It's called being bioluminescent. When UV light is shined on a scorpion it glows! Scorpions are the most active just after sunset, which the only time when UV light is more prevalent in the sky than the colors we can see. They also only have one light detecting pigment in their eyes, which is tuned to only blue-green. But otherwise, there are no confirmed scientific theories for why scorpions are bioluminescent - which is fascinating!
One theory is that they glow under UV light, to turn the dim UV light into a color that they can see. Another theory is that it's part of their evolution that either helps with them luring prey, or to help other animals avoid them. Yet another theory is that production of the two chemicals that glow are just a coincidence. So no one really knows - but it's amazing!
And what's even more fascinating is that scorpions are not the only bioluminescent creature on this planet. But that's a topic for another day....
