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1 min read Nature

An Amphibian’s Poison Glows Blue-Green

A blacklight on a rainy road in Spain gave it away. The same compound runs through the animal's blood, and nobody could identify it.
Field Notes

Field Notes

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Point an ultraviolet flashlight at a fire salamander and its yellow spots answer with a speckled blue-green shimmer. The species was described more than two and a half centuries ago and ranks among Europe's most thoroughly examined amphibians. Nobody had noticed the glow.

The trait is called biofluorescence. An animal absorbs light of one wavelength and sends it back out at another. (Bioluminescent creatures generate light chemically; fluorescent ones have to borrow it.)

Bernat Burriel-Carranza, who studies evolution at the Natural Sciences Museum of Barcelona, had taken to carrying a blacklight on night fieldwork. One wet evening in Spain, he aimed it at a salamander on a road, and its flanks lit up.

From April 2024 to November 2025, his team photographed these 6- to 12-inch (15- to 30-centimeter) animals under UV at sites across Spain and Germany. The glow appeared to originate chiefly in the yellow markings, heaviest along the sides and belly. Swabs of their toxic skin secretions fluoresced too, hinting that the poison glands are involved. Two dissected, preserved specimens held fluorescent compounds inside those glands and also in the blood, so the substances may circulate through the body, a pattern documented before only in certain tree frogs. The study did not identify the molecule itself.

Why glow? The researchers offer two ideas. Full moonlight carries proportionally more violet and ultraviolet than daylight, and the most moonlight filters down to the woodland floor in autumn, the salamanders' usual breeding season. The shimmer could help salamanders find one another in the dark. Or it could reinforce the warning already painted on those yellow spots.

An animal named for fire does glow after all. The color is wrong, and the flashlight is not included.

Read the full story at Smithsonian Magazine, June 5, 2026

Hot Take: A blacklight is about the cheapest instrument in field biology. Every species filed as thoroughly known deserves one evening with it before anyone closes the file.

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