Swarm season is upon us!
Swarming is the way that bees reproduce new colonies. It is a form of asexual reproduction.
When a colony swarms, it takes with it the mother queen and many of the workers.
It leaves behind young workers and brood and food and the comb. And most importantly, it leaves behind a "queen cell" which is a developing queen.
The colony that leaves will look for a new home and the colony that stays behind will attempt to get the new queen mated and she will then be the mother of the original location.
When a colony swarms, before it finds a new, permanent
home, it will stop on a branch or a post or a sign or any of a number of locations. At this point, the colony will send out a search party looking for a suitable new home.
When you see one of these swarms, leave it alone. Take a few photos and call a beekeeper.