Lost the bees

Last night I got home to find no activity in the hive, even when I gave the entrance a friendly little scratch. I went inside to relax, but worry about the hive was bothering  so I decided to pop the lid and take a peek. The hive was dead, it had to have happened within the last few days. The bees didn't starve, they still had plenty of honey. There was a strange crystalized residue in the cells throughout.  I knew their numbers were low, but something killed them all at once. Another strange thing, while cleaning out the hive (back breaking work) I found the queen cage that I installed last summer after the hive had cast off a swarm and gone broodless for weeks. The exit from the cage was sealed with propolis. I cut the cage open and surprise, surprise there was the queen with her attendants entombed. There was no problem with the way the cage was installed, and it's possible that the bees sealed her in after she died, but it was shocking to discover her with the little blue dot, her poor life cut short by an unwelcoming welcome committee.