Adds a new biter faction: Toxic biters, spitters and worms! They spread a deadly poison cloud and may infect buildings, taking control of turrets and other things.
Once you've got the game open, go to Mod Settings. On the "Map" tab, there's an entry for this mod about "Big creature on clouds," which I suspect is about the boss biters but IDK for sure. If it is, I'd figure unchecking it will take care of the issue on a going-forward basis (but IDK what to do about any bosses that have already spawned).
ETA: do we know if that is actually what's making for bosses?