Archivists who work in museums must be very bored. Who would think of placing taxidermied specimens from 1922 under ultraviolet light to see what happens? But the scientific spirit knows no bounds, and it ended up surprising a team of researchers in Georgia, USA. Imagine their surprise when they exposed old bat specimens to an ultraviolet (UV) lamp… and the little animals lit up with an intense green glow. Almost a century had passed and no one had realized that bats had fluorescent wings and legs, a biological secret that had been hidden for decades.
The finding, published in 2025 in the journal Ecology and Evolution, reveals that this is not only an extremely rare genetic trait, but also an intrinsic characteristic of six common species of North American bats. Although they have discovered that they glow in the dark… they still don’t know exactly why.
Studying biofluorescent bats
The research team, led by Brianna J. Roberson, analyzed more than 60 specimens from the museum to verify the consistency of the phenomenon. (Perhaps to make sure that some prankster hadn’t painted them with biofluorescent paint in the 1980s.) However, the green light comes from the animals themselves. The curious thing was the persistence of the glow over time; specimens preserved since 1922, more than a century ago, glowed exactly the same as specimens cataloged much more recently.
This suggests that the chemical compound responsible for this glow under UVA rays is extremely stable and is integrated into the tissue structure. Ultimately, photoluminescence occurs when a molecule absorbs short-wave energy—in this case, ultraviolet light. Immediately afterwards, this molecule releases that same energy in a longer wave than is visible.
Not only were the bats green, but researchers discovered that the color was uniform across all six species.
Males and females, young specimens and century-old specimens all had the same uniform green color, with an average wavelength between 520 and 552 nanometers.
Why do these bats glow?
Despite research, the biological function of this glow remains a mystery to scientists. For now, scientists are considering two main hypotheses to explain this unique trait.
On the one hand, this green light falls within the color range that bats themselves can detect visually. Historically, we have thought that bats were practically blind and only oriented themselves inside caves and outside by echo. However, with this green light, it seems that they can see and communicate with each other within the same species. Perhaps it helps them recognize their mate, identify their territory, or simply orient themselves within the colony in which they live.
The second hypothesis is that it is simply an evolutionary vestige. Perhaps it was a characteristic that was useful for a common ancestor of the six species, but over time it lost its adaptive function. As this trait does not pose a disadvantage for survival, it has been inherited over generations without being erased from the gene pool.
However, these two hypotheses do not hold up very well, mainly due to the lifestyle of these animals: after all, bats live in environments with very little UV radiation, such as caves, mines, and tree hollows. Without sufficient natural ultraviolet light, this glow will probably never manifest itself outside the laboratory, so its usefulness is debatable. For now, scientists will move on to researching live bats and measuring ultraviolet radiation in their shelters to try to solve the mystery.
Which North American bats are bright green?
The six species belong to the Vespertilionidae and Molossidae families. Lasiurus borealis (Eastern red bat) and Lasiurus seminolus (Seminole bat) are mainly arboreal species. Eptesicus fuscus (Big brown bat) is one of the most common and adaptable species, often found in buildings and urban areas.
Tadarida brasiliensis (Brazilian free-tailed bat) is famous for forming massive colonies that can house millions of individuals. Myotis grisescens (grey bat) is a federally endangered species.
This animal depends on caves throughout the year, both for hibernation and for giving birth. Myotis austroriparius (Southeastern Myotis) also uses caves and cavities in large trees such as cypress.
So now you know, if you need inspiration for Halloween decorations next year, you can always buy a few plastic bats and paint them fluorescent green… If anyone asks, you’re just being true to their biological anatomy!