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The Ugly, the Uglier and the Ugliest

Desert Food Chain - Part 13

Of all the creatures that haunt your bad dreams, especially if you live in our Southwestern deserts, the millipedes, centipedes, scorpions and spiders, whether venomous or not, probably rank near the top of the list. 

Even though all have limited mobility and range, the millipedes, centipedes, scorpions and spiders – like their arthropod kin, the insects – occupy widely diversified environments almost across the globe. 

Like the insects, too, they all have jointed external skeletons.  “Components of the skeleton meet (articulate) at joints, which allows one part of the body to move in relation to another,” says Barbara Terkanian in her article “A Vertebrate Looks at Arthropods,” which appears in A Natural History of the Sonoran Desert.  “Muscles spanning joints and anchored to different parts of the skeleton provide the power for movement.” 

The millipedes, centipedes, scorpions and spiders, however, do have distinguishing characteristics, and each of the creatures plays a distinctive role in the desert food chain.

The Millipede

A millipede, shaped much like your little finger, has a multi-segmented body, with two pairs of legs on each segment (hence the name “millipede” or “thousand feet”).  It grows and sheds throughout its lifetime, adding a new segment and legs with each shed.  Typically, the millipede ranges from tan to reddish brown to black in color.  “The body structure of most millipedes,” according to the National Park Service’s Petroglyph National Monument Internet site, “includes a calcified head for digging in soil, antenna for sensing things like food, ocelli (simple eyes) for sensing light, mandibles for chewing food, a telson for waste excretion, and secretory glands for self defense.” 

The millipede’s ancestors marched near the head of the parade of the earliest animals to emerge from the sea and walk on dry soil.  Some early millipedes, among the largest dry-land invertebrates in the fossil record, measured more than six feet in length and nearly two feet in width.  Today, most species of desert millipedes measure only a few inches in length and less than half an inch in width. 

The millipede takes refuge from the desert heat and drought in an underground burrow, sometimes appropriating an ant burrow, according to Floyd Werner and Carl Olson, Insects of the Southwest.  It emerges to feed in the coolness of night or to celebrate in the desert’s rejuvenation after a rainfall.  It counts on the soil moisture within its burrow and the waxy coatings on its body to conserve water.  According to Renée Lizotte’s article in A Natural History of the Sonoran Desert, the millipede mother lays her eggs in concealed places, then abandons them, trusting that her offspring will be able to shift for themselves.  Those that survive can live for 10 years or more.

While a millipedes does not bite or sting, it does wind itself into a spiral shape when threatened, and it exudes a foul-smelling and evil-tasting toxic brown liquid from glands near the tops of its legs.  The liquid can trigger a mild to severe allergic reaction in some people.  Even if you are so inclined, it is best not to go around handling or eating millipedes. 

In its place in the desert food chain, the millipede – one of nature’s recyclers – feeds on just about anything that has died, according to NPS’s Petroglyph National Monument Internet site.  In the desert, where the dry climate tends to preserve organic matter, the millipede accelerates the process of decomposition, reintroducing nutrients to other organisms.  Slow-moving creatures, the millipede has great patience and persistence.  For instance, generations of millipedes may feed for many decades on the trunk of a fallen tree. 

The millipede’s only real enemy, say Werner and Olson, is “the larva of a beetle called Zarrhipis.  This is a slender yellow-and-black-banded larva up to two inches long, with a vicious bite and obvious venom.  It searches down millipedes, kills them with a bite and eats its way down inside from the front.”

The Centipede

While they may look somewhat similar, the centipede differs markedly from the millipede.  It has a rather flattened, rather than a cylindrical, multi-segmented body trunk, with a single pair, instead of two pairs, of legs on each segment (hence the name “centipede,” or “hundred feet”).  The six- to eight-inch-long Giant Desert Centipede, the most conspicuous of our various desert species and one of the largest in the world, typically has an reddish-yellow body with a darker head and tail – a visual signal to the world that it can deliver a venomous bite.  Its head comes equipped with sensing antenna, and, according to the Backyard Gardener Internet site, “On the first segment behind the head, the centipede has hollow tubes [actually modified legs near the mouth], with openings at their sharpened tips that function as fangs. 

They are attached to venom glands, and are used to kill prey.”  As the Pestcontrol Internet site says, at its tail, the Giant Desert Centipede possesses a “‘psuedohead,’ or false head, to confuse potential predators.  Thus, if a predator unwittingly grabs the psuedohead, the envenomated true head is free to bite.  The psuedohead bears elongated appendages very similar to the appendages on the head, rendering the centipede very symmetrical in nature.”  The centipede’s evolutionary predecessors, like those of the millipede, appear in fossil records hundreds of millions of years old.

Lacking the millipede’s waxy body armor, which would help protect it from desiccation, the centipede simply avoids desert heat and drought.  It seeks out the cooler and moister sanctuary afforded by burrows, caves and ground cover during the hours of daylight.  It hunts in the coolness of the night.  Like the millipede mother, the centipede mother lays her eggs in concealed places, but unlike the millipede mother, the centipede mother stays to tend her brood.  She coils protectively around her eggs and her newly hatched young for days, grooming them, presumably to ward off bacteria and mold.  The centipede may live for years.   

