While I agree that it could be safe with our continued efforts, I feel as long as we haven't found the nymphs and removed the roach swarm, this settlement is not safe for non combatants. And if these ankheg nymphs are a brood, then their parents might not be too far off, though they could be. Insects are different from mammals that way. Poison seems useful but if you don't know what you're using, you can very well poison yourself with it.