Friday, June 28, 2013

Glowing Scorpions

Photo credit: Cowyeow/Flickr

Scientists now believe that scorpions’ fluorescent exoskeletons may help them to find cover during the night.

The scorpion’s cyan-green glow can be attributed to two chemicals, noharmane and hymnecromone, that are deposited in the exoskeleton during sclerotization, a biological process by which arthropods are able to harden their exoskeletons. Interestingly, neither young nor recently molted adults fluoresce when exposed to UV light. Juvenile scorpions eventually develop the trait as they mature. Adults regain their fluorescence as their exoskeleton re-hardens as part of the molting process. In the picture below, you can also see that the scorpion’s old exoskeleton continues to fluoresce (Photo credit: skinheaddave/ 

Scorpions have been known to glow under UV light for quite some time, but no one has known why until just recently. One idea was that the fluorescence had no real function, and that it was just a chemical byproduct of the scorpion’s exoskeleton formation. Another hypothesis proposed that the fluorescent compounds were an evolutionary leftover from when scorpions were active during the day and might have benefited from a natural “sunscreen”.  Others have suggested that fluorescence could help to attract prey, deter predators, or to help find mates.

Photo credit: D. Finnin/AMNH

Douglas Gaffin and his lab at the University of Oklahoma came up with a new explanation. They found that scorpion eyes and photoreceptors in their head and tail are most sensitive to the same wavelengths of light that are emitted by their fluorescing exoskeletons. As it turns out, scorpions happen to be active during the early evening when ultraviolet light becomes more abundant than other wavelengths of light. When exposed, scorpions’ exoskeletons fluoresce, and the fluorescence is detected by their eyes and photoreceptors. This allows scorpions to tell when they are vulnerable to predators and when they are safely hidden. Gaffin’s lab at the University of Oklahoma is now trying to determine whether the scorpions can detect UV light directly.

To read Douglas Gaffin’s report:

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