The salamander is a widely known animal in Europe, easily identifiable by its unmistakable black and yellow pattern and by the toxic secretions it uses as a defense mechanism. The International Union for Conservation of Nature (IUCN) lists the salamander as “vulnerable” on its Red List of Threatened Species. It is affected by the degradation and fragmentation of its habitats, and can be found mainly in humid forests, streams and mountain areas.

The study, published today, reveals that under ultraviolet light, the salamander displays distinctive fluorescent patterns. Specifically, it emits a turquoise glow on its ventral side and along its flanks, matching the distribution of its skin glands and poisonous secretions.

The team also discovered that compounds in the salamander’s blood and granular glands also glow, suggesting a systemic distribution of fluorescent molecules, a rare trait previously only known in tree frogs.

Although the ecological significance of this phenomenon remains uncertain: the fluorescent glow may serve a communicative function and be involved in courtship, migration, or predator warning.

An amphibian that glows at night in the forest

The study reveals that this biofluorescence is mainly concentrated in the ventral yellow area and on the sides of the body. Specifically, it originates mainly from the skin glands and the secretions they produce, which can maintain their fluorescent capacity for more than 24 hours after being released.

"It is fascinating that such a well-studied species still harbors unknown phenomena like this. It reminds us that even the most familiar organisms can hide secrets that are only revealed when they are observed with new tools," says Bernat Burriel, researcher at the Museum of Natural Sciences in Barcelona and first author of the work.

When it receives ultraviolet light —imperceptible to the human eye—, chemical substances present in the salamander’s skin transforms it and emits it back into the visible spectrum, manifesting a striking coloration in green and cyan tones. This phenomenon, called biofluorescence, differs from bioluminescence because it depends on an external light source. By contrast, bioluminescent organisms, such as fireflies, generate their own light through chemical reactions.

For many years, biofluorescence was considered to be limited to marine environments, with scorpions being a rare exception. However, a series of recent discoveries has revealed that it is also common in terrestrial environments, with reports in several groups of animals, including reptiles, birds, and amphibians.

What is the purpose of biofluorescence, and what substance causes it?

The results suggest that biofluorescence may have significant ecological functions. For instance, it may facilitate communication among individuals, influence the selection of a mating partner, or reinforce warning signals against predators.

"Fluorescence meets several criteria that suggest a communicative function. It could help salamanders detect each other in nocturnal or particularly dense environments, or act as an additional defense signal," says Martin Kaltenpoth, the director of the Department of Insect Symbiosis at the Max Planck Institute for Chemical Ecology and co-author of the study. In addition, the fact that it is found in toxic secretions also opens up new hypotheses about its role in interactions with other species.

The specific role of fluorescence in fire salamanders is still speculative. However, visually oriented animals with high sensitivity could perceive this cyan-green fluorescence at very low intensities. Humans, on the other hand, can only see this fluorescence with the aid of a UV lamp. In a forest at night, the only light that reaches the ground where salamanders live comes from the stars and moon. Interestingly, full moonlight contains more UV and violet wavelengths than daylight, which has a relatively homogeneous distribution of wavelengths. Therefore, salamanders may increase their visibility to each other by adding cyan-green speckles to their yellow skin.

The salamander’s natural fluorescence may also be part of an aposematic signaling strategy. This is when animals exhibit visible warning colors to alert predators that they are toxic.

The link between warning coloration and toxic compounds was first established in salamanders more than a century ago with the discovery of samandarines, a group of highly toxic steroidal alkaloids originating from cholesterol precursors. “The presence of this fluorescent compound was surprising because salamander skin secretions have been studied chemically for decades, and we were unaware of any published reports on fluorescence,” says Andrés Brunetti, a researcher at the Max Planck Institute for Chemical Ecology and co-first author of the study.

"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. Identifying it will be key to understanding its origin and function," adds Salvador Carranza, researcher at the IBE (CSIC-UPF) and also co-author of the study. The researchers are currently in the process of chemically characterizing candidate compounds.

Implications for research and conservation

The discovery expands knowledge about amphibian biology and highlights the importance of studying organisms from new perspectives. It can also have implications for conservation, as better understanding the mechanisms of communication and behavior can help protect vulnerable species.

This study, in which researchers from the Institute of Subtropical Biology and the Catalan Society of Herpetology have also participated, is part of a pioneering amphibian conservation project in Catalonia funded by the Barcelona Zoo Foundation.

Referenced article:

Burriel-Carranza, B.; Brunetti, A. E.; Skamnelou, M.; Escudero, J.; Estarellas, M.; Tulloch, S; Riaño, G.; Rivera, X.; Piulachs, M.-D.; Engl, T.; Weiss, B.; Kaltenpoth, M.; Carranza, S. (2026). Glandular biofluorescence in fire salamanders (Salamandra salamandra): first evidence and ecological implications. Royal Society Open Science 13: 251991. https://doi.org/10.1098/rsos.251991