Most dangerous glowing animals

The most dangerous glowing animals are scorpions, all of which can glow, including the most venomous species, even though none of them is bioluminescent. Instead, scorpions are fluorescent, i.e. when ultraviolet light (invisible to the human eye) is shone upon a scorpion in the dark, visible light bounces back off it, yielding a blue glow that humans can see. What happens is that a special layer within the scorpion’s cuticle, known as the hyaline layer, contains substances that change the wavelength of the impinging ultraviolet light into the wavelength of visible blue light that duly reflects back. This layer is even present in scorpion fossils, so fossil scorpions fluoresce too if illuminated with ultraviolet light. The purpose of fluorescence in scorpions is currently unknown.