Certain species of bats can glow under UV light. Scientists don’t know why

Glowing bats may sound like Halloween decor, but researchers in Georgia have discovered certain species of North American bats that are capable of the unusual trick.

When placed under ultraviolet lighting, six species of the critters were found to emit a green luminescence. It is the first record of the phenomenon in bats native to that part of the world, according to an October 20 news release from the University of Georgia.

The discovery adds to the growing list of mammals that share the trait. But scientists still don’t know why some furry animals glow while others do not. The findings were published in July in the journal Ecology and Evolution.

“What was already really established before this project, was that a lot of mammals glow under UV light. So, then the question was: Why do they glow?” said study coauthor Steven Castleberry, a professor in wildlife ecology and management at the University of Georgia. “We’re trying to learn more about bats and how they function in their environments and how they contribute to the ecosystem. … If we can figure out the function, if there is a function, it can help us to better conserve and manage these species.”

Green glowing bats

The lead author, Briana Roberson, an undergraduate at the University of Georgia when the study was conducted, was inspired by literature that had detailed mammals exhibiting the glowing function. One of the first reports of this feature was a 2019 paper, which found that flying squirrels fluoresce under UV light.

“That (discovery) sort of set the world on fire,” Castleberry said. “Everybody then was walking around with the UV light, seeing what glowed the next time they shone light on it.”

A 2023 study published by scientists in Australia recorded 125 species of mammals that glow under ultraviolet rays. Research from other parts of the world also looked at certain bat species and their florescence, such as an August 2024 study that found the toes of the Mexican free-tailed bat to glow under UV.

Roberson decided to take up her own research on glowing mammals, focusing on six species of North American bats: big brown bats, eastern red bats, Seminole bats, southeastern myotis, gray bats and Brazilian free-tailed bats. She visited the Georgia Museum of Natural History in Athens and shined a UV light on 10 of each species, making for a total of 60 specimens. Each of the critter’s wings and hind limbs gave off a green photoluminescence, Roberson observed.

She and her team set out to determine the function of the fluorescence by analyzing the wavelength at peak luminescence. Their first hypothesis was that the bats, which roost in leaf foliage during the summer, use the glow for camouflage. But when the researchers compared the wavelength of the bat’s glow with the wavelength of chlorophyll, the green pigment involved in photosynthesis, they found that the colors did not match.

They then tested whether the bats use the glow to identify differences in fellow bats, such as determining their sex. However, every specimen ended up having the same wavelength.

The function of the glow remains a mystery, but the study authors said they hope the answer is revealed one day, helping them understand how the animals respond and adapt to environmental changes.

“Bats have very unique social ecology and sensory systems, and the characteristics we found in these species differs from many other observations in nocturnal mammals,” Roberson said in a statement. “It’s possible for glowing functions to be more diverse than we previously thought.”

But it’s also plausible that the fluorescence does not have any ecological function, Castleberry said, or that the trait had a function in the species’ evolutionary past but no longer does.

More fluorescent mammals to be found

Kenny Travouillon, a terrestrial zoology curator at Western Australian Museum, said that the findings of the new study further confirm that fluorescence is common in mammals. Travouillon was the lead author of the 2023 study and was not involved in the new research.

So far, the glowing feature has been reported in around 200 species of mammals, Travouillon said. With over 6,000 species of mammals on the planet, there are likely many more to identify with this trait, he added.

“Since fluorescence is found widely in mammals, it is most likely that this feature was inherited a long time ago by the ancestors to all modern mammals,” Travouillon said in an email. “Why do they glow? We don’t know. So continuing to do research on this topic is important, as we may eventually be able to know the answer, and this may lead to more questions.”

Taylor Nicioli is a freelance journalist based in New York.

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