Split-screen shot showing emperor scorpions (Pandinus imperator) in visible light (left) and ultraviolet light (right) in this laboratory demonstration of fluorescence. While a number of arthropods fluoresce, including some insects and spiders, it is especially pronounced among scorpions and whip scorpions (vinegaroons). It is unsure if the fluorescence has a useful purpose or is just a random act of evolution. The emperor scorpion is native to much of Africa and can reach 20 centimetres in length.