The University of Michigan shut down its library after venomous spiders were found in the building's basement.
University officials discovered a trio of Mediterranean recluse spiders in the building, as well as "remote areas" on other parts of the campus, located in Ann Arbor, Michigan.
Shapiro Library was shut down on Sunday and Monday so the university could address the spiders found.
"As the name implies, they are reclusive and bites are extremely rare," associate professor Anne Danielson-Francois said in a statement. She was one official who helped identify the spiders.
"Mediterranean recluse spiders prefer basement spaces, tunnels and other hideaways where there is a decrease in foot traffic," she added. "Users browsing the library stacks would be very unlikely to encounter a stray spider or be bitten."
University officials have since called the temporary library closure a "mistake" after students and faculty were unable to use the building for two days.
"A misunderstanding of the situation led the library to close for two days," university spokeswoman Kim Broekhuizen said. "Based on what we know now, library managers agree that it was a mistake to close the building and they apologise for the inconvenience to the university community."
Despite the "misunderstanding", the library was still treated for spiders on Monday out of an abundance of caution, the university said.
Students and faculty have since been allowed back in the building.
Those working in the basement of the library have been advised to wear long-sleeved shirts, hats, gloves, and shoes that enclose the entire foot as a safety precaution.