This is a swarm of bees that I caught last year. "Swarming is the process by which a new honey bee colony is formed when the queen bee leaves the colony with a large group of worker bees. In the prime swarm, about 60% of the bees leave the original hive location with the old queen. This swarm can contain thousands to tens of thousands of bees." While swarms are not typically aggressive, if they are not re-hived they may move in to your walls or another dark dry place. Please do not attempt to kill the swarm. Most beekeepers remove and re-hives swarms free of charge. If you are within an hours drive of Philadelphia contact me directly at 484-243-0473 or at Eli.stamour@gmail.com . If you live farther away contact a local beekeeper in your area.