Nyth should appear non-hostile until you get near them. That way people unfamiliar with nyth will be drawn to their lights and lured into a false sense of security.
Despite the small amount of people who lack Nyth experience, the sheer immersive, atmospheric quality of something like this would be awesome in itself.
I wouldn't mind applying this to a lot of things.
Like "glowfly" which when you get near them disappears and some huge hulking stealthed aberrant appears with a description of some dangling light hanging from a tentacle to lure stupid adventurers to their death.
I'd be all for this as well if something was added to give incentive for PCs to investigate these creatures rather than simply avoiding them when they see them. Something as simple as capturing "X" number of glowflies and delivering them to NPC X would work, giving PCs a reason to determine whether what they're seeing is an actual glowfly or some sort of aberrant angler fish.
This seems like a cool suggestion. There's already systems in place that periodically spawn ambushes, maybe their frequency could be increased and more varieties added?