Bumblebees are not solitary - they live in small colonies of at most a few hundred bees. In spring, the queen will emerge from hibernation and start to make small nests in a hole in a hollow wall or discarded mouse-hole or even a tussock of grass. She makes a few cup-shaped wax cells and lays an egg in each, and then gathers pollen and nectar to feed the grubs when they hatch. Eventually these will become ‘worker’ bumblebees, smaller than the queen, and will take over the job of gathering pollen and nectar. There are no male bees at this stage. Over the weeks, the little colony will grow and may eventually contain a few hundred workers, attending to comb that has a rather disorganised and random arrangement.
Towards the end of the season, as the nest starts to deteriorate, the queen will lay eggs, some of which will become male bumblebees and some that will become new queens. When they hatch, the new queens fly off and mate with males from other nests. Eventually the nest disintegrates and the old queen and the worker bees die. The young mated queens find somewhere cool to hibernate over the winter months, to emerge again in the spring and start the cycle over again.