I went into the winter with 2 hives that were thriving to all appearances. I've seen activity in both hives on warm days and have popped the top a couple of times to see bees on the sugar cake under the top, and heard noise when rapping on the side of the deep. I notice recently activity greatly reduced and then nil in one of the hives. I did an inspection today as it was warm and sunny and the hive is completely empty. There are perhaps 2 dozen dead bees on the screened bottom board, and a 10 or so dead bees that were in the act of emerging from brood cells. That's it. Zero other bees. Out of 12 full frames of honey there are about 6-8 full frames of honey untouched, a sugar cake about 25% eaten, a pollen patty put in in January untouched. Did they swarm on one of the unusually warm days in January/Feb? Why swarm and leave honey? The other hive has a ton of activity today. The only different between the hives was one has a screen bottom and the other a partially screened bottom. Other than that I treated both of them same and both were packed with bees in October. Treated both with apivar in July and December. What happened?