Scientists Discover Fire Salamanders Glow and Ooze Fluorescent Slime

One rainy night in Spain, evolutionary biologist Bernat Burriel-Carranza pointed a UV flashlight at a fire salamander crossing a road, not really expecting much. What he saw stopped him in his tracks. The salamander's sides suddenly erupted in brilliant teal-colored speckles, glowing like tiny stars against its dark body. It was a discovery hiding in plain sight for centuries, on one of Europe's most well-studied amphibians. Scientists had been observing fire salamanders since the 1700s, and nobody had thought to check whether they glowed.

Fire salamanders are already pretty striking animals. Native to European forests, they wear bold yellow and black markings that serve as a natural warning to predators: back off, I am toxic. Scientists call this strategy aposematism, which is when a poisonous animal uses eye-catching colors or patterns to advertise its danger to potential threats. You can think of it like a skull-and-crossbones symbol on a bottle of cleaning chemicals. The bright pattern is not decoration; it is a life-saving signal. What the new research published in the journal Royal Society Open Science reveals is that the fire salamander's warning system might be even more sophisticated than anyone realized, adding an invisible-to-human-eyes glow to its already flashy appearance.

The glowing ability is called biofluorescence, which means the animal absorbs light at one wavelength, or color, and re-emits it at a completely different wavelength, usually producing brilliant greens, oranges, or blues. It is different from bioluminescence, which is when animals like fireflies or deep-sea fish actually produce their own light from scratch. Biofluorescent animals need an external light source, like UV light from the sun, to trigger their glow. UV light is a type of light energy present in sunlight that human eyes cannot detect, but many animals can. Under a UV flashlight in a dark forest, a biofluorescent creature can become startlingly visible.

Burriel-Carranza and his team went on to study fire salamanders in forests across Spain and Germany, photographing them under UV light and collecting samples of their skin secretions, the poisonous liquids their bodies produce. Out of twelve salamanders found in Spain's Catalonia region, ten showed vivid glowing spots concentrated on their sides, throats, and stomachs. Even more fascinating, every single secretion sample they collected glowed under UV light, including samples from German salamanders that did not have visible glowing spots. That glowing slime kept shining for at least 24 hours after collection. When the team examined thin slices of salamander tissue under a microscope, they found fluorescent compounds, special light-emitting chemicals, not just in the skin glands but also circulating through the salamander's bloodstream, meaning the glow is woven throughout the animal's entire body.

The scientists think this fluorescent display might serve two important purposes. First, it could supercharge the salamander's existing warning system. Other amphibians and many of their predators can see UV wavelengths that human eyes miss entirely, so a glowing toxic animal would be even harder to ignore than a non-glowing one. Second, it might play a role in mating. Male fire salamanders tend to have more yellow splotches than females, meaning they also glow more brightly. Males are also known to rear up and display their chests and throats during mating season, which happen to be exactly the areas where the fluorescence is most intense. Showing off a brilliant glowing chest might be a male's way of advertising his health and vitality to a potential mate, a bit like how some birds display bright feathers during courtship.

This discovery is part of a wave of biofluorescence findings across the animal kingdom. Over the past two decades, scientists have confirmed glowing abilities in pink squirrels, platypuses, sharks, and various amphibian species. Researcher Jennifer Lamb, a herpetologist, meaning a scientist who studies reptiles and amphibians, at St. Cloud State University, points out that each discovery helps fill gaps in our understanding of which animals fluoresce and why. Independent researcher Courtney Whitcher, who studies biofluorescence in treefrogs, puts it perfectly: discoveries are a product of what we look for. Fire salamanders have been studied since Swedish naturalist Carl Linnaeus formally named them in 1758, yet this glow went unnoticed until someone thought to bring a UV light into the forest. It is a reminder that even the most familiar creatures still have secrets to reveal, and sometimes all it takes is looking at them in a completely different light.

Source: National Geographic