When we were at Coimbra in the old library we were told that if they find insects are invading the books, they have bats come in and clean them. There are caves four stories below the library where the bats live and they have an access to the upper floors. The guardians have to cover everything at night so it doesn't get messy but when a book needs cleaning they bring it down off the shelf and place it on a stand. Apparently it's fan shaped and they fan the book over it so the bats can then get at the offending bugs on the inside pages. Talk about using the environment in olden days.
I thought that was very cool.