Bats Preserve Books at Johannine Library

Bats are part of this Portugal library's cleaning crew.

WORDS Laura Beausire
November 2019
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The Johannine Library at the University of Coimbra. / Alamy

The bats of the medieval city of Coimbra, Portugal, seemed to have abandoned the Dark Ages for the Enlightenment. Though they once lived in caves, they now reside in rather opulent digs: the Johannine Library at the University of Coimbra. By day, three librarians and two conservators keep the 300-year-old library in shape, carefully monitoring the temperature and humidity. But once the sun drops, a colony of bats flit throughout the space, dining, in midair, on insects that might otherwise harm the books and rare furniture. “The bats are welcomed as honorary librarians for their part in preserving the books from the bibliophagous insects,” says António Maia do Amaral, deputy director of the general library of the University of Coimbra.

With three stories of gilded bookcases, embellished balconies and nearly 56,000 volumes printed between the 16th and 18th centuries, the Johannine is cited today as one of the most beautiful libraries in the world. Bookshelves are made of local oak, but the large tables and benches were crafted by Italian wood-carver Francesco Realdino from precious Brazilian woods such as pau santo, mahogany and ebony. All this historic preservation can be partly credited to two species of bats: the Tadarida teniotis, a long-tailed bat, and the Pipistrellus pygmaeus, a microbat found across Europe.

Though the library’s walls are more than six-feet thick, the winged mammals have figured out an exit strategy. “The small bats hunt inside and outside the building and use well-known paths through gaps in the main doors,” Maia do Amaral says. In fact, when the library’s impressive wooden portal was restored in 2015, those existing gaps were meticulously maintained, mostly for the bats. As for the furniture, human workers spread large leather sheets over the tables each night to protect them from bat droppings, and then remove them each morning.

The odds of spotting a bat during a library visit are rare since the nocturnal creatures are typically asleep upside-down during Johannine’s hours of operation. However, when the library hosts the occasional evening concert, the furry fliers have been known to swoop down for a visit. “They sometimes fly out of the back of the shelves where they spend the day,” says Maia do Amaral, “for the pleasure of the audience and the concern of the performers.”

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