Mystery hive death?

My hive didn’t winter over, but I just can’t figure out why.

Last fall I checked honey stores, checked for mites (no treatment needed based on counts), and made sure the everything was in good shape: insulated tented lid for moisture control, elevated off the ground, etc.

In December, I went out one day and was surprised to see a large pile of dead bees outside the front entrance. It was hard to tell exactly how many because of snow and vegetation, but it seemed like way too many. I didn’t open the hive, since I figured that with a decreased population and good honey stores, heat saving was my biggest worry.

I finally had a warm enough day today, so I went out and opened the hive, and I don’t understand it. It’s clean, dry, full of honey, no pests that I can see, but the remaining bees are all dead. They’re not clustered or fallen – it’s like Pompeii, they’re all dead in perfect lifelike positions, head or tail in a cell, walking around, etc. It smells sweet and dry, no rot or chemical smell.

What the hell happened? What killed them? Is the honey and wax usable, or should I assume that whatever killed them contaminated it?