• Queen emerges from hibernation and starts new colony by herself.
• Workers (females) are produced and start to forage; the colony develops and grows.
• Unfertilised eggs (males) are laid and worker larva develop into new queens.
• Males and new queens mate, the colony disintegrates, the old queen, workers and males die, and new queens hibernate.

Male (unfertilised) eggs are laid and worker larva develop into queens.
The bumblebee queen can lay two types of egg; fertilised eggs with chromosomes from the queen and a male she mated with the previous year, and unfertilised eggs which contain chromosomes from the queen alone. The sperm from the mating is stored in a small container called a spermatheca located in the queen's vagina. As the queen lays the egg she decided whether or not to fertilise it with sperm. The fertilised eggs develop into workers (females), and the unfertilised eggs develop into males.

The photograph abve left shows a Bombus hortorum male who has spent the night inside a flower. Males do not return to the nest once they have left it, so spend their nights either inside or hanging under flower heads. In the morning they are often very lethargic and may appear to be ill, but this is normal. They just need to get up heat by drinking nectar or being warmed by the sun or both.

It is thought that fertilized larvae develop into queens and not workers once the queen stops sectreting a certain pheromone. These larvae are fed more frequently and for longer than other larvae destined to be workers.

The queen lays unfertilised eggs only towards the end of the colony life. After she has laid male eggs she may lay fertilised eggs that will become queens, but she will not lay any more eggs that will develop into workers, so the laying of male eggs signals the start of the end of a colony.

At about the same time as the queen starts laying unfertilised eggs that will produce males, the ovaries of some workers, usually those performing household duties, may develop. It is possible for workers (without mating) to lay unfertilised eggs that will develop into males, however workers cannot produce queens or other workers. Some workers try to lay eggs of their own, and may even attempt to eat eggs laid by the queen. This leads to aggression between worker and worker, and worker and queen. In many cases the more persistent workers will succeed in laying some eggs that will reach maturity.