Wizard lice

Wizard lice were a species of magical louse, tiny parasitic insects found in the land of Zakhara.

Description
A wizard louse usually measured $1/16$ of an inch in length, making them very difficult to spot.

Ecology
Though generally harmless in small numbers, wizard lice bred rapidly, forming a nest on each host they infested. They fed off of memories and magical energy. They were particularly harmful when attached to wizards or priests, capable of erasing one spell per day from their host's memory.

A host infected with wizard lice needed to bathe with strong soaps or cleaning agents to effectively kill them. The cure disease spell was also a reliable method used to destroy wizard lice.