From a Wired Science article titled “Glowing Scorpion Exoskeletons May Be Giant Eyes“:
Scorpion bodies are studded with eyes, sometimes as many as twelve — and scientists may have found one more.
A scorpion’s entire exoskeleton may act as one giant light receptor, a full-body proto-eye that detects shadows cast by moonlight and starlight.
That’s still just a hypothesis, but it would help explain why they glow so brilliantly under ultraviolet light.
Twelve eyes? TWELVE! Little bastards.