07/21/2017 Scorpions, Sting and Shine

This South Texas species of scorpion emits a blue-green glow under a “black light.” The purpose of this ability to fluoresce is unknown and is still being investigated. Some of the world’s 1500 species of scorpions have potentially fatal stings. Fortunately, the scorpions in Texas have “relatively mild” venom. Robert Benson photo.

Scorpions, Sting and Shine (Karen Benson)

Most of us have an ingrained respect, if not outright fear, of scorpions.  If you have ever experienced a scorpion’s sting, that fear is understandable!  Once stung, twice shy!

Scorpions are fascinating animals, however.  If you can suspend your dislike for a bit, you may be very impressed.  For instance, did you know that they can glow in the dark?

Yes, indeed!  In fact, one of the easiest ways to find a scorpion is to go out at night with a “black light.”  Ultraviolet light rays cause the exoskeleton of a scorpion to fluoresce. The Internet says all scorpions can fluoresce and that they give off a pretty, blue-green glow.

Scientists first learned about the ability of scorpions to fluoresce in the 1940s.  It seems to be due to a certain chemical in the outermost layer of the exoskeleton.  The substance absorbs the high frequency wavelengths of UV light.  It then converts and re-emits them as lower frequency wavelengths in the blue-green color range.  Newly molted scorpions do not fluoresce, nor do newly hatched babies.  It seems the chemical develops over time in the cuticle of the exoskeleton.

The big question was why do they fluoresce?  Scientists did not agree on the purpose of this phenomenon.  Some suggested that the glow helped the scorpions find mates.  Other researchers thought that the fluorescence dazzled prey, making it easier to catch.  One hypothesis was that the “light conversion effect could act as a sunscreen.”  However, none of these hypotheses held up under the scrutiny of experimental investigation.  A few arachnologists even suggested that the ability was functionless, that it is just a random result of evolution.

Recently, Dr. Carl Kloock at California State University noticed that scorpions are reluctant to come out on moonlit nights (unless they are extremely hungry).  Scorpions are nocturnal.  They abhor sunlight with its high-energy UV rays.  Even moonlight has a small component of ultraviolet light, (they say), although I think it must be negligible.  Nevertheless, the Internet claims scorpions can fluoresce in bright moonlight.  The researchers at Cal State hypothesize that the fluorescence might be a mechanism to help them detect UV light and to diffuse it.  If this true, then the ability to fluoresce IS like a sunscreen!  More studies are obviously needed to test this hypothesis.

Scorpions have had a long time to evolve.  They are quite ancient, dating back 440 million years, when their ancestors were aquatic.  Some of these ancestors were more than a foot long—how horrible is that?  Nowadays, they are smaller and land dwellers, but the basic body plan is unchanged:  A pair of pincers in the front, eight legs, and a barbed tail that injects venom.

A scorpion’s prey is primarily other arthropods such as insects and spiders.  They use those pincers to grab prey.  They then inject the prey with the venom to immobilize or kill it.  Of course, they also use that venom to defend themselves (much to our pain).  The 1,500 or so species of scorpions around the world have different potencies to their poison.  “A complex cocktail of neurotoxins, organic compounds, and tissue-penetrating enzymes, scorpion venom varies in potency from relatively mild to excruciatingly painful, even potentially deadly.”  Fortunately, all Texas scorpion species are considered to have “relatively mild” venom.  But it won’t feel that way!

Mexico is a different story.  Their species are much more dangerous.  Texas Parks and Wildlife warns “Scorpions sting an estimated 100,000 people a year in Mexico, resulting in up to 800 deaths annually.”  You may want to travel with an epi-pen!   The Arizona Bark Scorpion (Centruroides exilicauda) is the only United States species reported to have caused fatalities.

The good thing for us is that the scorpions’ ability to fluoresce is that we have an easy way to detect them in our homes.  A quick survey of your bedroom with an LED black light flashlight will give the creatures away.  But don’t just squash them.  They have a job to do.  They feed on many insect pests and keep nature in balance.  Catch them with a plastic cup, slide an index card underneath, and release them out of doors where they belong!