The weaker of my two colonies is being robbed. 24 hours since I first noticed and the colony is visibly reduced in number. Hornets of some kind tho I don’t recognize them. Entrance reduced to a couple of bees, feeder on (1 to 1), and fingers crossed. I will try the wet sheet trick as well.

I probably should reduce the entrance on the other, more robust colony.

Any other suggestions? Thanks  

There is a lot of good information at beesource. Thanks very much for the tip. What I read there led me to open the hive and see what was going on and what I found was not robbing, but rather workers casting out the drones. The bee numbers are much reduced from when I first inspected in June. I looked for the queen but I’m not good at spotting her yet so I put most of my effort in trying to find eggs. There were none. And no uncapped brood. Only a few mature bees chewing their way out of the brood cells. There were quite a lot of empty brood cells. Most of them in fact. There were also no queen cells. The top deep box is completely full of honey. the flow super is about 1/3 full of capped honey.

I believe this colony is queenless. Probably for about two weeks. So, I ordered a BeeWeaver queen that should arrive tomorrow. Regrettably, YouTube is my mentor. Fingers crossed.