Went out to check both my yards today as we've had a bit of exceptionally nice weather and discovered I have lost 23 out of 30 hives. The bees were all dead in their cluster and they were over/near patches of brood which basically didn't hatch and those that did didn't emerge, just little holes in the cap, some had their tongues out of the hole. I brushed the clusters off with a goose feather and checked the comb under them in the sun and saw mite feces. All hives still had approximately 65 to 100 pounds of honey on them and plenty of pollen. Last year was the best year I've ever had as far as honey harvest and booming strong hives all season even going into winter. It was the first year I haven't done a mite count in the fall also. I usually don't treat and when I have treated it's with OAV only. I've never noticed any diseases other than mites in my apiary and if the bees were suffering from something I would treat to rectify the situation, but I've been lucky. The end of my 5th season is my worst season. One thing that was interesting was the size of every dead cluster was approximately the same size, about the size of a nice grapefruit. I'll be treating them in the fall with an OAV regiment from now on. I just closed up the entrances of the dead hives after cleaning them out so I could store the honey in the field until early - mid March.