Originally posted by Kinox:

I came across surtling nests in plains biome. Is this normal or is there bug in world generator?

For clarification, location is north and no way near ashlands that could have bled over. Just really odd sight.

I've run into one (but only one) like that over the course of 8 or so worlds. A single jet of fire in the middle of a plains nowhere near a swamp.