A ferocious and nimble carnivore, the centipede feeds on essentially any small creature it can catch, according to Lizotte.  Prey includes “mostly insects, but occasionally other arthropods [for instance, scorpions], lizards, and even small rodents.”  As naturalist Susan Tweit says in an article “Centipede – Many Legs,” SouthernNewMexico Internet site, “Despite poor vision, centipedes are hunters. They find their prey with keen senses of smell and touch, and then run towards it, propelled swiftly on gracefully flowing multiple legs. They administer the coup de grace by clasping the prey with a pair of sickle-shaped, venom-dispensing pincers at the end of their first pair of legs.”  The centipede, according to some reports, even preys on bats in some parts of the world.  Conversely, the centipede itself may fall prey to the American Pallid Bat (sometimes called “Rambo Bat”) as well as various owl species and the roadrunner. 

The centipede, according to some authorities, has a bite about equivalent to a bee sting in seriousness.  It can inflict pain, swelling, headaches, palpitations and nausea.  Its bite can, however, produce a far more serious situation.  In an incident reported by Tucson doctors Joy L. Logan and David A. Ogden in the April 1985 issue of “The Western Journal of Medicine,” a woman whose medical history “included asthma and an allergy to bee stings” suffered life-threatening disintegration of muscles associated with urination and failure of her kidneys following the bite of the Giant Desert Centipede.

Even if you are so inclined, it is best not to go around handling or eating centipedes. 

The Scorpion

The scorpion, a symbol of our Southwestern deserts, has an almost mystical hold on our collective psyche.  The mythological Scorpion slew Orion, the mighty warrior who set out to exterminate all the animals on earth.  He gave his name to one of the great constellations.  According to astrologers, he shapes the personalities of those born under his sign, making them strong-willed, egotistical, brooding, passionate, loyal and incisive. 

An actual scorpion, the wellspring of myths,  senses and captures prey with specially adapted clipper-like pincers, kills it with its stinger, and rips it apart with its mouth.  It embraces a potential mate with its pincers while the two engage in an elaborate courtship dance, with the union producing offspring that may live for years, possibly up to two and a half decades.  The mother carries her several dozen progeny on her back.  One species, the Bark Scorpion, in a behavior extraordinary for ferocious predators, gathers for large conventions, especially during the winter.  The scorpion fluoresces a brilliant yellowish-green under ultraviolet light. 

 As Steven J. Prchal says in A Natural History of the Sonoran Desert, “The long, segmented body of the scorpion is divided into two obvious sections: the elliptically shaped body and the trade-mark ‘tail.’”  Its head, which fuses with the thorax, “contains all of the sensory, locomotion, and feeding appendages…”  The head and thorax are covered by a carapace, or a shield, and a “pair of median eyes atop the carapace, as well as several lateral eyes arranged into two groups along its front edge, give the animal its limited vision.”  The body, with seven segments, has comb-shaped organs used for sensing and openings used for breathing and breeding.   The scorpion’s four pairs of jointed legs have sensory hairs that signal the presence of potential prey a foot away.  The tail is “actually an extension of the abdomen.  It consists of five segments, each one longer than the last; at the tip is the telson (stinger), which is not considered a true segment.”  Like the millipede and the centipede, the scorpion’s ancestors, with a clear family resemblance, emerged from the sea hundreds of millions of years ago.  In fact, says Dawn H. Gouge and her associates in an article “Scorpions” on University of Arizona’s College of Agriculture & Life Sciences Internet site, “Fossil scorpions found in Paleozoic strata 430 million years old appear very similar to present day species.”  Some of the early scorpions were as large as wolves.

“Scorpions,” say Gouge and her associates, “have many adaptations for desert living.  They have extra layers of lipids (fats ) on their exoskeleton (external skeleton) that minimizes water loss.  Most are active at night, and spend their days where it is cool and moist under rocks, wood, tree bark or in burrows…”  While they do drink, they “derive most of their water from their food…”

The scorpion preys, usually by ambush, on an array of creatures, including the ferocious centipedes, the insects, various spiders and even other scorpions.  The larger species may prey on small vertebrates, including both reptiles and mammals.  Conversely, the scorpion serves as a delectable tidbit for the ferocious centipede, the tarantulas, insectivorous reptiles, several birds and various small mammals, including Rambo Bat. 

Probably the most venomous of the various species in the desert Southwest is the Bark Scorpion, which produces a sting that can result in “severe pain (but rarely swelling) at the site of the sting, numbness, frothing at the mouth, difficulties in breathing (including respiratory paralysis), muscle twitching, and convulsions,” according to Gouge and associates.  

The Giant Hairy Scorpion, says Prchal, is one of the least common of those of our desert species, but it is “the largest scorpion in the United states (up to 6 inches…long).”  Fortunately, it delivers a less venomous sting that that of the Bark Scorpion. 

Even if you are so inclined, I would not recommend that you handle or eat scorpions.  I would not want to froth at the mouth. 


