Julián Faivovich at the Bernardino Rivadavia Natural Sciences Museum in Buenos Aires, Argentina, made the discovery unexpectedly while studying a pigment in the frog. "For some things we were planning on doing, we had to illuminate the frog tissues with UV light. Then we realised the whole frog was fluorescing," he says.He and his colleagues traced the fluorescence to a compound found in the lymph and skin glands. They found that this trait enhances the brightness of the frog by 19 per cent on a night with a full moon and 30 per cent during twilight.The fluorescent compounds absorb light at a wavelength at which frog photoreceptors have low sensitivity, and emit it in a wavelength at which they have high sensitivity. That means it's likely the frogs themselves can see the fluorescence.<snip>With around 5000 known species of frogs, it's unlikely that the polka-dot tree frog is the only fluorescent one."There's very few frogs that have a feature that's not found in any other frogs," says Blackburn. "So it probably is a trait that's more widespread, but then the question becomes what are the ecological circumstances that would drive fluorescence? Is it only common in tree frogs? Or is it ever found in other ecological circumstances?"