Swarms are collections of Honey Bees that have left their hive and are looking for a new location to start a colony. They are typically seen as a large mass of bees clinging to an object or structure. These bees are in in transit to a new home. They are not a threat and you should not kill or spray them. Hire a professional for a safe bee removal.
Bee infestations are extremely destructive for homes and other structures. If you have bees in your wall, you need them out ASAP. The bigger the colony becomes the harder and more expensive it becomes to remove. Whatever you decide, just don't spray them. Hire a professional for a safe bee removal.