swarming for a new queen

Today I learnt that bees "swarm" when the colony has reached capacity and a new queen bee is born. Half the colony remains in the existing hive with the new queen, and half the colony goes with the old queen in search of a new place to set up shop. As a bee-keeping novice, I kept my distance while taking a photo, but in full zoom. 

The Northey St bee keepers were getting ready to put this half of the colony in a new hive box.