Set up bait hives well before the swarm season begins. Have one bait hive where you can see it every day. It serves two purposes. First, physician if your bees or any other colonies, whether wild or belonging to your neighbor, are preparing to swarm, they’ll explore your bait hive. If you see activity around the entrance, check the area around your apiary for stray swarms. Swarms nearly always settle in line of sight from their colony entrance. You can catch a swarm that may or may not choose the bait hive.
Second, you may catch a swarm that would otherwise be lost from your apiary, or you may pick up a swarm from somewhere else. Remove it from the bait hive and put the bait hive back up. Pre-occupied bait hives are more attractive to other colonies and you may pick up a second and even a third swarm from the same bait hive in one season. A bait hive can be as simple as an old hive that has been retired from service. You can find more information on bait hives in the book Making and Using Bait Hives.