Thommy H:
Being in the army list they are by definition the only thing we know must live in the Dark Lands. Everything else is a guess, based on meagre background and some vague knowledge of ecology. And, more to the point, no one had suggested them yet, which struck me as odd because they’re the only thing we can say lives there with almost 100% certainty.
So, in fact, it is a suggestion with a bit more backing than anything else, which was what I meant.