You can believe him, it CAN happen. (After all, with bees, anything can happen.)
Last Wednesday I was called to hive a swarm. It was a nice prime swarm and settled easily into the hive I brought it. I didn't see the queen but their behavior told me she was there.
Before I left, the fellow who had called me showed me another swarm in the area---a small one, about the size of a grapefruit. It was nicely clustered and hung on one branch that was easily accessible. I didn't have any more hiving equipment with me and they really didn't deserve that I find and dedicate another hive to them.
I decided to try something I had never done before: to merge two swarms. I cut them off their branch and simply placed the "grapefruit" into the hive with the prime swarm while the hive was still open. To my total surprise, they simply merged into one family without the slightest indication of resistance or agitation from either swarm. Not even the buzz of surprise that often greets you when a hive is first opened. I closed the hive and moved it to the position where I wanted to keep it. Still, no excitement whatsoever.
I'm certain that both swarms had queens---the prime, most likely a mated queen and the "grapefruit" almost certainly a virgin. I assume that eventually the two queens will meet and the virgin will eliminate the older queen. Another few days and I'll open it up to see just where things stand.
Yes, swarms can merge.
