Night skies conceal more than silent wings. A new study at the University of Georgia has found that certain North American bats radiate bright green hues when exposed to ultraviolet light. What appears to be a glow-in-the-dark trick may have more profound implications in bat evolution and communication.
How Did Scientists Make This Discovery?
Researchers from the Warnell School of Forestry and Natural Resources examined 60 preserved bat specimens belonging to six species, including big brown bats, eastern red bats and grey bats. When exposed to ultraviolet light, every specimen emitted a green glow. The light was visible mainly on the wings, hind limbs, and tail membranes.
The measured wavelengths ranged between 520 and 552 nanometres, a range the human eye perceives as green. Unexpectedly, the glow was found in all samples, across age, sex, and habitat, suggesting it may be a genetic expression instead of one influenced by environment.
What Produces This Bizarre Green Glow?
The glow, or photoluminescence, results when molecules take in ultraviolet light and emit it as visible light. It is found in plants, insects, and certain sea creatures but is not often observed in mammals. Using ultraviolet lamps and special filters, the scientists confirmed that the bats’ skin and wings produced genuine photoluminescence, not just reflected light.
Even century-old museum specimens displayed the same glow, suggesting it is a stable chemical feature passed down through generations. “It’s cool, but we don’t know why it happens,” said Steven Castleberry, professor of wildlife ecology and management.
Can Bats Actually See Their Own Glow?
The green wavelength fits perfectly within bats’ visual range, which spans 536 to 560 nanometres. This means bats might be able to see one another glowing in the dark. The researchers suggest it could help them communicate or identify each other during nocturnal flights.
“Bats have very unique social systems,” said lead author Briana Roberson. “It’s possible that glowing serves more diverse functions than we previously thought.”
However, no direct link to mating or camouflage was found. Bats from different habitats, including tree-roosting and cave-dwelling species, all glowed in the same shade of green. This uniformity suggests a common ancient origin more than an adaptation to the environment.
Did Bats Learn Glowing from Ancient Relatives?
Castleberry believes the glow could be a relic of evolution. “The data suggest all these species got it from a common ancestor,” he said. “It may have served a purpose long ago but doesn’t anymore.”
Similar traits have been observed in other mammals such as flying squirrels, marsupials, and platypuses. Scientists call this a synapomorphy—a shared inherited feature from a distant ancestor. The uniform green wavelength throughout species also favours this explanation.
The researchers also eliminated outside causes, including microbes or fungal infection. White-nose syndrome, the disease that produces glowing spots in infected bats, was discounted because specimens were too ancient and well-preserved for contamination.
What's Next for Bat Research?
The researchers plan to observe live bats later to see if the glow helps with flight or communication. They also plan to check if other mammals share similar light-emitting traits.
“While it’s still unclear if photoluminescence serves an ecological purpose, understanding its adaptive role could reveal more about bat behaviour and evolution,” said Roberson.
For now, the reason behind the eerie green glow remains unsolved. But the find demonstrates that even the most domesticated creatures of the night still have secrets to uncover.
The research appeared in the journal Ecology and Evolution.
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