Probably a white tailed bumblebee worker (Bombus lucornum) in meadow buttercup; it is sometimes difficult to tell.
Once a queen bumblebee has found her nest site, laid eggs and hatched the first brood of workers, she no longer goes out foraging and will not leave the nest again.
The much small workers work inside and outside the nest. Some will guard or clean the nest, while others will forage for nectar and pollen from flowers. Some of the nectar will be eaten at the point of collection to fuel the worker, but much of it will be brought back to the colony to feed to other workers and the next batch of offspring.
Picture by DKG
Conservation status: widespread and abundant.