Desert Demon, the Solifuge

You can often tell what opinion the human race has of another animal by the number of aliases we assign to it. Just like the law-abiding citizens of the Old West, we tend to give nicknames to creatures we consider unsavory or downright mean. Such is the case with the arachnids of the order Solifugae. Depending on your geographic location, you may be familiar with them as “camel spiders,” “sun spiders,” “wind scorpions,” or “solpugids.” Not that their reputation is entirely undeserved, but these are fascinating and enigmatic invertebrates.

Two things are immediately apparent about a solifuge that are cause for alarm. The first is the animal’s sheer speed. They don’t get the name “wind-scorpion” for nothing, as they do “run like the wind,” and on only six of their eight legs. They are more agile than an NFL halfback, too. Attempts to capture them can leave you face down in the sand while at the same instant the solifuge is crossing the county line. I recall chasing a small one around the floor of an outdoor dining hall at a camp in eastern Oregon to the point of dizziness (me; the solifuge was fine).

The second thing about a solifuge you notice is the size of its jaws. Known to scientists as “chelicerae,” this pair of mouthparts can take up nearly one-third the body length of some species. They easily have the largest jaws for their size of any terrestrial animal (invertebrate at least). Each chelicera consists of a fixed upper portion and an articulated bottom joint combining to form the equivalent of a nutcracker or pair of pliers. Armed with teeth and filled with muscle, they are formidable weapons. These are non-venomous animals, but they do so much mechanical damage to their prey so quickly that they don’t need venom.

There are roughly one thousand species of Solifugae known globally, in 140 genera, and twelve families. Only two families (Eremobatidae and Ammotrechidae) occur in North America. There are about 100 species in the southwest U.S., half the North American total. The order reaches its zenith of diversity in the Middle East.

The source of much recent misinformation about “camel spiders” has come chiefly from United States servicemen and women stationed in the Persian Gulf, during both the first Gulf War in 1991 and the present conflict. Camel spiders are abundant, conspicuous arthropods there, but contrary to popular reports the animals do not reach the size of dinner plates (North American solpugids rarely exceed one inch in body length), they don’t literally run screaming across the dunes at 25 mph (they make no noise, and can only sprint at about 53 cm/second for short bursts), and they certainly don’t eat the stomachs of camels or the faces of sleeping soldiers. A widely-circulated image of a pair of camel spiders and a thorough de-bunking of the commentary that accompanies it can be found at Snopes.com.

Reality is usually far more interesting when it comes to arthropods, and camel spiders are no exception. They are highly adapted to the arid environments they thrive in. They are covered in fine hairs that help insulate them from the desert heat, with sparse, longer setae that act as sensors which help find prey by touch. There are also rows of sensory organs on the underside of the hind legs. These stubby, hammer-shaped appendages are called “racket organs” or “malleoli.” They are basically chemoreceptors, literally sniffing out information about the substrate the animal is traversing. Solpugids can even detect subterranean prey at a shallow depth, through the malleoli and tapping movements of the pedipalps.

The pedipalps, which in solpugids are easily mistaken for the first pair of legs, are long, stout, and tipped with “suctorial” organs that are useful to the animal when it needs to ascend vertical surfaces, or pin down struggling prey.

The first pair of legs, immediately behind the pedipalps, are very slender, and also used as sensors, waving constantly along with the pedipalps. A cornered camel spider may rear up, waving both pairs of appendages menacingly, and opening its jaws.

Given their overall aggressive nature, one wonders how camel spiders are able to reproduce without killing each other first. Indeed, the “attack phase” during courtship can easily be mistaken for an attempt at cannibalism by a male intent on mating. The female repels his advances, flees, or assumes a submissive posture. The male then grasps her mid-body and massages her with his jaws while stroking her with his pedipalps and first pair of legs. He may lift and carry her a short distance, or simply continue courting at the initial spot of contact. He eventually secretes a droplet of sperm from his genital opening, cradles it in his jaws, and uses his chelicerae to force the sperm into the female’s genital opening. Mating rituals vary among the different families of camel spiders, but the basics are consistent.

Look for camel spiders mostly at night. Some are active by day (hence “sun spider” as an alternative name), but most North American species are nocturnal. They can be seen around outdoor lights where they prey greedily on insects that have fallen to the ground. By day, flip over boards, flat stones, and cow patties, as solpugids often seek refuge under such debris. Be sure to return the object to its original position to afford shelter to other organisms. Some species actively excavate burrows where they weather the daytime heat.

Search for virtual solpugids online at informative websites like The Arachnid Order Solifugae, and Solpugid Productions. The Biology of Camel-Spiders, by Fred Punzo (Kluwer Academic Publishers, 1998) is the best book reference to date.

Given their frenetic lifestyle, solpugids are not recommended as pets. They need their entire adult lifespan to find mates and reproduce. Enjoy them where you find them; and be glad you aren’t a prey-size animal yourself.