Nock is their an already established hive using the front of this hive set up in the provided entrance area? If so are you sure there is not a knot hole or access somewhere in this area pictured? Other wise I, for one, have not seen a swarm land on an already established hive. But consider there are some here with much more experience than me which might have seen a swarm in this manner. If so maybe they will speak up. If you are sure it is a swarm what did you do? Or what are your plans?