I find the greylings are always popping up with every other tree I chop down. Less often when I simply pick up branches or just a bit ago leveling a lot of ground. I was gardening and a greyling came by. I built a fort next to a Black Forest pocket (and by pocket, I mean I could fit my dock home in it and not much else.) I've had all greylings and a troll spawn in this thing. Even after cutting all the trees out of it, they all spawned in. Thankfully I walled it off for protection, but still, it's awkward seeing armies come from nothing.

My home typically stays dark, so that may be my spawning problem, although skeletons paid my forge a visit after being here for like 100+ days? Like, why? Not a problem, just puzzling.