A couple of things that I would check on 1) all that mold tells me that there was too much moisture and not enough air flow.
Possible, but I suspect all that mould grew post-mortem. Three other hives of the same dimensions and configuration have no mould visible when the top is removed, though I haven't manipulated those combs to check more closely.
Was the bottom entrance covered in snow perhaps? where you using an inner cover?
Yes, at one point the entrance had been covered in snow. This particular colony was probably already deceased when the snow level reached the entrance, however. No, I don't use inner covers on any of my hives, including my Langs, preferring a chaff-filled upper box per the good reverend's original 1852 specification. However, the hives were low on stores going into fall, so I ensured that stores were available by leaving a feeder atop each one. The chaff-filled box was then placed above the feeder. The chaff in all hives, including the deceased, is still dry and unmoulded.
You said that your feeder had 2 1/2 inches in it. Was this sugar syrup? Leaving syrup on a hive over winter is always a bad idea. this could be the source of the excess moisture. That combined with bad ventilation could easily kill the bees.
I'm not convinced. The feeder both allows a place for "excess" moisture to escape into and a resource for the colony to replenish stores when they run out of what's in the combs. This is exactly what appears to have happened with my other hives. Likewise, any water condensation on hive walls and ceiling make a good water resource on warm winter days. (See Dennis Murrel's site for reference on winter water resources. Similar observation made by Kieth Malone, in Alaska, as well as others.)
Note: the feeder is a Bro-Adam type. Majority of liquid surface - and therefore evaporated moisture from the syrup - is sealed away from the colony by the nonpermeable surface of the feeder-entrance dome, effectively creating a separate "room" with just enough access for the bees to get at a supply of syrup. Syrup leaches underneath the entrance dome into the feeding area due to an uneven surface where the dome meeds the bottom of the feeder. Gravity effectively keeps the levels the same, regardless of where additional liquid volume is added to the total system.
on a side note if you were feeding your bees then there is a good chance that your comb honey is not honey at all
best of luck
Certainly possible, but it looks as though the feeder was never touched. No dead bees, no detectable change in fluid level from when it was placed, and - oddly - no mould in the syrup. And, the honey tastes like fireweed.
Still, I'm likely to feed the honey to other hives in the spring. What most concerns me is the black along the edges of three combs. I simply do not know if this is some sort of direct moisture damage or a form of mould (though it has been sent to a lab). If it's black mould, I certainly will not eat anything from this deceased colony, but mould spores are large enough - relative to a bee - to not concern me when considering feeding to other bees.
Keep your comments coming in, please. Some of them do make me go back and reexamine things.
I find the differences between observations from framed hive (mostly Lang) and natural-comb hive (Warre and TBH) beeks extremely interesting, though most of the natural-comb beeks haven't commented in this forum.