The spider, an evolutionary cousin to the scorpion, ranks as a star in horror movies.  In Kingdom of the Spiders, for instance, migrating swarms of tarantulas kill animals, invade a community, and besiege hotel guests.  In Arachnophobia, an introduced Amazonian spider attacks residents in a small town.  In Tarantula, giant spiders assail humans.  In the spoof Eight Legged Freaks, spiders infect film aficionados with fun-filled fright.  “Spiders always stop a show,” said reviewer Richard von Busack,  “They’re cheap to hire, and if they step out of line, you can step on them back.  They have no pressure group, and will not complain if they are misrepresented onscreen.”

“Spiders are soft-bodied arachnids with two body parts: the fused head and thorax and the abdomen ,” Renée Lizotte said in her article “Spiders,” in A Natural History of the Sonoran Desert.  A spider’s mouth comes equipped with fangs and glands which the creature uses as syringes for injecting a paralyzing venom into prey.  It has appendages, located just behind the mouth, that it uses like hands for repositioning immobilized prey.  Its venom liquefies the prey, which allows the toothless spider to suck its meal into its stomach.  Typically, the spider has eight “simple” eyes, although some have only six and some (cave-dwellers) have none at all.  Its legs, according to Lizotte, have special hairs “through which [a spider can] feel, taste and hear.”  It can sense the location of the prey “by the displacement of air around these hairs.”  The spider’s abdomen, which contains the internal organs, is equipped with perhaps its most distinguishing feature, spinnerets, which it uses to produce silk threads. 

The spider’s silk threads, finer by far than a human hair, would exceed the strength of comparable threads of steel.  It uses the silk strands for such things as weaving and anchoring its webs or nests, netting and enshrouding its prey, and swaddling its eggs.  It even weaves sail-like structures that serve to disperse the spider’s young into new areas.  Flying spiders!  The title for another horror movie? 

Like the millipedes, centipedes and scorpions, spiders appeared early in the fossil record.  “The oldest confirmed spider fossil,” according to John Pickrell, National Geographic News, August 7, 2003, “was found embedded in ancient rock deposits dating to the mid-Devonian period 380 million years ago, long before the appearance of four-footed vertebrates.”  Remarkably, a fossilized spider web “was found in Jezzine, Lebanon, by German fossil hunter Dieter Schlee in 1969 in amber beds that date to between 127 and 132 million years ago.”

Like its evolutionary kin, our desert spider copes with the desert environment by seeking daytime shelter in a burrow or other cooler location.  It hunts at night.  It sips water from moist soil and takes liquid from prey.  Some species, for instance the tarantulas, may live for two decades or more.

Spiders, an important link in the desert food chain, prey on insects and other spiders.  The tarantula, the largest spider in our deserts, may even feed on small reptiles.  Spiders become the prey of numerous animals, for instance, insects, reptiles, amphibians, birds and various mammals.  The tarantula, in a nightmare scenario, may fall victim to the Tarantula Hawk, a wasp that will “first sting the spider, paralyzing it, then lay an egg on it before burying it. The wasp larva feeds on the paralyzed tarantula which may remain alive for several months while being consumed,” according to R. L. Smith, Venomous Animals of Arizona.

While nearly all the spiders of our deserts are venomous, the infamous Black Widows and the Brown Recluses rank as the most dangerous.  The Black Widows, shiny black with a red hourglass-shaped design under the abdomen, delivers a bite that can produce aching throughout the body, severe pain in the muscles, shortness of breath, and rigidity of the legs and abdomen, according to the report IPM for Schools.  The Brown Recluse, light tan and long-legged with a violin-shaped design on its back, delivers a bite that develops into an ulcerous lesion. 

Tarantulas, hairy and fearsome looking “gentle giants,” according to Smith, will bite if handled carelessly, producing a painful, although not particularly dangerous, wound.  Its barbed and venom-tipped hairs, however, can cause severe itching and lesions where they touch human skin.  If inhaled, they can cause acute respiratory problems.  If they contact the mucous membranes of the nose, mouth or eyes, they will inflict acute inflammation and intense discomfort. 

Spider bites and tarantula hairs should probably propel you to your physician for treatment.  Even if you are so inclined, it is just better not to go around handling or eating just any old spider. 

By Jay W. Sharp


Part 1 Desert Food chain - Introduction
Part 2 Desert Food chain - The Producers
Part 3 Desert Food chain - The Cacti: A Thorny Feast 
Part 4 Desert Food chain - The Yuccas
Part 5 Desert Food chain - The Agave
Part 6 Desert Food chain - Desert Grasslands
Part 7 Desert Food chain - Desert Shrubs
Part 8 Desert Food chain - The annual forbs
Part 9 Desert Food chain - Mavericks of the Desert Plant
Part 10 Desert Food chain - Outlaw desert plants
Part 11 Desert Food chain - Animals: The Consumers
Part 12 Desest Food chain - The Insects
Part 13 Desest Food chain - The Ugly, the Uglier and the Ugliest

Also see: The Desert Food Chain for the young student



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