I love catching swarms. It is easily my favorite part about keeping bees. Putting out traps to catch swarms from feral colonies is a great way to improve the survival rate of the bees. Most of the premium nesting cavities in a given area are already taken if there are feral bees in your area. The typical swarm struggles to find a good location to set up shop before they run out of resources. Giving them a nice box to settle in improves their chances a great deal.