A curious defense mechanism of some scorpions

Parabuthus transvaalicus is a mean-looking scorpion, commonly known as the Transvaal thick- or fat- tailed scorpion, dark scorpion or spitting scorpion. It lives mainly in Southern Africa. Here’s a picture sure to give you the heebie jeebies; I know it gives it to me.

scorpion
Credit: http://www.scorpion-forum.com

I am not particularly fond of these animals, but I love venoms in nature. I have written about them here and here. They are wonderful biochemical examples of evolution in action. The biochemistry is fascinating, but the wide variety of behaviors that animals use to make use of such venoms is equally remarkable.

For example, these scorpions are sometimes called “spitting” scorpions for a reason. They can spray venom against a potential predator, and that is not even the coolest thing about it!

Have you ever heard the expression “to rub salt in the wound“? This refers to the quite painful sensation that one feels when salty substances enter the broken skin.

It seems that the spitting scorpion has heard the expression too.

In a paper published in 2003:

Inceoglu et al. (2003) One scorpion, two venoms: prevenom of Parabuthus transvaalicus acts as an alternative type of venom with distinct mechanism of action. Proc Natl Acad Sci USA. 100(3):922-7.

scientists of the University of California at Davis reported that P. transvaalicus is able to produce a “prevenom” composed mainly of simple salts such as potassium chloride. You can access the paper free of charge here.

Essentially, when a predator, say a mouse, starts nibbling on the scorpion with the worst intentions, the scorpion will initially sting the mouse with the prevenom. Specifically, the scorpion is always “preloaded” with the prevenom. Such a salty solution will not likely kill the mouse, but it would sting like heck and will usually suffice to make the attacker go away. If the mouse is hungry enough though, it will continue biting the scorpion, and this continuous annoyance will cause it to make the real deal, venom containing the really nasty toxins.

Slide1

In the picture above, please note that the prevenom is a much clearer solution, as opposed as the milky appearance of the actual venom.

This seems to be an economic strategy. From the perspective of the scorpion, It is much more metabolically expensive to make protein-based toxins, etc., as opposed to make a simple salt solution. This makes sense, especially since these animals live in arid conditions, where resources are rather scarce.

Brilliant.

This phenomenon of different venoms produced by the same organism is not exclusive of scorpions. Some cone snails are also able to do this. I haven’t heard of other examples, but I am absolutely sure that there will be others. Nature is always surprising us. And all of this in only one planet! Can you imagine what could be “out here”?

IF YOU WANT TO KNOW MORE

Inceoglu et al. (2003) One scorpion, two venoms: prevenom of Parabuthus transvaalicus acts as an alternative type of venom with distinct mechanism of action. Proc Natl Acad Sci USA. 100(3):922-7.

Nisani et al. (2012) Investigating the chemical profile of regenerated scorpion (Parabuthus transvaalicus) venom in relation to metabolic cost and toxicity. Toxicon. 2012 Sep 1;60(3):315-23.

Prator et al. (2014) Venom variation during prey capture by the cone snail, Conus textile. PLoS One. 2014 Jun 18;9(6):e98991.

Dutertre et al (2014) Evolution of separate predation- and defence-evoked venoms in carnivorous cone snails. Nat Commun. 2014 Mar 24;5:3521.

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