Tree scorpions (Opisatacanthus asper) are about 100 mm long and live in bark crevices of large trees in Gorongosa National Park. They have a mild disposition and their sting is not harmful to humans. They are dark brown to black in color, and usually camouflaged in normal light. However, when illuminated with ultraviolet light, they fluoresce in a bright turquoise color that’s easily visible—even during the day. The function of this fluorescence is unknown although several ideas abound: one is that scorpions somehow use the fluorescence as an indicator of ambient light to help them find shady spots; another is that the ultraviolet light-reflecting compounds in the scorpion’s skin act as a sunscreen, and may be left over from the Devonian period when the ancestors of scorpions were more active during the day.
The scorpion was illuminated with an ultraviolet light source (commonly called a black light) and imaged using flash photography.
Image courtesy of Piotr Naskrecki PhD, Museum of Comparative Zoology, Harvard University, Cambridge, MA