The Glow Of The Desert Scorpion

By BRUCE LUND

Using black light flashlights, the kind available at local hardware stores, participants discovered lots of scorpions out and about at the Bat Night event held at the Moapa Valley National Wildlife Refuge a couple of weeks ago. This included the ‘glowing’ Hairy Desert Scorpion which is our largest scorpion and a common one in our area.

Just how scorpions manage to ‘glow’ is explained by the physics of fluorescence. Flourescence is where one kind of light radiation causes a chemical reaction that emits a different kind of light radiation. Thus when a black light (which emits ultraviolet radiation that is invisible to our eyes) is shone on this type of scorpion, it chemically reacts with a protein in the scorpion’s exoskeleton and emits the blue-green light (glow) which our eyes can see.

WHY scorpions ‘glow’ under the influence of ultraviolet light is a mystery that scientists are still trying to solve.

On the one hand, it may be that the glow is nothing more than chance – that scorpions simply possess a protein in their exoskeleton that reacts to UV light by fluorescing their blue-green color. If glowing had a function like helping scorpions to find mates (like flashing of the fireflies) or to attract prey (like some deep ocean fish), we would expect to see scorpions to turn on their glow at will. But they don’t.

On the other hand, we know that scorpions are most active at night, and that this is also when ultraviolet light is at its strongest from starlight and moonlight (the UV is still dim, but is stronger relative to other forms of light radiation). Since scorpions’ bodies fluoresce under ultraviolet light, scientists are trying to see if there is a connection.

One bit of evidence of a connection is that when scorpions were blindfolded by covering their eyes with foil, the scorpions remained inactive as if they could not detect whether it was dark or daylight. But when a black light emitting UV light was shone upon the blindfolded individuals, their bodies glowed and the individuals became active as if it was dark.

By this test, it seems that scorpions need and use UV light to ‘know’ when it is the right time to get out and hunt and do other things that scorpions do.

At this point, nothing has been concluded about any of this, and the search for answers goes on.

Bruce Lund is a retired biologist and has a lifelong love of nature instilled by his grandparents and some remarkable teachers. He has lived with his wife, Flo, in Moapa since 1997.