One of the cuckoo bumblebees and the most common of the cuckoo species I see here in Manchester.
Bombus vestalis parasitises the nests of Bombus terrestris - buff tailed bumblebees. The female cuckoo bumblebee often emerges a number of weeks later than it’s host and once the early work of a nest is done.
The cuckoo is often similarly marked as the host but larger and with darker wings. When the cuckoo bumblebee finds a nest she wants to take over she will sneak inside and hang around for a few days acquiring the scent of the nest and being accepted by the workers and will then make her move, either dominating or killing the original queen and using her work force to rear her own young.
Cuckoo bumblebees may sound like bad news for social bumblebees but the situation is more subtle than that. Although a cuckoo bumblebee can be bad news for an individual colony of its host species, it is, however, a clear sign that the host population overall is strong and healthy. Cuckoo bumblebees are generally much rarer than their hosts.