hairy than ordinary bumblebees
3. The body is much harder than the body of ordinary bumblebees which gives them an advantage in fights when taking over a bumblebee colony
4. The wings are often dusky or dark in colour

A cuckoo bumblebee, good to see is the harder, less-hairy body

Cuckoo bumblebee searching for a bumblebee colony

It is thought that female cuckoo bumblebees find the host bumblebee colony by smell. They go into the colony and kill or subdue the queen and start laying their eggs. The workers are enslaved with pheromones and/or physical attacks and will rear the young of the cuckoo bumblebee now instead of the young of their queen. After the new generation of cuckoo bumblebees emerge they will leave the nest for mating and the females try to find new colonies to attack.

As cuckoo bumblebees only have to provide for themselves they seem to have a lot of time to just hang around and lazily sipping nectar from flowers now and again. They will never fly industriously from flower to flower as ordinary bumblebee workers will do on a sunny day.