Library Bats

In 2013, UNESCO designated the University of Coimbra a World Heritage Site, citing its architecture, culture, tradition, and historical value. This institution lies within the city of the same name, the sixth largest in Portugal.

Founded in 1290 in Lisbon and moved to Coimbra in 1537, the university is one of the oldest continuously operated in the world. It’s easy to see how the architecture added to a UNESCO bid: the place is gorgeous.

Of particular note is the Biblioteca Joanina, known in English as the Joanine Library. Named for King John V of Portugal, who founded it in 1717, this library is considered time and time again as one of the most beautiful on the planet.

As you might expect from an old European library, Coimbra contains a slew of ancient texts.

In fact, its 200,000 volumes are all hundreds of years old; it’s a repository for historical texts, eschewing the addition of new tomes.

Libraries of the distant past faced a big problem: how could they maintain their books? These days, we can construct buildings and rooms with climate-controlling mechanisms and monitor the condition of materials with accuracy. In 1717, however, keeping humidity down without an air conditioner was a difficult conundrum. Paper is wonderful for storing information, but how long can it last before it degrades? With poor conditions, the medium can disappear rather quickly.

The architects of Biblioteca Joanina understood this issue, building it to withstand some of the pressures of the environment. It was envisioned as a “perfect vault,” replete with 83-inch (2.11 meter) walls. These thick enclosures helped keep the temperature and humidity inside the library at consistent levels.

For the period, the engineering worked remarkably well. The library hovers between 64 and 68 degrees Fahrenheit year-round, while the humidity bobs around 60%.

No matter how well the library was conceived and executed, however, could stop another predator of paper: papirófagos.

This term means “paper eaters” in Portuguese and refers to insects. Certain species can subsist only on paper and library glue. To a papirófago, a library must be the most sumptuous buffet one could ever imagine!

Today, we have modern methods of prevention and remediation for insect infestations. Centuries ago, however, the issue wasn’t so straightforward.

Whether by accident or by plan, Biblioteca Joanina developed a natural defense to the paper eaters.

Bats!

Behind the stacks in the library lives a tiny colony of pipistrelle bats.

The dozen or so cute chiropterans sleep during the day but prowl on book-munching insects by night. And they’ve been doing so for hundreds of years!

The librarians leave some windows open for the bats to reach water sources in the town, though, apparently, this breach in the vault has minimal impact on the temperature and humidity.

For a bastion of higher learning, not much is known about the bat colony. No one seems to know exactly how long they’ve been in residence, whether they arrived at the beginning of the building project or gained entry later. Librarians know they have been there at least since the 19th century because, though they provide utility, not everything is positive with the bats. Receipts show the library purchased leather coverings for their long tables during the 1800s because the bats would drop corrosive guano on them overnight! Each morning, the librarians ritually clean up the bat droppings.

Is this tradeoff worth the natural pest control?

Obviously, in the 21st century, other methods of safeguarding the books exist, but the library seemingly wants to continue to harbor the bats. The winged creatures bring a lot of notoriety to Biblioteca Joanina, with upwards of half a million visitors a year coming through the World Heritage Site. Most are there to see the bats, which sometimes annoys the librarians.

The rub lies in the public’s general inability to actually see the bats. The colony is tiny, they sleep during the day, and the library closes at night. A tourist might hope to catch a bat exiting a window, but they are stealthy in the darkness. Sometimes, the librarians claim, on rainy days, the bats chirp in the late afternoon, perhaps thinking nightfall has come early. That’s about as much a performance as a patron gets from the bats.

They save their real work for the papirófagos.

As bizarre as it is to have bats living symbiotically in a library for centuries, Portugal features another scholarly quirk: Biblioteca Joanina isn’t the only library in the country with an insect-ingesting bat colony!

Lisbon’s Library at the National Palace of Mafra has a colony of grey long-eared bats and a few serotine bats. They, too, feast on insects before prowling nearby gardens.

The Portuguese love their bookish bats!