Swarms are a normal occurrence where the colony (family of bees) grows too big for their home (the hive). The colony will make a new queen and when born, the old queen will leave the hive with half the colony. They will settle on a branch while scout bee look for a new home.
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When a colony(the family of honey bees) grows too big for its home (the hive), the workers will “make” a new queen. When the new queen emerges, the old queen will leave the hive with approximately half the worker bees to find a new home. When they leave, the queen settles on a branch, a car bumper or whatever is convenient. The worker bees will then cover her while “scout” bees look for a new home. Once a new home is located the scout bees will return to the swarm and let the rest of the colony know through a scent and "bee-dance" the location of their new home.