Honeybees reproduce by swarming. As a spring hive expands due to abundant food availability, it is typical for it to outgrow the space it occupies as it produces more bees and wax comb. In response, new queens are reared in anticipation of a swarm event. Near the time of the emergence of a new queen, the old queen will leave with half the worker population in order to find a new home. This mass of bees is a swarm. The net effect is two colonies of honeybees from the original hive.
It is important to not panic if you see a swarm. Although a swarm may look intimidating, it is very docile as these bees have no honey or eggs to protect. If you see a swarm, call us in order to have it moved to our apiary. They just want a home to call their own.
A swarm collection from an Australian beekeeper. Look how easy it is! Only a few thousand bees at most!