Bees swarm when going out to start a new hive. A swarm may contain from 1,500 to 30,000 bees including, workers, drones, and a queen. Swarming is an instinctive part of the annual life cycle of a honey bee colony. It provides a mechanism for the colony to reproduce itself. Overcrowding and congestion in the nest are factors which predispose colonies to swarm. The presence of an old queen and a mild winter also contribute to the development of the swarming impulse. Swarming can be controlled by a skilled beekeeper; however, not all colonies live in hives and have a human caretaker.