I haven't seen my hives in two weeks so imagine the surprise when I checked them and on my way back to the house I see a swarm in a nearby tree! Normally you reverse your hive bodies to ensure the bees think they have plenty of space and they don't swarm. I guess I missed something.
Capturing the swarm is relatively easy, just climb a ladder and shake them into the box. Then dump the box of bees into a hive.
Photos to follow: