Buff-tailed bumblebees (Bombus terrestris) have a yellow-brown bottom (faintly so in the case of workers) which differentiates them from other species such as white-tailed bumblebees (Bombus lucorum).
These bees are social insects who nest in colonies of 100-500 in empty mouse nests or along longer tunnels. A solitary queen mates with a male and finds a nest to overwinter. In spring she lays eggs and tends the larvae which pupate into female workers. Workers forage for nectar and pollen for later generations of larvae, some of which develop into male drones and some of which receive extra food and pupate to become new queens. The colony persists until autumn when young queens leave the nest, mate and find a hibernation site.
Bumblebees and honey bees have a preference for blue and yellow flowers. Recent research shows that exposure to neonicotinoid pesticides causes impairment of the bumblebees’ ability to forage.