A floor trigger opens holes in the walls, and millions of army ants pour in from all sides! All characters in the area take 1d4 HP damage per minute from ant bites and stings. Attacking with conventional weapons is fruitless. Optional: Characters may have a chance to react before being covered in ants; retreating might be possible; fire or magic might work; if there's a large pool of water nearby, characters might be able to jump in; etc. Optional: No AC/Dex rolls/Saving Throws allowed (there's too many ants, and they can get between any chinks in character armor); only magical protections are factored in.