Bumblebee life cycle: males and queens are produced

This page, and the pages linked from it show the yearly lifecycle of a bumblebee colony. You can either follow the lifecycle in chronological order by looking at all of the pages in turn, or you can skip to whatever part you are interested in by clicking the links on the left.

The 4 stages in the life cycle of a bumblebee colony

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. These eggs become either workers or queens.
  • unfertilised eggs which contain chromosomes from the queen alone. These eggs become males.

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 decides whether or not to fertilise it with sperm. The fertilised eggs develop into workers (females), and the unfertilised eggs develop into males.

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. The pheromone instructing workers to raise the fertilized eggs as worker bumblebees is switched off once the queen starts to lay unfertilized (male) eggs, so that any fertilized eggs laid after this are raised as queens. Also once the pheromone is switched off the queen loses some of her dominance over the workers, and this leads some of them to lay unfertilized eggs of their own (see below).

Bumblebee workers can lay unfertilised eggs

male bumblebee spending the night under a teasel flower

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 (eating their own sisters). 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. The queen will also attempt to eat worker -laid eggs (her own grandsons) and head butts and bites her daughters to try to maintain her dominance.

A recent study on Bombus terrestris showed that 10% of adult male bumblebees came from worker-laid eggs.

The photograph on the right shows a Bombus hortorum male who has spent the night inside a flower, and the one above right shows a male resting under a flower head.

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.

Have a look at his rear leg - it has no pollen basket. Only males and cuckoo bumblebees have no pollen basket.

Bombus hortorum male

Bombus lucorum male

The queen maintains dominance

The queen maintains dominance over her daughters by head butting and pulling the legs of the most aggressive workers, and it is believed that a pheromone which suppresses activity in the glands of the workers which would stimulate their ovaries to grow is also involved in maintaining the dominance of the queen.

Caste (queen or worker) determination in Bombus terrestris

The queen secretes a pheromone, which, if present within the first 5 days of larval life determines that the larva will develop into a worker. If the pheromone in absent, and if the larva receives sufficient food (more than a larva destined to be a worker) during her final instar she will develop into a queen. Consequently a queen larva is larger than a worker larva. It is believed that caste determination works in a similar way for other bumblebee species too.

New queens are just normal worker (female) larvae that develop into queens.

On the left is a Bombus lucorum male. In many species the male has a similar colour pattern to the workers, but has a greater abundance of yellow hairs.

Next, mating and colony disintegration>
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