Scientists Have Been Studying Fire Salamanders for More Than 250 Years. They Just Discovered That the Creatures Glow Under UV Light

Fire salamanders—one of Europe’s most well-researched amphibians—are biofluorescent, which means they can absorb light from an external source at one wavelength, then re-emit it at another

Sarah Kuta | Daily Correspondent

June 5, 2026 11:09 a.m.

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First described more than 250 years ago, fire salamanders are among the most-studied amphibians in Europe. Yet researchers are still making new discoveries about these charismatic creatures. Most recently, scientists learned that fire salamanders emit a bluish-green glow after being exposed to ultraviolet light, wavelengths that humans usually can’t see.

It’s the first time the phenomenon, known as biofluorescence, has been documented in the species, researchers report in a study published May 27 in the journal Royal Society Open Science. Though the ecological functions of biofluorescence remain unclear, scientists suspect that the amphibians might use the glow to communicate with one another, select mates or ward off predators.

Biofluorescence occurs when organisms absorb light from an external source at one wavelength, then re-emit it at another. Scientists used to think that only marine creatures and arthropods—a group that includes insects and arachnids—were biofluorescent. But in recent decades, they’ve been finding the trait in more animals, including some reptiles, birds and amphibians.

“We are in a thrilling period of discovery in terms of biofluorescence in amphibians and other [four-limbed vertebrates],” Jennifer Lamb, a biologist at St. Cloud State University who was not involved with the research, tells National Geographic’s Jack Tamisiea.

Studies like this one, she adds, “help fill some of the gaps in our understanding, both in terms of what species fluoresce and in terms of the mechanisms likely responsible for that fluorescence.”

Against this backdrop, Bernat Burriel-Carranza, an evolutionary biologist at the Natural Sciences Museum of Barcelona, decided to start taking an ultraviolet (UV) flashlight, also known as a blacklight, with him on evening field expeditions. On a rainy night in Spain, he spotted a fire salamander crossing the road and pointed the beam at it. The flashlight revealed a bright, speckled pattern along the creature’s flanks.

Common throughout Europe, fire salamanders are small, black-and-yellow amphibians that range from 6 to 12 inches long. These nocturnal critters tend to live in cool, damp forests near bodies of water, where they feast on worms, slugs and other insects. If they feel threatened, fire salamanders can protect themselves via toxins in their skin or by spraying poisonous liquid from glands behind their eyes. They breathe through their skin, can regrow their limbs and tails and give birth to live young.

After the initial field observation in Spain, Burriel-Carranza and his colleagues decided to investigate biofluorescence in fire salamanders further. Between April 2024 and November 2025, they searched for fire salamanders in Spain and Germany, illuminated them with a UV flashlight and took photographs to capture the bright, speckled glow. The fluorescence seemed to be coming mostly from the yellow spots on the creatures’ skin and concentrated along their sides and stomachs.

Researchers also swabbed the salamanders’ skin to collect samples of their toxic secretions. When they exposed the slime to UV light, it glowed, too, suggesting the biofluorescence may be coming from the glands that produce the poisonous goo.

To confirm that hypothesis, the team dissected two preserved fire salamanders. When they looked at tissue samples under a microscope, they found fluorescent chemical compounds in the glands and bloodstream, which suggests the substances circulate throughout the creatures’ bodies. That’s something that had previously been observed only in some tree frogs, which use fluorescent compounds known as hyloins to illuminate their translucent skin.

“We still don’t know what the compound responsible for this fluorescence is, but everything indicates that it is a molecule unknown until now in this species,” says study co-author Salvador Carranza, a biologist at the Institute of Evolutionary Biology in Spain, in a statement. “Identifying it will be key to understanding its origin and function.”

Though humans usually need a UV light to see the salamanders’ blue-green glow, it might be more clearly visible to other animals. Because salamanders are nocturnal and live in dense forests, one possible explanation is that they fluoresce so they can see one another better at night. The researchers say this proposal is supported by the fact that, compared with daylight, full moonlight contains more UV and violet wavelengths, the ones that are absorbed by the animals and re-emitted at different wavelengths. Additionally, the amount of moonlight that reaches the forest floor peaks in the fall, when the salamanders usually breed.

Beyond flagging down potential mates, the amphibians might also be using their natural fluorescence as a warning to predators. The scientists think the creatures use their bright yellow splotches as natural “keep away” signs, and because the fluorescence is concentrated in those markings and their toxic secretions, it may help reinforce that warning.

No matter how fire salamanders use their biofluorescence, Burriel-Carranza finds it “fascinating” that such a well-studied species could still hold undiscovered traits, he says in the statement.

“It reminds us that even the most familiar organisms can hide secrets that are only revealed when they are observed with new tools,” he adds.

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Sarah Kuta is a writer and editor based in Longmont, Colorado. She covers history, science, travel, food and beverage, sustainability, economics and other topics.