After I wrote about Pseudoscorpions last week the question came up why they are also called book scorpions. The book scorpions were first noticed by Aristotle, who probably found them among scrolls in a library where they would have been feeding on booklice.
Similar to the book scorpion which is not a true scorpion, the booklice are not true lice, they are members of an order called Psocoptera. These Psocids are tiny insects that live in damp environments. They eat mold and mildew. They are called either barklice or booklice. The name barklice probably comes from the observation that outdoors they gather under the bark of trees. The name booklice comes from the fact that they gather on older books in damp homes where they feed on mold but also on the glue which holds old books together.
Book lice are only found in places where old books are stored. That's because newer books use synthetic glue, which book lice can't eat - they only like the starch-based glue of olden days. The latter is also more prone to start molding.