Six species of North American bats glow green under ultraviolet light, according to a University of Georgia study. The pink glow often attributed to bats actually belongs to flying squirrels.
Under ultraviolet light, bats glow. And no, that is not a Halloween gimmick. A study published in the journal Ecology and Evolution confirmed that six species of North American bats emit a green photoluminescence when exposed to UV rays — the first record of the trait in bats native to the region.
What the study found
Researchers at the University of Georgia's Warnell School of Forestry and Natural Resources examined 60 museum specimens from the Georgia Museum of Natural History, ten each of six species: big brown bats, eastern red bats, Seminole bats, southeastern myotis, gray bats and Brazilian free-tailed bats. Every specimen fluoresced.
The glow appeared on the bats' wings and hind limbs. Using a light-measurement tool, the team determined the emission peaked in the 520- to 552-nanometer range — a shade of green. The color and its location were consistent across species and between sexes.
A correction worth making: bats glow green, not pink
The claim that bats glow pink under black light circulates online, but it conflates two different animals. The famous pink biofluorescence under UV light belongs to North American flying squirrels, a finding first detailed in a 2019 paper. Flying squirrels — which are rodents, not bats — glow a vivid bubblegum pink. The bat species documented by the Georgia team glow green.
So while both stories come from the same small but growing body of research into fluorescent mammals, the pink glow is the squirrel's signature, and the green glow is the bats'.
Why do they glow? Nobody knows yet
The discovery raises a question the researchers cannot yet answer. Photoluminescence — the absorption of light at one wavelength and re-emission at another — has now been documented in roughly 200 mammal species, but its function remains unexplained.
"It may not seem like this has a whole lot of consequence, but we're trying to understand why these animals glow," said Steven Castleberry, the study's corresponding author and a professor of wildlife ecology and management. "It's cool, but we don't know why it happens. What is the evolutionary or adaptive function? Does it actually serve a function for the bats?"
The team tested two leading hypotheses and ruled both out. First, camouflage: bats roosting in summer foliage might blend in via a green glow, but the bats' emission wavelength did not match that of chlorophyll. Second, mate or species recognition: every specimen glowed at essentially the same wavelength, leaving no room for a distinguishing signal.
Because many bats can see the emitted wavelengths, the researchers suspect the trait may be inherited and used for communication — or it may be an evolutionary leftover with no present function.
"The data suggests that all these species of bats got it from a common ancestor. They didn't come about this independently," Castleberry said. "It may be an artifact now, since maybe glowing served a function somewhere in the evolutionary past, and it doesn't anymore."
Part of a wider pattern
The finding adds to a fast-growing list. A 2023 study led by Kenny Travouillon of the Western Australian Museum recorded 125 mammal species that fluoresce under ultraviolet light; Travouillon, who was not involved in the Georgia research, told CNN that the feature has since been reported in about 200 mammal species. With more than 6,000 mammal species on the planet, more likely remain unidentified.
"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. "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."
The practical stakes may be more than curiosity. Bat populations worldwide face threats from habitat loss, disease and climate change. Understanding how bats perceive their surroundings — including wavelengths their own bodies emit — could inform conservation and management, the researchers argue.
How to see it
None of this is visible to the naked eye. The glow appears only when the animals are illuminated with an ultraviolet, or black, light — the same tool backyard naturalists have used since 2019 to hunt for glowing squirrels. For bats, the next step is determining whether living animals glow the same way museum specimens do, and whether that glow means anything to the bats themselves.