About 10 days ago a friend called me to retrieve a swarm in their back yard 6-7 miles from my bee yard. It was close to noon and I indicated it'd be about 4pm before I arrived which was OK. I arrived on schedule for one of my easiest swarm captures ever. They were hanging on the cross brace of a fence 3' off the ground,10 min and they were in the hive body. I left it sitting on a fence post until dark and then picked it up moving it to my bee yard. I was by there 3-4 days later looking inside with all appearing as it should. I went by today and noticed no activity discovering this swarm had up and left this hive. I had provided 4 drawn frames with the balance in new foundation.
I've caught 30 or so swarms over the last 20 years with this being a first for me. My question is; Why did this happen?