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Image Credit: National Park Service

The mystery behind a scorpion's glow

  • BY Angela Heathcote |
  • July 03, 2017

You might not be aware that scorpions glow, but it’s a phenomenon that’s long puzzled experts.

SCORPIONS FLUORESCE when exposed to ultraviolet (UV) rays, producing  a bright blue -green light that emanates from a layer within their exoskeleton.  As for why scorpions glow, that’s been a subject of fierce speculation that continues to bewilder scientists.

Some have argued it helps improve their ability to hunt or may help protect them from being hunted.  Others say the bright hues could be a part of an elaborate mating strategy. However, the most convincing theory yet comes from Victorian scientists who propose that that a scorpion’s entire body acts as an ‘eye’ to sense UV.

“If the whole of the body is sensing UV it means that the whole of the animal is exposed to predation, whereas if there is no UV on the body then it knows it is under a shelter,” Ken Walker, the senior curator of entomology at Museums Victoria, told Australian Geographic.

Being ambush predators, scorpions don’t like to move around much when targeting prey.  

“If they’ve got to move around to see whether they are in shade or under cover, they are probably going to expose themselves to anything that they’re trying to catch,” Ken explained. “You can get UV from the Sun but also the Moon, which is the reflection of the Sun and the Moon. It appears that because the whole of the body of the scorpion fluoresces, the theory is that whole of the scorpions’ body acts like an eye.”

This fluorescent layer of the scorpions’ exoskeleton is subject to change during periods of moulting, when  their outer ‘shell’ becomes very soft. Ken said it takes about 90 minutes for this outer layer to harden. After analysing this transition of the scorpions’ exoskeleton, scientists gained unique insights into the scorpions’ fluorescence

“During that hardening, they don’t fluoresce.  It’s only when they’re hard,”  Ken said. “There’s a chemical in the cuticle that causes it to fluoresce and that chemical isn’t there just after they moult.

“Imagine if a scorpion had just its tail underneath a leaf that was protecting it but the rest of the body was out in the open, then if the whole of the body acts like an eye it would realise that its tail is being protected. Being under a leaf, the tail wouldn’t fluoresce because it doesn’t get the moonlight UV. It can sense how much of its body is protected.”

Despite being the most reasonable explanation yet, however, our understanding of why scorpions glow still remains a mystery. 

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