Portuguese libraries have long relied on biological controls. The eighteenth-century libraries of Coimbra and Mafra host colonies of tiny bats. In summer the bats roost outside; in winter they roost behind the bookcases. Each night they earn their keep by feeding on bookworms and other bibliopests. Each morning the librarians earn their keep by sweeping up droppings. The micro bats might be helpful in Portugal, but larger bats, along with pigeons and damp, did much damage to the manuscripts at Durham Cathedral when it fell into neglect during the sixteenth and seventeenth centuries.
