April & May are when you are most likely to have a honey bee swarm show up on your home or tree or any place that can provide a little bit of shelter for them. When a a colony gets to be too large, a queen and many workers will fly off to find a new spot to set up a hive. Most of the time they are just passing through. If a hive is stopped for a day or more it may be a good idea to have a bee keeper out to take a look. Bee keepers can either relocate the hive or incorporate them into their colony. Otherwise they should move on, on their own shortly after they arrive.