Sometimes turrets does not shoot these bugs even when they're clearly on the ground and crushing them
I guess there's some bug that won't change status from "flying" to "grounded" or smth
Or there's some wierd interaction with Krastorio (it's the only other mod i have now)

Also, I don't think I saw this happend to flyers below big ones (small and medium, i guess, work fine or it's just didn't happend back then)

Ah, yeah, tested in editor. Big and Behemoth ones never became targettable by turrets

Tested w/o any other mods
There are 3 types of the each tier of flyers and every tier had one flyer that never became targettable
So I guess, some of the untargettable ones (which, I think, are always in airborne status) can spawn naturally

Thanks for testing it so thoroughly, that helped a lot! Found it: flyers placed by a player (like from the map editor) were never handled by the mod, so the airborne ones never landed and no turret could hit them. That's why exactly one of the three versions of each tier stayed untargetable in your test. Fixed in 0.0.9, including flyers already stuck that way in a save.

I couldn't reproduce it in a normal game though (all tiers landed fine to attack turrets, even walled ones). If you see a flyer in a regular game that stays untargetable, please send me the save and I'll look into it.

Two hours in and no signs of untargettable ones
Thanks!

Also, while I was trying to fight those, got the idea. What if there was a synergy with new turrets - when flak cannons shoots flyers they have a chance to break their wings so they will stay on ground till death or full regeneration. I think, that might be an immersive feature
Anyway. cool mod, keep it up!