Scorpions have a protein in their exoskeleton that reflects UV rays, making them glow.
If you have ever gone in your backyard in the summer, in the evening with a black light, you have probably noticed the scorpions glowing on the wall, the reason they glow is because they have proteins in their exoskeleton that reflects that UV ray.
An interesting theory behind the magical glowing protein is a belief that the protein allows scorpions to sense UV rays. Spiders don't have a nervous system like you or I. They can't feel the heat of the sunlight to know when it's shining upon them. So many scientist believe this protein triggers something allowing the scorpion to detect when it is exposed. And while not conclusive, scorpions will move out of the black light's beams.