Saw a black bee trying to get into my remaining hive yesterday, so today I checked in the morning and afternoon -- plenty of hives around to provide robbers.
Sure enough, this evening there was a big commotion on the landing board and bees fighting. I put an entrance reducer on, but it didn't really fit well, I'll have to go out tomorrow and pry up the bottom box, the slot is a bit tight. Or look for one I made that fits. Anyway, since it didn't go all the way in, I put some scrap wood on top and in front so that there is only a couple bee's width of space for entry and exit.
Things quieted down quite a bit. Stuffed a couple cracks between boxes as well (will glue some wood on this winter to close those up). I'll check in the morning to make sure they are still OK.
No bees got in the hive, none were leaving heavy and there are no traces of wax or honey on the entrance. I closed the upper entrance, and had a lot of bees investigating the seams between boxes, so I think I'm still OK. This hive isn't up to proper strength yet from superceding the queen a while back, another round of brood will get them up to scratch, but that's a couple weeks away.
Too late tonight, but tomorrow I'll probably make a robber screen and fix things up properly, I'd hate to lose this hive, they made a good honey crop too.