Librarians have long fought against three primary antagonists: people who talk too loudly, those who not return their books on time, and book-eating bugs. Stern words and fines can take care of the first two offenders, but when it comes to the third problem, the guardians of the world’s books need to look to other types of deterrents. Librarians at Portugal’s Biblioteca Joanina and the Mafra Palace Library, use special nighttime security guards to protect the priceless pages: bats. The bats, which are less than an inch long, roost during the day behind the libraries’ bookcases. Once the sun sets, the winged residents emerge and feast upon the insects that favor snacks made of the printed page.When workers arrive in the morning, they find the bats have returned to their places of slumber, leaving behind a thin layer of bat droppings over everything. Before visitors can enter the buildings, workers must clean the floors and remove the covering that is placed over the furniture each night.No one is sure just how long this method of pest control has been employed, but it appears to be quite effective. Both libraries have been in existence for nearly 300 years, and they show no sign of slowing down.