Surprising discovery: The yellow-black fire salamanders show a previously unrecognized biofluorescence after irradiation with UV light – they glow turquoise. The belly and sides of the amphibians then show bright speckles, as biologists have discovered. This glow is apparently triggered by certain molecules in the skin glands, glandular secretions and blood of the animals. However, it is still unclear which molecules these are and what biological function this biofluorescence has for the fire salamanders.
Whether long-eared owls, geckos or polar bears: they all have the ability to biofluoresce. This afterglow occurs when molecules in skin, fur or feathers are stimulated by short-wave light or UV radiation. When they return to their basic state, these molecules release the excess energy as visible light – the animals glow. This fluorescence often lasts well into the night.
However, this subtle fluorescence often remains hidden to us humans because it is outshone by daylight or is too weak for us to notice. For this reason, biofluorescence has long been considered a peculiarity of marine animal species and arthropods in particular. Only recently have systematic tests revealed that many amphibians, reptiles, birds and mammals also biofluoresce.
With UV flash light for salamander stalking
Biologists have now also demonstrated biofluorescence in one of Europe’s most famous amphibians: the fire salamander (Salamandra salamandra). Although this yellow-black colored salamander is one of the best researched and studied amphibians, its fluorescence has so far remained hidden. “It is fascinating that such a well-researched species still harbors unknown phenomena,” says lead author Bernat Burriel-Carranza from the Natural History Museum in Barcelona.
Burriel-Carranza and his team only discovered the subtle glow of the fire salamander when they went on a very special salamander stalk in two forests in Spain and Germany: As soon as they spotted an animal, they triggered a UV flash light and photographed the amphibian with a special camera.
Brightly glowing speckles
The images revealed numerous greenish fluorescent spots on the fire salamanders’ skin. “This fluorescence was concentrated on the flanks and in the abdominal region of the salamanders, with the yellow-colored skin areas showing a higher density of light speckles than the black ones,” report Burriel-Carranza and his colleagues. “The strongest light emission was at wavelengths between 465 and 515 nanometers, which corresponds to a turquoise-green color.”
“Our observations prove that the fire salamander shows biofluorescence that is also visible to the human eye,” write the biologists. However, the glow is only strong enough for us if the salamanders are exposed to very intense UV light. “This shows us that even well-known creatures can keep secrets that only become apparent when they are examined using new methods,” says Burriel-Carranza.
The observations could also explain why the greenish fluorescence of amphibians has never been discovered before: under natural conditions, the excitation by UV light from the sun or moon is too weak to produce biofluorescence that we can see. Animals with high visual sensitivity to light, on the other hand, can perceive this cyan-green fluorescence even at low intensity.
The fluorescence is in the gland secretion
Further analysis showed where the fire salamander produces its fluorescence. During tests in the laboratory, the salamander’s skin glands and their secretions fluoresced particularly strongly. But the animals’ blood also glowed green when exposed to UV irradiation, as the biologists discovered. They therefore suspect that the causing fluorescence molecules circulate both in the blood and in the glandular secretions of the fire salamanders.
“The presence of this fluorescent compound was surprising because the skin secretions of salamanders have been studied chemically for decades and we were not aware of any published reports of fluorescence,” says co-author Andrés Brunetti from the Max Planck Institute for Chemical Ecology in Bayreuth. “We don’t yet know what compound this fluorescence is, but everything suggests that it is a molecule that was previously unknown in this species.”
What is the purpose of the glow?
It is also still unclear what biological function biofluorescence has in fire salamanders. “The fluorescence meets several criteria that indicate a communicative function,” explains co-author Martin Kaltenpoth from the Max Planck Institute for Chemical Ecology. “It could help salamanders sense each other at night or in particularly dense environments.”
It would also be conceivable that the fluorescent glow should complement and reinforce the warning costume of the fire salamander. Its striking yellow-black coloring signals to potential predators that this amphibian contains poisonous secretions and is inedible. The biologists suspect that biofluorescence may be used to transmit this warning signal at dusk or at night. They hope that chemical identification of the fluorescent dye will provide more answers. The team is already in the process of carrying out the necessary analyzes.
Source: Bernat Burriel-Carranza (Museu de Ciències Naturals de Barcelona) et al., Royal Society Open Science, 2026; doi: 10.1098/rsos.251991