Have you ever seen one of these? This is a honey bee swarm - a bunch of worker bees with their queen. Swarming is a reproductive strategy of honey bees that occurs every year around this time. The colony is growing and running out of room. They start raising a new queen so that the old queen and a bunch of worker bees can leave to find a new home. It's this groups of bees that are called a swarm.
They will hang out somewhere suitable while scout bees seek out a new home. When they find a place they like, the entire mass of bees will leave for their new home. It might take a couple of hours, or a couple of days, but eventually they leave.
Give us a call or email (info<at>thebeeshed.com) if you have one of these beauties in your yard. We'll do our best to give them a new home!