Creepy-Cool Camel Spiders

Creepy-Cool Camel Spiders

Author: Jared E. Hollows

            As a deployed soldier, I first encountered camel spiders during my tours in the Middle East, Africa, and later in Afghanistan. I distinctly remember the first time I saw one in my tent. Startled, I jumped up on the nearest crate, horrified by the fist-sized, alien-looking creature that charged at me! More accurately, it sprinted toward me with front legs raised and a gaping maw that looked uncomfortably similar to dual crab claws. I may have thrown my boot at that camel spider, and I was the subject of everyone’s jokes for several days after. Perhaps after looking at the picture of a representative specimen, you might understand why someone might be a little freaked out.

Fun Fact: camel spiders can scurry at speeds up to 10mph (Punzo, 1998) – that’s almost half of the fastest human sprint on record!

Figure 1: Camel spider aggressive posture

            Going back to early human records, the camel spider’s fearsome appearance and behavior have led to quite a few exaggerations, sometimes elevating it to a creature of legend (Punzo, 1998). Rumors persist of a half-spider, half-scorpion that grows larger than a dog, sometimes even a man, and is capable of killing large vertebrates. Others remain convinced that camel spiders must carry a lethal venom. While both are quite far from the truth, the camel spider is a fascinating creature with unique adaptations that allow over 1,100 different species to survive in arid habitats all over the planet (Punzo, 1998).          

Figure 2: Camel spider variation - Morocco (L) & Egypt (R)

Fun Fact: the name Solifugae derives from Latin for “those that flee from the sun,” seeking to regulate their temperature by following sources of shade....like camels (Punzo, 1998).

            Known scientifically as Solifugae, the camel spiders are also commonly referred to as wind scorpions and sun spiders depending on the region (Punzo, 1998). However, these common names are not quite accurate. Solifugae are neither true spiders nor true scorpions, even though they do belong to the larger class Arachnida (Punzo, 1998). Unlike many spiders, Solifugae cannot spin silk, and lack the defined tail segment of scorpions (Punzo, 1998). Like many arthropods, camel spiders show great variation in size an appearance across its many species, ranging in size from one-half inch to around six inches long (Punzo, 1998). Found in deserts and arid regions across every continent except for Australia and Antarctica (including the U.S. Southwest), camel spiders are aggressive ambush predators that prey upon large insects, amphibians, rodents, small birds, and lizards (Punzo, 1998). Did I mention they are fast?

The Usain Bolt of Ground Arthropods

            So, what allows these camel spiders to move so much faster than other terrestrial insects? Solifugae have adapted a well-defined tracheal system to improve respiration, as opposed to the simple book lungs common to many insects, including spiders (Franz-Guess et al., 2016). The term lungs may be somewhat confusing and are unlike the muscular contractions of vertebrates that bring oxygen in, and force carbon dioxide out. Book lungs and simple trachea common in many spiders function by letting oxygen pass into the body through a small opening, where it travels through a folded airway that allows gas diffusion into nearby hemolymph (insect blood equivalent). By comparison, this system would not support the increased respiratory needs of camel spiders, required to fuel their strong musculature (Franz-Guess et al., 2016). To meet these needs, camel spiders have a highly developed tracheal system with multiple openings that connect to a highly branched airway that supplies oxygen directly to tissues that need it (Franz-Guess et al., 2016). Although this anatomy is not strictly unique to camel spiders, they expand on that design. The tracheal system of the camel spider tends to have a larger diameter than other arthropods, serving to let in more oxygen and cut down on weight in the large, muscular mouthparts (Franz-Guess et al., 2016). I tend to think of the terrestrial arthropod race as: strong musculature + reduced weight + increased gas exchange = gold medal in spider Olympics.    

Figure 3: Open respiratory slots

Figure 4: Advanced camel spider tracheal system (cyan)

Fun Fact: Why don’t arthropods grow as large as their prehistoric cousins? – there was much more oxygen in the air and water, with the potential to cause oxygen toxicity in larvae were they too small (Verberk and Bilton, 2011). 

