Swarm in a tree but where did it come from?

Yesterday I was called to my out-apiary because of a swarm. It had settled in a tree right in front of the building where my elevated hives are kept. The swarm was about 10m up the tree; the hives are at a height of about 20m. There was no way to reach the swarm.

I had a spare hive ready for this. I put it out immediately, ensuring that there was a bit of used comb inside to give it a more hive-like smell. All afternoon the swarm stayed on the tree. After nearly 6 hours I had to go home. This morning I'll find out whether they have moved on. Hopefully their scouts have found and liked the new hive.

Immediately after setting out the new hive I tried to see which of my hives the swarm had emerged from. I couldn't tell. The entrance traffic still seemed busy in each hive. I expect to see a large amount of capping wax on the removable floor after a swarm, dropped as they fill up on honey, but it seemed a normal amount.

I was cautious about opening the other hives. I supposed that alarm smells from neighbouring hives might put scouts off (although I've no evidence that it will). I had a look into Hive C but it seemed normal. I looked into Hive D and found that moving the excluder has trapped drones in the super box, and that the Queen appears to be in the lower box. I noted a Queen cell in the upper box, above the excluder. Hive F is still dropping Varroa, but I imagine that quite a few of the phoretic mites have infected the newly laid brood. More on that later.