Bumble bees are commonly seen in spring and summer time. All the fairly large bumblebees seen flying in early spring, are overwintered queens busy feeding and searching for nesting sites. Some bumble bees nest in cavities underground, whilst others nest on the ground in rough grass or moss. The nest comb and brood-cells are made from a waxy material produced by the bees from special wax glands on their bodies and the whole nest is covered and protected inside a ball of dead, finely shredded grass, moss, animal fur or similar materials.
The smaller bumblebees seen foraging on flowers through most of the summer are workers. The queen rears the first brood of workers herself, but then the worker bees take over this duty whilst the queen devotes herself to egg-laying.
Bumblebees feed on pollen and nectar and rear their grubs on the same diet. Towards the end of the summer bumblebee colonies produce males and new queens. The males do not work in the colony and quickly leave the nest to search for, and mate with, the new young queens from the colonies. Once fertilised the young queens also abandon the nest to start their winter hibernation. Male bees die after mating, and when young queens have departed, the rest of the colony soon perishes and dies.
Bumblebees can sting, but rarely do so except in their own defence and usually only if actually handled. Generally bumblebees are quite docile and non-aggressive and go about their business with little attention to human activity. If you disturb a nest when gardening simply leave and the bees will soon repair any damage.
There is no real justification for destroying bumblebee colonies. Mostly they go unnoticed, but a small inconvenience due to the position of a nest is more than repaid by the immense value of these insects as pollinators of many flowers and plants.