Sunday, August 15, 2010

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.

33 comments:

  1. Quite a fine piece of nature writing Eric. Guess I won't find any of these around here, but I got a pretty good picture just reading this...and seeing your shots.

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  2. Thanks for showing and explaning the malleoli. I have seen a few solpugids in the desert, but never belly-up. Very interesting!

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  3. Very interesting post! Love the belly up photo, how intriguing.

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  4. Freaky looking animals- it took a couple of years living out west to get used to solpugids. Now that I'm in the midwest I miss having them around.

    Great article, Eric.

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  5. We do have them as pets now - at least there seems to be a whole litter of half grown ones in the house. Maybe the offspring of the one in your top photo. I hope they and the little house geckos like sharing all those moths and male velvet ants that seem to find their way to any lighted room. And no - we don't live in a tent...

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  6. I used to keep them as pets when I lived in California - I had plenty of prey to keep them happy from the insectary I worked in. They are FUN to feed! Vicious attackers would be an understatement.

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  7. Thank you for this post. After spending the day in the west desert of Utah, we found one of these ugly guys wandering around our bedroom after we returned home. Was wondering if it hitched a ride on someone's clothes or something. Creepy!

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  8. We found a small one in our home. Are they dangerous? I am freaked out. We live in Riverside, CA

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    1. No, they are not the least bit dangerous to people or pets.

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  9. They do attack people tho I got bite by one in Kenilworth Utah Wednesday

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    1. No, they do NOT attack people. If you got bit it had to be because you were handling the animal.

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  10. Thank you! your last picture is the type I just encountered. not a clue what it was. I made everyone move inside fast. Wish I could have gotten you a new picture but my camera inconveniently died on me. this guy had me worried mostly because of it being the size of my hand. thank you again. just glad to know it won't harm me or my doggies. pretty wicked and neat looking creature they are!!

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    1. Thank you for sharing your story, Cammie! Glad I could help put your mind at ease.

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  11. Thank you for this blog! We are from NC and the Army thought it would be cool to send us to El Paso, TX for our first duty station. I found one of these in my kitchen this morning before the kids woke up. I have kept it in a jar trying to find out if it is harmless enough to let go outside. Those jaws look killer! I think I will let it go across the road somewhere now that I have read this. :-)

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    1. So good to hear your story! I do hope your time in El Paso will include more happy surprises than scary ones. Thanks for being kind to arachnids :-)

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  12. Very interesting spider, flying scorpion fits it perfect. I'm sitting in my garage in central Texas and noticed what looked to be a half breed zipping across the driveway. Are they topically found in Texas?

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  13. Wow what a remarkable species!
    I found one here in central Texas and it's the first time I ever seen one and I have thirty five years here in the lone star state!... Pretty cool to be able to enjoy a new insect I was getting Board of the thousands of topical spiders we have here. Thank you for the info.
    Matt I

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  14. Fountain hills Arizona, this came walking out of my closet, do not know how it got there? On me? My dog ? Who has very long hair? Gross I'm totally freaked out, the bug man came today!,

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  15. I stepped on one last night ,,,yes I was barefoot,,,it was dark in the kitchen,,,after screaming like a loon,,telling my brother I would surely die!,,,he calmly scooped up the still alive little beastie,, looked him up,, and found your very informative pictures and meaning,,,thank you,,I'll be wearing shoes from now on,,,,,,from coachella valley,,I thank you!

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    1. You are very welcome! Glad no harm came to either party :-)

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  16. I just caught one of these under the blankets on my bed I'm in NE Oregon

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  17. Replies
    1. Any animal smaller than they are is fair game, including small lizards.

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  18. Do these guys live in West Africa, too? I was there last year and I swear this is the same fast-running dude that gave me quite the scare.

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    1. Hi, Kellie. Yes, they do indeed live in most all arid habitats around the world.

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  19. Thanks for the post. I saw one of these for the first time in a parking lot in Arizona recently. I'd never seen something with "10" legs before. So I was stumped. I'll never cease to be amazed at what nature has come up with. Here is a link to a picture I took. It was a feat to catch up to the thing - I actually had to follow it in my car through the parking lot - it moved so fast. Marvelous.
    https://drive.google.com/file/d/15XoIp4iObpFELrE5T6J5RpFNKcDgV7_ePQ/view?usp=sharing

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  20. Camel spiders are found in many parts of world and their is huge misconception that they are found only in iraq.

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  21. I encountered my first solpugid yesterday on a farm near Hermanus, Western Cape. Boy do they move at a startling speed. Tried to photograph it but couldn't keep up with it. Pleased to have had a chance to encounter one but can see why it would creep some people out. Thought it was an Antlion at first but finding your site confirmed exactly what to now look out for.

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  22. I have found them - rather small ones- less than an inch long in Billings Montana near the airport.
    It has been said that they fall from planes when they drop their landing gear. The planes are Canadian, near the peat bogs.
    I doubt they make it thru the winter here as they were spotted in a garage about two miles from the runway.

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    1. Those are most definitely *native* species; and they can easily survive winters there by burrowing underground.

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