Silverfish

Giant Silverfish (Creature 0), Silverfish Swarm (Creature -1)

In an interesting twist to the pest's life cycle, some spellcasters incorporate giant silverfish moltings into their spellbooks and scrolls. These shed skins have the consistency of onionskin and are valuable due to the superstition that they contain residual magic from texts the silverfish consumed. Regardless of whether a silverfish molt has any intrinsic magical power, many tenured mages feel that proof of a book-devouring vermin's demise is worthy of a reward. Thus, such a trophy is guaranteed to fetch a tidy sum from the right buyer.