Probably impossible.

Gnat spawning seems to be tied into the whole "wonderwood" planetType and that part's hardcoded into the executable.

The template `data/templates_12.xml` handles turning most of the wonderwood world paramters, but there's no obvious gnat control. There is a that I can't pin on anything so maybe that's what spawns random gnats?

Unfortunately the gnats-in-rooms are configured per-room. So you'd need to edit all the rooms and configure them with zero-gnats and distribute them with the mod.

Also I don't there's a way to "partial" remove behaviours, only add them. So I think if someone were to make a mod, it'd be more likely creating a new GnatlessWood world. :/

If it bugs you that much, the easiest way would be to use the Editor. In Tools menu there's a "Animation/Sound/Tech/Other Editor..." if you open that there'll be a window with a tab on the right labeled "Initial Equipment". Hit the "new" button and search for "ww_toad_bladder" and set the count to 999 and "ww_gnats_pump" and set the count to 100. And set "include planets" for both to "wonderwood" so you only have to deal with them on that map.

That way you'll start the game with probably more bladders you'll ever need and pumps you can scatter around everywhere.

So I removed this line of code from "data/templates_12.xml":
And this removed all random gnat spawns even after playing 2+ hours. :)

The gnats are still in the underground rooms, but this removes 90% of the annoyance for me. I'm not sure how to remove them without editing the 30+ rooms one by one. :/

Spent a few more hours digging into it testing via playing, and tried removing references to "gnat_rooms" from Levels/wonderwood.xml, but it just resulted in crashes. :(

As far as I can tell, just removing the PoisonZoneController behavior removes all the random spawns, but the only way to remove the gnat spawns from the underground rooms is to set the flag on each of the rooms, which... it not only painful to do manually, but will be painful to make a mod that integrates the wonderwood change. :/

Thanks so much ! Gonna give this a try now and play . They really ruined my game by spawning in my base