Why do scorpions floresce under UV light? No one knows. But we know how they floresce, though you'll slap your forehead when I tell you because it's so obvious. It's because of the Beta carboline and 7-hydroxy-4-methylcoumarin that emerges in the hardening cuticle of their exoskeletons of course.

Newly molted scorpions don't floresce, so the florescing compounds have to be either secreted by the scorpions or else somehow develop as part of the tanning process. We just don't know. Of course, I imagine scorpions are asking each other why the rest of us don't floresce. We must look so boring to them, what with our visible light band affinity.
Thanks for the photo, Mike.