  

Its Bite is Worse than its Bark

            Many insects rub body parts together to produce a sound (like crickets). The camel spider rubs its mouthparts (chelicerae) together to make an odd rattling noise, often used as a warning (Punzo, 1998). But it is the extremely strong bite from the camel spider, coupled with natural aggression, that gives it such a fearsome reputation. A comparative analysis has found that camel spiders display a bite force range that is very similar to the pinching force exerted by the claws of larger scorpions (Van der Meijden et al., 2012). In the absence of venom, this fairly unique adaptation allows the camel spider to quickly pulverize its prey, able to crush insects, light bones (birds), and tear into flesh (Punzo, 1998). This vicious assault is really meant to subdue its prey.  To feed, smaller chunks of tissue are masticated between the pincers and broken down with digestive enzymes, allowing ingestion of a nutrient soup through its pharynx (Punzo, 1998).     

Figure 5: Camel spider chelicerae musculature - tendon (red) & levator muscle (blue)

Sticky Fingers

            What about capturing fast-flying insects? In a desert environment where prey may be scarce, the voracious camel spider has evolved to snag flying insects (Willemart et al., 2011). Solifugae have characteristic adhesive organs located at the tips of their front legs, called pedipalps (Willemart et al., 2011). These specialized legs are not used all that much for mobility, acting as more of a sensory apparatus that is capable of strongly adhering to feathers, scales, and skin via small suction cups (Willemart et al., 2011). Unlike other insects, no adhesive secretions are used (Willemart et al., 2011).    

Figure 6: camel spider suctorial organ

Figure 7: cricket ensnared by camel spider suctorial organ

Fun Fact: the adhesive organs on the pedipalps allow the camel spider to easily climb smooth glass surfaces without missing a beat, currently modeled in novel bio-grip devices

(Willemart et al., 2011). 

Figure 8: cricket escape trajectory halted (C) by camel spider suctorial organ 

Conclusion

             Camel spiders might look like alien lifeforms, but they have adapted quite well to life on Earth. Solifugae have pincers more akin to crushing claws, suction cups that will stick to anything, and the stamina to chase down almost any prey. It is no wonder that many references describe this arachnid as truly raptorial.    

References:

Franz-Guess, S., B-J. Klubmann-Fricke, C. S. Wirkner, L. Prendini, and J. M. Starck.       2016. Morphology of the tracheal system of camel spiders (Chelicerata: Solifugae) based on micro-CT and 3D-reconstruction in exemplar species from three families. Arthropod Structure & Development 45: 440-451.

Punzo, F. 1998. The Biology of Camel-Spiders (Arachnida, Solifugae), Springer             Science+Business Media New York. Pp. 1-151.

Van der Meijden, A., F. Langer, R. Boistel, P. Vagovic, and M. Heethoff. 2012. Functional morphology and bite performance of raptorial chelicerae of camel spiders (Solifugae). The Journal of Experimental Biology 215: 3411-3418.

Verberk, W. C. E. P. and D. T. Bilton. 2011. Can oxygen set thermal limits in an insect and drive gigantism? PLoS ONE 6(7): e22610.

Willemart, R. H., R. D. Santer, A. J. Spense, and E. Hebets. 2011. A sticky situation:       Solifugids (Arachnida, Solifugae) use adhesive organs on their pedipalps for prey           capture. Journal of Ethology 29: 177-180.

Fair-use Images:

American Military News. 10 crazy pictures of camel spiders to remind you of the Middle            East. http://samericanmilitarynews.com.

Ritchfield, J. 2012. Solifugae ventral aspect of region that includes the respiratory slots            and malleoli. http://wikimediacommons.com.

Ritchfield, J. 2010. Modest-sized Solifugid near Uniondale, Western Cape, South Africa.          http://wikimediacommons.com.

Siwanowicz, I. 2015. Close up on the fearsome jaws of camel spiders. http://amnh.org.