What is Swarming
Swarming is a natural division of the hives population. When the number of workers exceeds the capacity of the hive, the workers will raise a second queen and she will travel to a new location with half of the colonies worker bees and Drones. Generally this occurs in the spring or summer months - 4 to 5 weeks after the queen begins laying eggs after winter. Each hive can swarm several times a year, often until August.
A new location is picked by scout bees who are workers that are skilled in covert operations. Scout bees will search out the best place to successfully relocate the swarming colony. This is often an existing bee hive in a tree, house or other established location. Important things to the scouts include drafts, accessibility, guard ability, size and location. Often though, a new suitable location is not found before swarming is necessary and the swarm will find unusual places to temporarily stay. This can be on the bumper of a car, around a mailbox, in the lower branches of a tree or as shown in this photo, on the corner of a picnic table. Often, you will find swarms within arm's reach.