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. 

Coffee and The Brain: The Surprising Science Behind Hot, Brown, Bean-Water

Author: Ryan Wardle 

Coffee - who doesn't love starting the day with a cup of the world's the most commonly used psychoactive drug? Whether we drink it or not every one knows about the magic brown liquid that gives an extra jolt of energy. We love it so much that Americans drink over 400 million cups of the stuff every day. That pick-me-up energetic feeling is due of course to the molecule that we've all come to know and love, caffeine. 

But what even is caffeine? And how does it work? Is it healthy? Or is it harmful? We'll find out the answers in today's installment of Remarkable Physiology as we explore the fascinating effects that caffeine has on our brains and bodies. So go pour yourself a nice cup of joe and we'll get into it. 

The Brain for Beginners

The brain, a.k.a. the noggin, a.k.a the noodle, a.k.a old thinky,  is a crazy complicated and wonderful organ located inside your head. It is where thinking, feeling, and the entire internal experience takes place. It is composed of billions of cells known as neurons, forming trillions of connections with each other. Each neuron is connected to other neurons via a long structure called the axon. The neurons convey messages from cell to cell by sending electrical impulses down the axons to the receiving end of the target cell where it is received into the dendrite. It's like the internet, except inside your head.

But here's the weird part: the axon and the dendrite never touch (Think middle schoolers dancing).  There is a gap, or synapse, between the two cells. When the electrical signal reaches the end of the axon it triggers the cell to release signaling chemicals, known as neurotransmitters,  into the synapse. Neurotransmitters then bind to receptors across the synapse on the dendrite of the receiving cell. And thus the message transfer is complete and the new cell generates an electrical signal to send off to another neuron. This pattern of changing electrical to chemical, back to electrical is going on constantly inside your brain and throughout your entire nervous system.

Each neurotransmitter has a specific receptor that it binds to, sort of like a lock and key. Or perhaps a more evocative example would be those things babies use to learn shapes where each block can only fit in to it's particular hole. Yah, neurotransmitters are like a microscopic version of that. When the right shaped transmitter binds to its receptor is causes a change in the receiving neuron that generates a new electrical impulse.

Your Brain on Coffee

The neurotransmitter that's relevant to us caffeine addicts is adenosine. Adenosine is a sleepy molecule. It is released and builds up in the brain throughout the day, and as it binds to its receptors in the synapses it causes us to feel tired. But we don't have time to be tired! There's too many meetings to attend and proposals to write. And that's why God in his infinite wisdom created caffeine. Caffeine closely resembles adenosine. Basically what caffeine does is mimic adenosine, and binds to its receptors. This jams the neuron signaling, and now the message of "tired" can't be received.

How do we know this is what's happening? Crazy you asked that, because here's how!
In the graph right (Fredholm, 1980) we can see the effect of caffeine on different neurotransmitter pathways. The x-axis is showing the level of caffeine, and the y-axis is showing how much effect that level has on different targets. Focus on the A1, A2 receptors as these are the adenosine receptors. Don't worry about what the other receptors are, just know they're other pathways that do stuff in the neurons. These receptors are effected after ingesting the dose of caffeine found in a single cup of coffee. The other pathways only become activated well after the dosage of caffeine becomes toxic - 20-40x higher than one cup! I know some coffee addicts, but even they can't drink 20-40 cups of coffee in one sitting. Also, in case you were wondering the lethal dose of caffeine is, it is estimated at 10g, or about 100 strong coffees (Ritchie, 1975).

From this experiment we can conclude that it is in fact the blockage of adenosine receptors by caffeine that is producing that energized feeling. But that feeling is a lie!

Caffeine isn't actually giving you any more energy, it's just preventing you from feeling how tired you actually are. It's sort of like if you leave the house wearing a terrible outfit, but your friend somehow convinces everyone to not make fun of you. You don't actually look good, you're just not hearing how bad you do look. And all that adenosine keeps building up in the synapses, so after the caffeine molecules are degraded and the stimulating effect wears off the receptors become flooded with adenosine and you "crash". That's why you may feel even more sluggish and tired than before. In this way caffeine is sort of like a credit card where you feel like you can spend the energy now, only to later find out you didn't have any to begin with. So the perceived effect of energy can be helpful, but it comes at a cost. Caffeine goes beyond stimulation however and has many other effects on the mind and body.

