U is for Ultraviolet Fluorescence

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As a part of the A-Z Photographic Glossary of Biological Terms challenge, today it is U for Ultraviolet Fluorescence as illustrated by this pair of Brown Bark Scorpions (Centruroides gracilis; Butidae; female below, male above) photographed under UV light, from the Sittee River Wildlife Reserve, Stann Creek.

With the exception of some species of the family Chaerilidae, as far as is known all other species of scorpion fluoresce under UV light.

Scorpions are nocturnal animals, feeling vulnerable in the daylight. When exposed to ultraviolet (UV) their exoskeletons glow blue-green, but scientists aren’t exactly sure why. There are a number of theories but the consensus now seems to be that their glow helps scorpions find shelter in their dark environments.

While we normally associate UV light with daylight, the rays responsible for tans and sunburn, at night a certain amount of UV light is reflected off the sun onto the moon (the moon’s glow is “borrowed” light) and can fluoresce scorpions that are exposed in the open at night.

This pointed the way for a team at the University of Oklahoma, led by Doug Gaffin, to investigate what happened when scorpions’ eyesight was blocked in the presence of UV light. The results of their work showed that fluorescence under UV light helped scorpions detect whether they were under shelter or exposed at night. They determined that their exoskeleton functions as a whole-body photon collector allowing scorpions to detect shelter.

The same female Brown Bark Scorpion pictured above, but in normal light:

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and the the male under normal light:

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