During spring the number of occupants in the colony has doubled with a population around 40,000 to 50,000. The colony can be so over crowded the bees prepare to swarm. The workers start constructing queen cells by feeding selected larvae large quantities of royal jelly. A few days before the new queens hatch, the bees stop feeding the old queen royal jelly, this causes her to loose weight giving her the the ability to fly again. The last time she flew might have been on her mating flights. See swarming
Half of the bees (usually the older flying bees) and the original queen leave the hive in a rush and settle onto a nearby tree. Scouts bees spend time locating a new cavity and when consensus is reach the bees take flight and move into their new home. Back in the old hive, the first queen to hatch kills the unborn queens unless the bees prevent her from doing so. If prevented, another (secondary) swarm will leave the colony. These are smaller than the primary swarm and contain an unmated virgin queen.
When the new queen is mated she resume as head of the colony, her first job is to repopulate the colony with workers and a few drones. With the end of the swarming season, the bees settle down and forage to restock their honeycomb with honey and pollen.