The library Biblioteca Joanina is part of the University of Coimbra. The university was started in 1190 AD by the Jesuits. The world renowned library was built in 1728 AD. It houses over 250,000 ancient books, mostly in Latin.
The paper in these old books is susceptible to insects. While it is a very controlled environment. At night the wildlife come out, bats patrol the insect population in the library. Each morning the bat guano is removed from the library.