We get a lot of calls about bees living behind the walls in someones house. The people who live here called another beekeeper a few years ago to remove a colony. After he/she removed them they (or whoever did the repairs) filled the cavity with these plastic balls. That is what needs to be done because another swarm of bees will smell that old colony and be attracted to that same location. When you fill the cavity, it needs to be completely filled. As you can see this cavity was not.