Appear in: The Descent (2005), The Descent: Part 2 (2009)
Scariest moment: The first clear, in-your-face shot of the monsters comes through a character's video camera, set in Night Vision mode, that pans across the cave and reveals a crawler standing inches behind another character.
Weakness: Blindness, which prevents them from finding prey without hearing the targets' movements.

Neil Marshall didn't need to introduce monsters at the start of The Descent's third act. Throughout the film's first creature-free hour, the writer-director's claustrophobic, unbearably tense feature plays more like a thriller than horror, getting up close and personal with a group of female spelunkers finding themselves repeatedly trapped in narrow caves and crumbling, constrictive walls.

Just when you don't think The Descent can get any more suffocating, though, Marshall unleashes his army of blind, inhuman ghouls. Stalking the ladies through sound, not sight, the humanoid crawlers tear through flesh and snack on innards as a means of survival, not simply to express villainy. Nevertheless, their murderous, unrelenting actions are stained-underwear material.