When do bees swarm?

Bees swarm in late spring in search of a new home. During the winter the queen bee begins to lay her eggs and the colony sets about rearing its young. As the weather becomes warmer and early flowers appear, the raising of young bees increases rapidly. By the end of spring the colony has become so overcrowded that a large number of the bees,including the old queen, leave the hive and establish a new colony.(questions & answers)