In the humid forests of Europe, an animal that scientists have studied for decades is glowing turquoise in the dark—if you have the right light to see it. The fire salamander, instantly recognizable by its bold black and yellow striped pattern, harbors a hidden secret: it is biofluorescent, emitting a striking cyan-green light when exposed to ultraviolet radiation. An international research team has just revealed this phenomenon in the journal Royal Society Open Science, a discovery that underscores how much we still have to learn about even the most familiar creatures.
This matters because biofluorescence—the ability to absorb UV light and re-emit it as visible light—was long thought to be confined to the ocean depths. In recent years, scientists have found it cropping up in terrestrial reptiles, birds, and amphibians, reshaping our understanding of how animals communicate and defend themselves. That fire salamanders possess this trait, despite centuries of observation and decades of intensive research, is humbling. It is a reminder that new tools and fresh perspectives can reveal secrets hiding in plain sight.
The research team, led by scientists from the Natural History Museum of Barcelona, the Institute of Evolutionary Biology of the Spanish National Research Council (CSIC), Pompeu Fabra University in Barcelona, and the Max Planck Institute for Chemical Ecology in Jena, discovered that the biofluorescence is concentrated in the salamander's ventral yellow areas and along its sides. More remarkably, the fluorescence originates from the skin glands and their secretions—compounds that maintain their glowing capacity for more than 24 hours after being released into the environment.
"It is fascinating that such a well-studied species still harbors unknown phenomena like this," says Bernat Burriel, researcher at the Museum of Natural Sciences in Barcelona and first author of the study. "It reminds us that even the most familiar organisms can hide secrets that are only revealed when they are observed with new tools."
The ecological purpose of this glow remains speculative but tantalizing. The cyan-green fluorescence could help salamanders locate each other in the darkness of nocturnal or densely vegetated forest environments. Interestingly, full moonlight contains more UV and violet wavelengths than daylight, which may mean salamanders are increasing their visibility to each other by adding fluorescent speckles to their already vivid yellow skin. The glow could also reinforce the salamander's warning signals to predators—a defense strategy that these toxic amphibians have relied on for over a century. The fire salamander's skin secretions contain samandarines, a group of highly toxic alkaloid compounds, and the presence of fluorescence in these poisonous secretions opens new questions about how predators perceive threat.
Martin Kaltenpoth, director of the Department of Insect Symbiosis at the Max Planck Institute, notes that visually oriented animals with high sensitivity could perceive this fluorescence at low intensities. Humans, by contrast, can only see it with the aid of a UV lamp. Yet in the salamander's world of nocturnal forest floors, where starlight and moonlight reign, such adaptations may be profoundly important.
The fire salamander is listed as vulnerable by the International Union for Conservation of Nature, threatened by habitat degradation and fragmentation. These discoveries of hidden traits deepen our responsibility to protect these animals and the complex ecosystems they inhabit. As Burriel's work shows, there is always more to learn.