> While that would work (randomly spawning and removing) I would like to have a consistent and persistent fauna.

Well, there are other options - easiest would be to make them spawn close. We could also just allow them to "bury" themselves into earth, then "unbury" themselves at a randomly chosen close location.

> They get stuck. Nothing is less interesting than an enemy that you defeat by exploiting pathfinding or making it get stuck somewhere.

I beg to differ. An enemy that you can defeat by getting it stuck easily is strictly more interesting than an enemy that you can't get stuck at all. Not saying that this might not be a good course of action, just arguing the logic.

> Because those animals will not be the main thing the player should want to care about.

Not sure what to make of that. Animals should have the same role as, say, a granite wall at the same place: Normally just left alone, but for certain tasks a problem that needs to be solved. The more of these selective disturbances we have, the more interesting it becomes to play. Build an elevator through that granite or have your Clonk walk through the nest of spiders every time? Or try to clean up that nest? Trying to make that a non-brainer one way or the other isn't really helping anyone.