Bookworm (Hazard, Vermin)
A bookworm is a tiny, one-inch long gray, seemingly normal worm. This miniscule creature is the bane of sages, scholars and wizards, for its primary source of food is the leather, paper, and wood that that make up books.
Bookworms cannot harm living creatures, but they burrow through plant-based materials and leather very quickly. Ignoring the hardness of these materials, a bookworm swarm deals 3 points of damage per round to dead wood, leather, paper and rope. Quick and agile, bookworms have a speed of 20 feet and avoid being detected by their ability to change their body color (DC 20 Perception check). Not even magical leather armor and wooden weapons are immune to the effects of bookworms, merely taking longer to destroy.
Magical writings, such as scrolls and spellbooks, are a favorite target of bookworms. Scrolls are destroyed in a single round and any spells contained on it are destroyed as well. A spellbook loses one spell level per round that a bookworm swarm spends burrowing into it. For example, a standard spellbook has 100 pages and can hold a maximum of 100 total spell levels (a spell takes up one page per spell level, minimum one page). Thus, it takes the bookworm 100 rounds (10 minutes) to completely destroy a full spellbook. If the same spellbook only had 20 spell levels in it, the bookworm would destroy the spellbook in 20 rounds (2 minutes). Multiple bookworm swarms can destroy a spellbook much faster.
A typical lair (or brood) contains 10 to 40 bookworms. They are easily killed by attacks that deal damage over an area (such as cold or fire). Consider one worm killed for each point of damage dealt.