We stayed in a B and B in an historic house in Ste. Genevieve. At breakfast Thursday morning the owner noticed this in a blooming red bud tree in the yard. He told us that it was a bee swarm, something I'd never heard of. We learned something. This is part of the reproduction cycle of honey bees. It happens in the spring, when a single colony splits into two or more new colonies. I am quite bee-phobic so I got out the telephoto lens to take this. https://en.wikipedia.org/wiki/Swarming_(honey_bee)
This was just inside a fence by the sidewalk and the owner was concerned about neighbors who might be more curious than informed, The local bee person was summoned. He had a box scented with lavender, of all things, which attracts the insects, and used a smoke stick to nudge them off the tree into the target. When we returned in the late afternoon they were gone.
By the way, we liked the B and B and recommend it. https://www.hertichhouse.com/