Scorpions of the Chihuahuan Desert

Roll over any random rock of fair size in the American southwest and before long you’re bound to come face to face with one of nature’s most efficient, feared, loathed, and misunderstood creatures.  Though of comparatively diminutive size and reclusive habit, the scorpion has long been a symbol of the southwest, of danger and formidability.  Armed with an ironclad exoskeleton, a pair of scissor-like pincers and a long, segmented tail that ends in a sharp, curved meathook-like sting capable of delivering a powerful dose of venom to predator and prey alike, it is no wonder man has long held the lowly scorpion with a mixture of distanced respect and general disdain.  Often seen as vermin or at best an outdoor hazard to be constantly on the alert for whenever hiking, camping, or just walking around barefoot at night, residents of the southwestern United States learn quickly not to tread on them, and individuals once stung are usually twice shy.  Shoes are shaken out with force, bedsheets checked thoroughly before turning in for the night.  As my wife’s grandfather once commented, “If you ever feel strong just try to hold down a scorpion with your thumb.”

As an inquisitive child growing up in the western cross timbers, I quickly became acquainted with the local flavor of scorpion, Centruroides vittatus, better known as the striped bark scorpion.  In fact, one of my earliest memories was that of a neighborhood friend and I discovering one in my back yard.  I mentioned this to my mother years later and she told me I must have a very good memory, as we moved from that house before I turned five.  (I prefer to think of my memory bank as being more selective than vivid.)

IMG_0015.jpg

Striped bark scorpion

As fate would have it, our move deposited us on the edge of the Wilson Prairie in western Wise county, which to a budding young naturalist served as a personal classroom.  And it was a hard lesson learned the day I rolled over a log and unknowingly placed my hand on a bark scorpion taking a siesta on the other side.  One moment I was struggling to free the log from its place in the ground and the next I was howling in pain as my thumb was set ablaze by some new invisible form of fire.

Several years (and several more stings) later, I began to make summer pilgrimages to the Chihuahuan desert.  By this time my love of all things venomous  had expanded to include spiders, centipedes, and snakes.  It was there that I was introduced to an entirely new and different crop of scorpions, and my knowledge and appreciation of these fascinating arachnids began to evolve.  The now-familiar bark scorpion, inarguably the most common species in the state, was still present, although these desert variants were marked somewhat lighter.  A friend and I found several examples of these in the creek drainage between Terlingua and Lajitas while hunting lizards among the catclaw (a much more dangerous activity).  Centruroides vittatus is very fond of wooded areas, where it finds suitable shelter in piles of dead fall as well as behind the loose bark of old oak trees, hence the common name.  But here in the desert, oak trees are a rare sight indeed, and so this species (as well as most of the others that call this arid environ home) utilizes the cool, moisture-retentive spaces beneath and between rocks.

The next genus I came across in my adventures to the Big Bend area were the Diplocentrus scorpions.  Larger, darker, with thick pincers and a more irascible disposition, these shiny black arthropods were common beneath rocks in the Christmas Mountains in southern Brewster county.  Before long I identified them as Diplocentrus lindo.  Although their stings are very mild, they make up for this with a strong pinch not unlike that of a small crab.

d-lindo

Diplocentrus lindo

I’ll never forget my first Diplocentrus whitei.  While shining rock cuts for snakes on highway 118 between Terlingua and Alpine my beam fell upon an enormous shiny black scorpion protruding from a dime size hole that had been excavated from the side of the cut.  Only its pincers were exposed, but they were immense!  The creature immediately scuttled back into its subterranean shelter, hiding from this foreign intrusive artificial light that had so suddenly and rudely interrupted its night.  Dismayed at not being able to extract and observe such an uncommonly large and impressive scorpion as this one, and yet not willing to destroy its home and habitat just to get a peek at it, I devoted the remainder of the night to finding one out in the open.  Several cuts later and I got my chance.  This one had no place to hide, but it did have a plan B, which it executed with all the vigor and vim of a cornered mountain lion.  The oversized pincers raised, clicking together audibly as it snipped at the air.  The arched tail followed between snips, thrusting forward, seeking flesh.  I had to admire its insane courage, and was grateful for the fact that I was much larger than it.  After a snapshot or two I left it there to calm down and resume its nocturnal wanderings.  Diplocentrus whitei is unique among Texas scorpions in that it occurs north of Mexico only in the Big Bend region.  It is also the state’s largest scorpion, with adults achieving maximum lengths of well over two inches.

d-whitei

Diplocentrus whitei

Diplocentrus lindo and D. whitei are the only two members of the genus occurring north of the Rio Grande, but another group of scorpions, Vaejovis, are among the most diverse and numerous.  Generally smaller and paler, with thinner pincers, tails, and bodies, this huge genus of scorpions can be very common in the Chihuahuan desert.  In fact, my first Vaejovis waueri was found in my motel room hanging out on the floor by the lamp stand on a routine trip to the ice chest.  An olive green beauty with black pincers and dark brown stripes along the abdomen, it is one of our more colorful native scorpions.

Identifying other members of this genus to species can be tricky, as there are quite a few, including the quick and aggressive V. intermedius, the straw yellow V. crassimanus, and the ghostly pale V. russelliVaejovis coahuilae, perhaps the most common species, always turns up around the blacklight I set up to attract night flying insects at the Longhorn Ranch motel north of Study Butte, eager to take advantage of the free buffet.

Vaejovis-Paroroctonus (1).jpg

Scorpions of genera Vaejovis (top) and Paruroctonus (bottom)

A fourth genus, Paruroctonus, is the largest genus of scorpions in the U.S., although the Chihuahuan desert boasts only four species, being far outnumbered here by Vaejovis.  These typically resemble bark scorpions in appearance, although they are of more pallid coloration.  P. gracilior and P. utahensis are both typical species, and fairly common, although the genus includes such rarities as P. boquillas (named after Boquillas Canyon in Big Bend National Park, where the type specimen was found), to P. williamsi, of which few specimens are known.

The genus Pseudoroctonus includes only a single native species, and this is P. reddelli, the Texas cave scorpion.  Initially described as Vaejovis reddelli, it is a common and widespread species found only in and around caves in central and western Texas.  Specimens of this reddish brown to black hued species make their homes inside the caves, and field research has shown that those attain greater lengths than the ones living around the cave mouths.  Habitat specific, they are also highly specialized feeders, with their diets consisting almost solely of cave crickets.

Scorpions are unique and interesting members of our native fauna in the Lone Star state, and the complex details of their lives include such intriguing aspects as mating “dance” rituals, variable venom compounds, and the fact that their exoskeletons possess a combination of chemicals (including beta carboline) that cause them to glow yellow or turquoise under ultraviolet light.  Far from being hideous, revolting, deadly, or a cause for panic and alarm, they are true biological wonders that fill an important niche in our natural world.  They are important consumers of insects, miniature armored tanks well-enough adapted for survival that they were around long before the dinosaurs, survived the Ice Age, and continue to thrive in the ever-encroaching presence of man.  Their diversity and very presence help make the desert what it is, a wonderful, mysterious landscape full of life, provided one is inclined to turn the occasional stone and peer for a moment into their secret world.

Leave a Reply

Fill in your details below or click an icon to log in:

WordPress.com Logo

You are commenting using your WordPress.com account. Log Out / Change )

Twitter picture

You are commenting using your Twitter account. Log Out / Change )

Facebook photo

You are commenting using your Facebook account. Log Out / Change )

Google+ photo

You are commenting using your Google+ account. Log Out / Change )

Connecting to %s