Can Coffee Prevent Alzheimers and Dementia?

If you didn't already think caffeine was a wonder drug you will now. It turns out that drinking coffee might be a great way to prevent the onset of dementia or Alzheimer's disease later in life. Eskelinen et al., (2009) found that moderate coffee consumption in mid-life could reduce the likelihood of dementia and Alzheimer's later in life by up to 70%. A long-term group study of 1409 participants found that those who drank 3-5 cups of coffee per day in middle-age had a 65-70% decreased risk of dementia and 62-64% decreased risk of Alzheimer's disease when followed up with 21 years later.

The proposed mechanisms for this effect include coffee decreasing the risk of type 2 diabetes, which is associated with dementia. Another idea is that the caffeine and adenosine A2a receptor molecules prevent cognitive deficits related to the Alzheimer's associated protein amyloid-beta. Also it may be due to the antioxidants found in coffee. But no one really knows!

This same protection did not hold true for tea. I like tea, but you know how we all have that one friend who only drinks tea and is always going off about how much better it is than coffee and why tea is so great, and yada yada yada? Well next time they go off, just show them this. That oughta shut them up.

So in addition to helping you feel awake and tasting delicious it turns out coffee might help prevent degenerative neurologic diseases as well. Remarkable!

The Dark Side of the Dark Roast: Negative Effects

Surely coffee can't be all warm cozy mugs of delicious, energizing, dementia-fighting roast nut water though, can it? There has to be some downsides. The two most commonly cited negative effects of coffee are anxiety and insomnia. When looking at anxiety there was no significant effect of caffeine consumption on anxiety in the US (Eaton and McLeod, 1984) or UK (Warburton and Thompson, 1994). This may not be telling the whole picture however, as people who are prone to anxiety often avoid caffeine. The same general trend is true for insomnia where there is no effect of caffeine intake on insomnia, yet likely due to the fact that people who suffer insomnia avoid caffeine.

Another concern people have is that caffeine raises blood pressure. This is true, but maybe not in a relevant way. It is raised by a very small amount that some doctors believe to be harmful, and others believe to be fine. Additionally, caffeine is feared to raise blood cholesterol. This effect is eliminated when using filtered, percolated, or instant coffee, and is only an issue with boiled or turkish coffee.

So really then are the downsides that bad? I was lead to believe by public opinion that coffee had serious negative health consequences. But now I'm not so sure, the science seems less condemning. I wouldn't be surprised to learn there are some minor consequences, but I am definitely surprised to learn about the potential benefits of fighting dementia and Alzheimer's. If nothing else I don't feel so bad when drinking coffee now. Thank you science for always being an enabler for our addictions!

Conclusions

To wrap this all up, caffeine is a pretty cool chemical with a fascinating method for disrupting neuron activity to make us feel energized. It also may have the power to protect our neurons and minds from debilitating diseases when consumed as coffee. And even the negatives don't sound so bad. I think this chemical is so wonderful that we should stop calling it caffeine and start calling it caffriend.

References

Eaton WW, McLeod J (1984) Consumption of coffee or tea and symptoms of anxiety. Am J Public         Health74:66–68

Eskelinen, M. H., Ngandu, T., Tuomilehto, J., Soininen, H., Kivipelto, M. (2009) Midlife Coffee and     Tea Drinking and the Risk of Late-Life Dementia: A Population-Based CAIDE StudyJournal of           Alzheimer's Disease 16: 85-91

Fredholm, BB (1980) Are methylxanthine effects due to antagonism of endogenous adenosine?           Trends Pharmacol Sci 1:129–132

Goodman LS, Gilman, A Ritchie JM (1975) The xanthines. in The Pharmacological Basis of           Therapeutics, (MacMillan, New York), pp 367–376.

Warburton DM, Thompson DH (1994) An evaluation of caffeine in terms of anxiety, depression and     headache in the general population. Pharmacopsychoecologia 7:55–62.