Flies actually do spawn already as corpses lie on the ground for a long while (10 rounds? I don’t remember exactly), buzzing around and crawling all over them. That is, unless it’s raining.
I experimented with wind moving through trees around the same time I added the flies but it didn’t look very convincing. Maybe I’ll look into it again at some point.
Breath effects in the cold is a pretty cool idea, definitely going to try that. As we add more terrain types, we’ll also add some more fitting weather effects, like dust storms in the wastelands, snowing in the north, and such.