Scorpions: A glowing mystery

For a long time, I hear about the fact that "Scorpions glow under UV light", but I could never visualise that. Later, I saw some images from internet and got amazed seeing the glowing bluish-green scorpions. Finally, I got a chance to see the miracle in Goa last year. 
It was a monsoon time in July '14. After the evening snacks & tea, we chatted for a while waiting for the dark to fall. As light was eaten slowly by darkness, the calls of the frogs started rising gradually louder and louder. We said, its time to search for the night life, and headed to the field with our torches and cameras looking for subjects. 

While enjoying the sightings of frogs & geckos, we saw some scorpion holes in the mud walls on both sides of the pathway we were walking. The forest scorpions are usually found inside horizontal shaped holes in the vertical or slanting mud walls. We could hardly spot them, as they were shy against direct light. The moment we put the torch light on it, the scorpion moves inside the hole. 
Luckily this time, my friend had a UV torch and we thought we could see them if they glow or not. When we saw the mud walls with UV torch, we were shocked to see there were plenty of scorpions. They were everywhere - on the compound walls, on the electric poll pits, and on the mud walls. Their entire body was glowing in an unnatural neon blue colour, like a magic. With naked eyes (using normal torch), you cant even see them, but with UV torch, they were all glowing everywhere. We could see scorpions of all sizes - around 10-12 cm as well as many tiny young ones. 

A Scorpion glowing in UV light

An adult Scorpion with many tiny scorpions glowing in UV light

I was searching Internet to find the reason why scorpions glow under UV light. I didn't get any convincing answers though. Actually the answer for now is "no one knows the exact reason, why they glow under UV light". As per Internet, these could be the reasons, is what great scientists and biologists think.

Reference:
http://animals.mom.me/scorpions-glow-under-uv-light-7768.html

Their glowing bodies might serve as one big eye, helping scorpions find shelter under rocks, logs or grasses on moonlit nights, according to a 2012 study published in "Animal Behaviour." Led by Douglas Gaffin from the University of Oklahoma, this study showed that scorpions would scurry around in the dark until part of their bodies fell under the shadow of shelter. When shelter was scarce, scorpions preferred even a single blade of grass that cast just a small shadow to sitting completely exposed in the moonlight. This might be because the glowing exoskeleton helps the scorpions see by passing information to the brain on the amount of glow; when the exoskeleton glows more, the scorpion is in greater danger of predation. When there's no glow, the scorpion is sheltered from predators.

Scorpions don't have the best eyesight. They see mostly in the blue-green spectrum. In 2011, Carl Kloock of California State University began leading research on why scorpions glow. His research leads scientists to believe the glow might be an adaptation that allows scorpions to know when they've found safe shelter. Kloock studied the behavior of scorpions who could glow and those who had lost the ability. The glowing ones found shelter in the dark quickly, while those who couldn't glow tended to roam more.

Reference:
http://www.livescience.com/14155-full-moon-scorpions-glow-dark.html

California State University arachnologist Carl Kloock thinks otherwise. Over the past few months, Kloock and his colleagues have started unraveling the mystery of why scorpions glow.

"They may be using UV as a way to determine whether or not to come to the surface to look for prey, based on the light levels," Kloock told Life's Little Mysteries, a sister site to LiveScience.

Scorpions are nocturnal creatures. They abhor the heat and evaporative effects of sunlight, and it turns out they specifically avoid UV light too. In a recent issue of the Journal of Arachnology, the Cal State team reported that the arachnids adjust their activity level depending on the amount of UV shining on them. When flooded in UV, they are less active than when lights are dim.

"My thinking at this point for why they would respond to UV is that there is a UV component in moonlight," Kloock wrote in an email. If scorpions are hungry, he explained, they'll come out and hunt regardless of light levels. But if they're satiated, research shows they tend to lie low on moonlit nights, especially around the time of the full moon. "[Fluorescence] may be part of the mechanism by which the scorpions respond to moonlight," Kloock wrote. 

So the answer is yet to be discovered!