This summer we found out that a swarm of bees had moved into a cavity in a dead tree on our place.

I had to be quick to get this closeup (below) before the bees began to let me know I was not welcome.

When the weather cooled they became a little less active and I could get even closer, briefly.

As winter came on, I wondered if the bees would wall off part of the opening, to keep warmer. I asked our local librarian, who is also a beekeeper, and she told me that this wasn’t typical bee behavior (although they may seal small cracks), and that they’d be fine in our climate. Somewhere further north, I assume they choose more protected locations.
Bees stay warm by clustering together and doing the bee equivalent of shivering to generate a little warmth. They live on stored honey during this time. Some individuals will die over the winter and their bodies will be hauled out of the hive in spring. But the majority, and the queen, will survive.
Now that we’ve had some snow, and 18°F days, I went to check on the bees. None were visible and I got closer and closer until my head was right at the opening. And I could hear this wonderful sound of the bees buzzing deep within their tree! I listened for a few minutes until the bees became aware of me and one flew up to send me on my way.
There are, according to Wikipedia, no honey bees native to North America, so this lot or their ancestors must have originated in a swarm of honey bees from a beekeeper’s hive. We are delighted to have them, and our librarian-beekeeper told me that many beekeepers are looking to honeybees who’ve survived on their own, for resistance to whatever is causing the colony collapse disorder that has wiped out so many bees in man-made hives. But “our” bees can just stay where they are as long as they like.