I did have that thought this spring when I saw the stains. I made a note not to split from them, not that they every gave the opportunity.
The way to check in a colony like this is to look at previously used brood cells and see how many of them have mite droppings. If you hold the comb so the sun is coming over your shoulder and the comb is tilted so you can see the upper sides of the cells, that will tell you the most. I have only seen that type problem with bees that had serious tracheal mite problems. The key is the splitting of the cluster. When bees avoid each other in the hive, it is always for a reason.
There is sugar all over everything, it's kind of hard to see mite feces, but I'll look when I get a chance.
Huh? Where did the sugar come from?
Fed it then tore the hive apart before they ate it. It's in the pictures though it's worse since I put the frames back in.