The evidence on the floor of Hive E pointed to an occupation. That is exactly what has happened. At some point in the last few days a swarm has occupied Hive E. Welcome to Colony 12.
The signs that this was not a robbery included detritus which looked too dark to be from capped honey. That was a sign. The most striking thing though was the Wax Moth larvae. An infestation of Wax Moth must have been under way because there were 3 or 4 larvae on both times I looked.
I don't know the origin of Colony 12. I haven't seen evidence that it has come from one of my hives. If it had then Colony 04 in Hive D would be most likely. I don't see evidence that has happened, although there was less dropped pollen than on the floor of Hive G.
Colony 12 seems to be a decent size. It has arranged itself vertically through the hive, which has a Commercial brood body and a super on it.
I took the lid off to check that they really were occupying but I didn't lift out any frames. Their temperament seems fine. They didn't attack, even though I didn't use smoke.
I put a feeder on the hive with some of last years honey in it. I was concerned afterwards that this may be improper haste -- the settling swarm probably won't have exhausted the honey in their stomachs so there may be a greater risk of bringing a disease like AFB. On balance I don't think that I've done anything silly. The swarm wouldn't have needed to build comb so I'd already missed that opportunity to empty their stomachs. There have been few sunny days lately and lots of rain. The last of the spring tree blossom has gone so feeding looks like a good way to encourage brood rearing. I'll inspect in mid-June to see whether there are any disease signs.