Camel Spiders - Wind Scorpions
Text and Photographs by Eric R. Eaton
Few desert animals are as perplexing or alien-looking as the solifuge. Just like the terrifying human outlaws of the Old West, the arachnids of the order Solifugae go by many an alias: “camel spider,” “sun spider,” “wind scorpion,” and “solpugid” among them. They have a reputation exaggerated by myth, superstition, and urban legend, but in reality are fascinating and enigmatic animals. Intimidating as they may be in appearance and behavior, they are, thankfully, basically harmless to people and pets.
Two things are immediately apparent about a solifuge. The first is their sheer speed. They don’t get the name “wind-scorpion” for nothing. They do run like the wind, and on only six of their eight legs at that. They are more agile than an NFL halfback, too. They accomplish all this on usually rugged terrain or soft sand that leaves most other animals hobbling or sinking. Solpugids are also surprisingly good climbers.
Should a solifuge ever stop moving, the second thing you notice is the size of its jaws. These “chelicerae,” as scientists call them, can take up nearly one-third the body length of some species. They have the largest jaws for their size of any terrestrial invertebrate. Each chelicera consists of a fixed upper portion and an articulated bottom joint forming the equivalent of a nutcracker or pair of pliers. Armed with teeth and filled with muscle, they are formidable weapons. Each one moves independently, allowing the solifuge to rip and tear its prey. These are non-venomous animals, but they do so much mechanical damage to their victims, and so quickly, that they don’t need venom.
Diversity and Distribution
There are roughly one hundred species of Solifugae in the southwest U.S., half the North American total. Only two families (Eremobatidae and Ammotrechidae) occur in North America. At least three species make it into southern Canada, in southeast British Columbia, southern Alberta, and extreme southern Saskatchewan. The order reaches its zenith of diversity in the Middle East. Associating the sexes remains a major obstacle to identifying them. Many species are currently known from only a single male or female specimen.
The source of most recent falsehoods about “camel spiders” has come 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 are voiceless, and can only sprint at about 53 centimeters per second for short bursts), and they certainly don’t eat the stomachs of camels or the faces of sleeping soldiers. Camel spiders cannot jump, either. A widely-circulated image of a pair of camel spiders strung together purported to show a single, multi-legged animal; and the forced perspective greatly exaggerated the size of the arachnids.
Anatomy and Lifestyle
Reality is far more interesting when it comes to camel spiders. They are highly adapted to the arid environments they thrive in. Covered in fine hairs, they are insulated from the desert heat; sparse, longer setae 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.
Solpugids are covered in bristles and fine setae (hairs), some of which are very long, and keenly sensitive to air currents and other tactile stimulation. Denser coatings of hair help insulate the creatures against the extreme heat of the desert environment.
Reproduction and Development
Given their overall aggressive nature, one wonders how camel spiders reproduce without killing each other first. Indeed, the “attack phase” during courtship can 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 these basics are consistent.
What little we know about the growth and lifespan of solpugids is cobbled together from studies of a wide range of species, most of which do not occur in North America. Captive specimens may not always be representative of wild individuals, either. At least two members of the family Eremobatidae were shown to lay eggs, deposited by the female in her burrow. Female Eremobates durangonus laid batches of 20-264 eggs under laboratory conditions, about eleven days after mating. The young that hatch go through eight instars before reaching sexual maturity as adults. An instar is the interval between molts. Like all arthropods, solpugids must periodically shed their exoskeleton in order to grow. Solpugids probably "live fast and die young," with the average lifespan hardly exceeding one year.
Most North American camel spiders are nocturnal, though some are active by day (hence “sun spider” as an alternative name). They can be seen around outdoor lights at night where they prey greedily on insects that have fallen to the ground. By day, they hide under boards, flat stones, cow patties, and other objects. Some species actively excavate burrows where they weather the daytime heat.
Solpugids seem to behave much like shrews, frantically searching for any animal their own size or smaller to kill and consume. Most other arachnids, insects, and other invertebrates are on the menu, though termites may make up the bulk of their diet, especially in the case of young solpugids. Adults may occasionally scavenge larger animals like small lizards and snakes, that are road-killed or the victims of larger predators.
Solpugids and You
Their nomadic lifestyle occasionally leads solpugids into homes, cabins, buildings, and other human dwellings and businesses. There is no cause for alarm, but you may wish to usher the arachnid into a container and take it back outdoors. Meanwhile, prevent the entry of all kinds of unwelcome arachnids and insects by repairing worn weatherstripping on the bottom of doors, mending holes in window screens, and sealing cracks and crevices. Carefully inspect objects you bring indoors from outside. This includes firewood, children's toys, and garden equipment.
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-sized animal yourself.
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