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.

“It might be a sort of alarm that’s always going off until the scorpion finds shelter,” said biologist Douglas Gaffin of the University of Oklahoma. “Shade might turn down the alarm on that part of their body, so they preferentially move in that direction.”

No matter their color in daylight, be it jet-black or translucent, ultraviolet light makes pigments embedded in their exoskeletons emit photons.

That property is called fluorescence, and nobody knows quite why scorpions possess it. Suggested explanations include mating signals or evolutionary leftovers of natural sunscreen needed before they became nocturnal. Whatever the case, 430 million-year-old fossils of scorpion relatives called eurypterids suggest their fluorescence has been around for a very long time.