 "Bats hang inside a cave in Cerro Azul, a large area protected for its archaeological importance, in San Jose de Guaviare, Colombia, September 23, 2024. Representational Image/Reuters")
A research team from the University of Georgia has discovered that several species of North American bats emit a distinct green glow when exposed to ultraviolet (UV) light.
The phenomenon, known as fluorescence, had been documented in a variety of other mammals in recent years, but never before in bat species native to this region.
The study, led by researchers from the University of Georgia’s Warnell School of Forestry and Natural Resources, examined preserved specimens from the Georgia Museum of Natural History in Athens.
When placed under ultraviolet lighting, the bats’ wings, hind limbs, and the thin skin between their legs — called the uropatagium — produced a vivid green luminescence. The results mark the first recorded instance of UV fluorescence in these bat species.
The researchers tested 60 specimens representing six different bat species: the big brown bat (Eptesicus fuscus), eastern red bat (Lasiurus borealis), Seminole bat (Lasiurus seminolus), southeastern myotis (Myotis austroriparius), gray bat (Myotis grisescens), and Brazilian free-tailed bat (Tadarida brasiliensis).
Each specimen displayed similar fluorescent characteristics, glowing within a wavelength range of 520 to 552 nanometres, a spectrum that gives the bats their distinct green appearance.
“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, professor of wildlife ecology and management at the University of Georgia and one of the study’s coauthors.
“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?”
How the discovery took shape
The research was initiated by Briana Roberson, then an undergraduate at the University of Georgia, who was inspired by earlier scientific papers describing ultraviolet fluorescence in mammals, reported CNN.
Her curiosity was sparked by studies such as a 2019 report identifying flying squirrels that glow pink under UV light — an unexpected revelation that prompted researchers around the world to start investigating the phenomenon across species.
“That (discovery) sort of set the world on fire,” Castleberry recalled. “Everybody then was walking around with the UV light, seeing what glowed the next time they shone light on it.”
Roberson’s study built upon this growing field, focusing specifically on North American bats. She systematically examined ten specimens from each of the six species, shining ultraviolet light on them in controlled conditions.
Each bat exhibited the same striking green glow, particularly from the wings and hind limbs.
The findings, published in Ecology and Evolution, are significant not just because they reveal a new biological property in bats, but because they deepen an ongoing scientific enigma: fluorescence has been recorded in over a hundred mammalian species, yet its function remains unknown.
What scientists tested — and what they ruled out
One of the main goals of the University of Georgia team was to determine whether this green luminescence plays any functional or ecological role.
The researchers began by exploring whether the glow might serve as camouflage, especially for species that roost in foliage during summer.
To test this idea, they compared the emission wavelength of the bats’ glow with the wavelength of chlorophyll, the pigment responsible for the green colour of leaves. The comparison revealed that the two did not match, making camouflage an unlikely explanation.
Another hypothesis considered whether the fluorescence could help bats distinguish between sexes or individuals of their own species.
However, every specimen — male and female alike — showed identical fluorescence patterns and intensity, ruling out sexual differentiation as a factor.
In addition, some species included in the study roost in open structures such as buildings or caves, environments where a bright green glow would not serve any protective purpose. This made the idea of environmental blending even less likely.
The researchers noted that the glow occurred in consistent locations across all species — on wings, lower limbs, and the tail membrane — areas visible during flight. While this could imply a behavioural or communicative role, such a function has not been observed or verified in live bats.
“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.
“It’s possible for glowing functions to be more diverse than we previously thought.”
Theories point to evolution — and unanswered questions
If fluorescence in bats offers no clear modern advantage, it might be a biological remnant inherited from a distant ancestor. Castleberry suggested that the characteristic could be an evolutionary holdover rather than a functional adaptation.
“The data suggests that all these species of bats got it from a common ancestor. They didn’t come about this independently,” he said.
“It may be an artefact now, since maybe glowing served a function somewhere in the evolutionary past, and it doesn’t anymore.”
The notion that fluorescence could be an ancient trait is supported by broader research into mammalian biology.
A 2023 study conducted in Australia documented 125 mammal species exhibiting some form of fluorescence under ultraviolet light. Lead author Kenny Travouillon, curator of terrestrial zoology at the Western Australian Museum, said that the discovery of fluorescent bats reinforces this growing trend.
“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 noted.
“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.”
Travouillon pointed out that fluorescence has now been observed in nearly 200 mammal species, ranging from platypuses and pocket gophers to squirrels and bats. With over 6,000 mammal species worldwide, scientists believe that many more examples are yet to be documented.
A puzzle far from solved
While the wavelengths observed fall within the visual spectrum that bats are capable of perceiving, it remains uncertain whether there is enough ultraviolet light in their natural nocturnal environments to trigger visible fluorescence during their active hours.
This limitation makes it difficult for scientists to confirm whether the glow has any direct behavioural or ecological importance.
“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.”
Roberson and Castleberry’s team pointed out that while the study does not yet explain why the glow occurs, it provides a crucial foundation for future research.
The next step involves observing live bats under ultraviolet light in controlled or natural settings to determine whether the fluorescence plays a role in communication, navigation, or predator avoidance.
Their findings also help highlight how much remains unknown about even familiar species. Bats are already among the most distinctive mammals: they are the only mammals capable of sustained flight, play critical roles as pollinators and insect controllers, and have highly specialised sensory systems.
“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?” Castleberry said.
“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.”
The growing field of fluorescent mammals
Since the first reports of glowing flying squirrels in 2019, research on mammalian fluorescence has expanded rapidly.
Scientists have documented various colours of glow—from pink and blue to green and yellow — across continents and taxonomic families. Each discovery raises new questions about the mechanisms behind the fluorescence and its biological meaning, if any.
In many cases, the luminescence originates from fur or skin proteins that absorb ultraviolet light and re-emit it at visible wavelengths.
Yet, the biochemical basis for these processes varies widely between species, making it challenging to identify a single evolutionary cause.
For bats, the presence of fluorescence across multiple unrelated species indicates that the trait may be deeply rooted in their lineage.
However, until living specimens can be studied in motion under ultraviolet conditions, scientists can only describe what they see — not why it exists.
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With inputs from agencies