From Dark and Darker Wiki
To add to that, I just played a game in the Crypts with good old death swarm and didn't see a circle or enclosing red area of any kind. As soon as I started taking damage from the swarm I started frantically running around the dungeon looking for somewhere I wouldn't take damage. But once again no visual indicator on the map aside from the timer, no circle and no red area. Is this a bug? (No pun intended lol)