Britannica Sources used in this answer

Why do honeybee colonies swarm?

Created from Britannica articles using AI. AI can make mistakes, so verify using Britannica articles.

bees on a honeycomb — Beekeeping Bees on a honeycomb.

Honeybee colonies swarm as a natural method of propagation or colony increase. This behavior is primarily triggered when a colony becomes overcrowded with adult bees and lacks sufficient cells for the queen to continue laying eggs.12

When these conditions occur, worker bees select several larvae to develop into new queens, feeding them copious amounts of royal jelly and enlarging their cells. Shortly before these virgin queens emerge, the mother queen departs the hive accompanied by a large portion of the worker bees—typically numbering between 5,000 and 25,000.12

This mass of bees temporarily clusters on a structure, such as a tree branch, while scout bees search for a new homesite. Once a location is found, the swarm relocates to establish a new colony. In the original hive, the first virgin queen to emerge typically eliminates her rivals to become the new sole queen. Beekeepers can often prevent swarming by manipulating the hive to ensure the queen has adequate space to expand her egg-laying area.123