Biologists find six bat species emit an eerie green light under UV, but the cause remains unknown

Your Halloween decorations might be more realistic than you think.
A new study by scientists at the University of Georgia has revealed that several species of North American bats give off an otherworldly green glow under ultraviolet (UV) light — and researchers are at a loss to explain why.

The finding, published in the journal Ecology & Evolution, shows that this ghostly luminescence appears in every specimen examined, across multiple species, sexes, and ages.

Researchers tested 60 museum samples from six bat species — the big brown bat (Eptesicus fuscus), eastern red bat (Lasiurus borealis), Seminole bat (Lasiurus seminolus), southeastern myotis (Myotis austroriparius), grey bat (Myotis grisescens), and Brazilian free-tailed bat (Tadarida brasiliensis).

Every one of them glowed a consistent shade of green when exposed to UV radiation, specifically on their wings, hind legs, and the membrane between their legs — and always within the same narrow wavelength range.

That uniformity, scientists say, rules out many of the most obvious explanations.
If the glow were meant to help bats identify their own species, attract mates, or deter rivals, researchers would expect variation in colour or pattern between sexes or species. Instead, all the bats glow the same — suggesting the phenomenon may have evolutionary roots rather than a current biological purpose.

“The data suggests that all these species of bats got it from a common ancestor,” said Steven Castleberry, a wildlife biologist at the University of Georgia and co-author of the study. “It may be an artefact now — something that served a function somewhere in the evolutionary past, but doesn’t anymore.”

The discovery adds bats to a growing list of unexpectedly fluorescent mammals. In recent years, scientists have documented glowing platypuses, flying squirrels, wombats, and even hedgehogs, each emitting distinctive hues under UV light.

Still, the bats’ consistent colouration remains puzzling. Their photoluminescence — the emission of visible light after absorbing ultraviolet radiation — might not even be visible to them in their dark, nocturnal environments. While the wavelengths fall within a range that bats can technically perceive, researchers doubt that enough ambient UV light exists in caves or night skies to make the glow noticeable.

However, the glow’s location on the animals’ bodies could be an important clue. The glowing membranes on their wings and legs are visible when bats are flying or foraging, suggesting that the phenomenon might once have had a behavioural or ecological role — perhaps aiding in communication, navigation, or predator deterrence.

The next step, Castleberry said, is to study live bats to determine whether the glow can be seen in natural conditions and whether it triggers any behavioural responses.

“We don’t yet know if this is visible to the bats themselves or if it’s just a quirk left over from evolution,” he said. “But we do know it’s widespread — and that makes it even more intriguing.”

Until those studies are done, the mystery remains unsolved. What’s clear is that America’s nocturnal flyers are carrying a secret light show in their wings — one that has gone unnoticed for millions of years.

So this Halloween, those glowing bat decorations might not be so far-fetched after all.