An Iconic Salamander Has Been Hiding A UV Glow For Centuries

Fire Salamanders Glow Under UV Light, and the Source Is Their Own Toxic Skin

Europe’s most iconic salamander has been hiding something in plain sight for centuries. Under ultraviolet light, it lights up blue-green. Scientists have now traced that glow to the same skin secretions involved in the salamander’s chemical defense, though the specific glowing molecule has yet to be identified.

Fire salamanders are hard to overlook. Jet-black bodies splashed with bold yellow markings have made them one of Europe’s most recognizable amphibians, a fixture in natural history going back centuries. Scientists have studied them obsessively, cataloging their poisons, their breeding habits, their warning colors. Yet one trait of these animals had never been formally documented until now. A team of researchers has discovered that fire salamanders glow under ultraviolet light, producing a blue-green shimmer concentrated along their flanks, belly, and throat. Published in Royal Society Open Science, the finding raises questions about whether the glow plays a communicative role.

Biofluorescence, the ability to absorb UV or violet light and re-emit it as visible light, has been turning up in more and more animals in recent years, from sharks and parrots to chameleons and tree frogs. Fire salamanders have their own version, and it appears rooted in the glands that produce their skin secretions. That secretion keeps glowing even after it leaves the animal’s body, persisting on surfaces like moss for at least 24 hours.

Fire Salamanders’ Glow Traced to Toxic Skin Glands

Researchers surveyed fire salamanders at sites in Spain and Germany between April 2024 and November 2025. Working in forested areas of Catalonia, the community of Madrid, and Waldeck Forest in Thuringia, Germany, the team examined dozens of animals under a UV flashlight.

Of 12 adults encountered in Catalonia, 10 displayed obvious glowing speckles visible to the naked eye. In Germany, three of 23 animals showed similar patterns. Two individuals from Madrid showed no speckles at all, though the researchers note that sampling there was limited. No larvae displayed any external glow, which the team suggests may be because the responsible glands haven’t fully matured in younger animals.

Cameras fitted with specialized filters confirmed the glow concentrated on the belly and sides of adults. Yellow skin patches consistently showed more glowing speckles than black ones. Despite sharing the same gland types, the back showed no visible glow, which the team attributes to a thicker layer of dark pigment absorbing or blocking emitted light before it reaches the surface.

When researchers stimulated the animals to release secretions, those secretions glowed under UV light in both blue and green wavelengths.

Fire Salamander’s Glow Detected in Both Poison Glands and Blood

To find the source, the team examined thin tissue slices from preserved specimens under high-powered microscopes. Strongest emissions came from two gland types: smaller glands distributed across the body, and a raised pair behind the head that releases secretions when the animal is threatened.

A separate technique measured how long the glow persists at the molecular level after light triggers it, a detail that helps distinguish between different light-emitting molecules. Glandular secretions showed a timing pattern nearly identical to that of the animal’s blood. This points to, but does not prove, the possibility that a similar light-emitting compound is shared between the blood and the glands. Such a link has previously been described only in tree frogs.

That compound’s identity remains unknown. Salamander secretions are well-studied, but the main known toxic chemicals in them are not fluorescent. Whatever is producing this light is likely a molecule that hasn’t been identified in this species before.

Fire Salamander Fluorescence May Serve as a Nocturnal Signal

Fire salamanders are nocturnal animals that live in deciduous forests and breed in autumn. At night, under moonlight, available light shifts toward UV and violet wavelengths, exactly what triggers the salamanders’ glow. Mossy forest floors produce a contrasting red glow from plant material under UV light, meaning a salamander’s blue-green emissions would stand out visibly against the background. Many amphibians also have eyes tuned to low-light conditions, with cells sensitive to blue and green wavelengths, matching what fire salamanders emit.

During the breeding season, males have been observed adopting a raised posture with their head lifted and front limbs extended. Researchers note this behavior prominently exposes the throat, one of the areas where glowing speckles are most concentrated. Males also tend to carry more yellow coloration than females, and since the glow is stronger in yellow patches, the team speculates that fluorescence could play a role in mate signaling. Whether it actually does has not been tested.

Four other salamander and newt species surveyed during the fieldwork, including marbled newts, palmate newts, Pyrenean brook newts, and Iberian ribbed newts, showed no comparable glow, suggesting this trait is not shared across related species.

For all the centuries people have watched fire salamanders, this UV-lit glow had never been formally documented. That oversight stands as a reminder that even thoroughly studied animals can still yield genuine discoveries, especially when someone thinks to try a different tool.

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