Rotwyrm

An erring Magister may call forth the Rotwyrms from any rotting or decaying matter that lies near him. Unthinking and unstoppable, these giant daemonic maggots wriggle towards their victim with terrifying speed. Not subject to physical laws, they can pass through any substance in search of their goal: the flesh of the Spellcaster. The stench of decay and the buzzing of flies indicate their presence.

Also Known As: Flesheaters, Wizard Worms

Attracted by: Green magic, Purple magic, spells of the flesh

Source

 * Warhammer Fantasy RPG 2nd ED -- Realms of Sorcery pg. 80