Bats found to glow bright green in ultraviolet light

Night hides more than soundless wings and high-pitched calls. It hides color too. Researchers from the University of Georgia have now found that some North American bats glow bright green under ultraviolet light.

The finding may look like a party trick, but it could reveal something deeper about how bats evolved and communicate.

Bats glow under UV light

Scientists at the Warnell School of Forestry and Natural Resources studied 60 museum specimens.

The specimens belonged to six species – big brown bats, eastern red bats, Seminole bats, southeastern myotis, gray bats, and Brazilian free-tailed bats.

Every specimen glowed green when exposed to ultraviolet rays. The glow appeared mostly on the wings, hind limbs, and tail membranes.

The measured wavelength of the light ranged from 520 to 552 nanometers. That is the same color range our eyes register as green.

Consistent glow across bat species

The researchers ruled out age, sex, and habitat as causes. The glow was consistent across all samples, hinting that the trait is genetic rather than environmental.

“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.

“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 glow happens

Photoluminescence happens when molecules absorb ultraviolet light and release it at a longer wavelength that we can see. Plants, insects, and marine creatures do this often. Mammals, not so much. The new study changes that assumption.

The team used ultraviolet lamps, special filters, and a light measurement tool to separate true photoluminescence from reflected light. The result was clear: the green light came from the bats themselves.

Their skin and wing membranes emitted it without any outside interference. Even century-old specimens glowed the same way. That stability points to a chemical trait passed through generations.

Can bats see the glow?

The green glow fits right into the visual range of bats. Many species can detect light between 536 and 560 nanometers. This overlap suggests that bats can probably see the glow. It might help them recognize one another or communicate during night flights.

“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. It’s possible for glowing functions to be more diverse than we previously thought,” noted study lead author Briana Roberson.

So far, no evidence links the glow to mating or camouflage. Bats that rest in trees and bats that roost in caves both glow in the same shade of green. If the light had evolved for hiding, the color would likely vary with habitat. Instead, the uniform glow points to a shared evolutionary origin.

Glow from ancient ancestors

“The data suggests that all these species of bats got it from a common ancestor,” said Castleberry. “It may be an artifact now, since maybe glowing served a function somewhere in the evolutionary past, and it doesn’t anymore.”

That idea fits broader studies on photoluminescence in mammals. Scientists have spotted similar effects in flying squirrels, marsupials, and even the platypus.

In many cases, the glow appears to be a leftover trait – a signal that once mattered but no longer plays a major role in survival.

Bats may share the same story. The glow might have once helped individuals locate each other in dim light.

Over time, echolocation took over as the main sensory tool. The visual signal faded in importance, yet the genetic code for it stayed.

Shared traits from common ancestors

Quantitative analysis from the study strengthens this theory. The consistent wavelength across all species points to shared chemistry.

Researchers call this a “synapomorphy” – a trait inherited from a common ancestor. It also shows that museum collections remain valuable. Old specimens still carry biochemical information that can answer new questions.

The team also checked whether microbes or surface changes might cause the glow. They found no signs of bacteria or fungi that emit light.

White-nose syndrome, a fungal disease known for causing glowing lesions in bats, was ruled out. The samples used were too old and clean for contamination.

Future research directions

“While it’s still unknown whether photoluminescence may serve an explicit ecological purpose, additional information on adaptive advantages it may provide could be valuable for further understanding bat behavior and ecology,” said Roberson.

Future research may focus on live bats. Observing them in motion could reveal whether the glow helps with flight coordination or social behavior. Scientists also plan to test if other mammals share similar emission wavelengths.

For now, the green shine remains a puzzle – a remnant of something ancient or a signal still waiting to be decoded. The study proves one thing: even in the dark, bats have secrets that light can reveal.

The study is published in the journal Ecology and Evolution.

Image Credit: Andrea Piazza

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