Venom


The venom of scorpion is what causes widespread fear and fascination for scorpions. The prospect of such a tiny creature having such potent venom is both alluring and repulsive. Myth, legends, folklore, Hollywood and adoring parents tends to sensualise and exaggerate the effect of scorpion's venom. True enough, some scorpion species venom can be equated to that of the cobra. Still others, matches that of Black Widow spiders, brown recluse and other 'horrors'. However, if taken into context, few would believe that they would not die or indeed suffer serious ill effects from most of the scorpion species stings. Even stings from the supposedly highly dangerous ones are seldom fatal though these definitely are not to be taken lightly.
It is my wish that the general reader understand this fact after reading. The words in white are the less technical aspects while those in green are for those who wish to dabble in further. Be warned that there is wide usage of certain technical terminology which is unavoidable.
The aspects covered are:

  1. Foreword
  2. The probable reasons for development of venom in scorpions.
  3. The medically important species.(!! highly graphic intensive)
  4. Other important points to consider(and explanation of some terms)
  5. The components of scorpion venom
  6. Anaphylactic shock
  7. The common local and systemic effects (symptoms)
  8. The relative potency of venom to mice with comparisions to other animals
  9. What to do when stung by a scorpion

Foreword

Much of the common questions about scorpion venom is covered well by Dr Stockwell's FAQ about scorpions. I am but an amateur and do not pretend to know very much about venom and definitely can't compare with his knowledge. I am also not a physician (though I know a little medical science) and is thus not officially qualified to diagnose or treat scorpion stings. What I attempt to do here is to cover some things Dr Stockwell may not have covered fully and adding some viewpoints of others and myself.

For those who gets groggy from technical details, avoid the anaphylactic shock and components of venom sections.

The information here is compiled from many books with special attention to 'Venomous and poisonous animals' by G.G. Habermehl, 'Medical Entomology', 'Venomous and poisonous animals' by Anders Edstrom, ' Bites and Stings' by John Nicol, 'Arachnida' 1st edition by Savory, 'Toxic proteins derived from scorpion venom' by Zlotkin and 'Scorpionism in Mexican states' by Mazotti and Bravo-Becherelle. Internet resources includes Dr Stockwell venom section, CEVAP abstracts on Tityus spp venom, Dr Nils Bergman article on O.glabrifons envenomation, Scorpion sting syndrome (ten years experience) by Ken Dittrich, Anthony P. Power, Norman A.Smith.

I do not hold any responsibility for misrepresentation, falsehood and any damage or death caused from reference to the information stated here.

Probable reasons for development of venom in scorpions
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Things to clear up before proceeding.

To many people, there's no distinction between being venomous and poisonous. Even some past experts use them interchangeably. However, in more recent times, this two terms are commonly accepted by experts in toxicology to have different meanings.

Venomous:
It is commonly accepted that being venomous is being capable of producing, storing and delivering toxin. It is commonly associated with toxins being actively injected and the venom may not have any effect if consumed. However, a twist to this definition is a term used by some called secondary venom. It is used when animals like hedgehog rubs a poisonous toad on the spines and become 'venomous'. It is then capable of delivering the exogenous toxin to the molester. This, however, is not accepted by everyone.

Poisonous:
It is commonly accepted being capable of producing and storing the toxin. It is usually not actively delivered ,as opposed to venomous animals, and the toxin if consumed is harmful. Dendrobatids (poison arrow frog) fits this definition. There is yet another term used, secondary toxicity. It is usually applied to animals which consumes poisonous substances and become poisonous themselves. It is common among animals which become poisonous when they consume the poisonous red algae (red tide) and survived. They become poisonous to consumption. Yet further confusion is caused by the fish in Tetraodontidae (puffer fish). Contrary to what many (myself included) used to think, they do not themselves produce toxin. It is the enteric bacteria which produce the tetrodotoxin. This may be considered as a form of secondary toxicity. Another problem is that some puffer fish and frogs are capable of excreting/secreting the poison (toxin) when threatened or stressed. When this comes in contact and enters the body, the toxin exerts its effect. This blurs the boundary between being venomous and being poisonous

>>.

Scorpions do not possess venom primarily to kill people. Development of venom is seen in all major forms of life with an exception in the Aves (birds). It is obvious the evolution is more typical of convergence or parallel development in both different classifications and locality. The more well known venomous animals are snakes, centipedes, bees, spiders and scorpions. Nevertheless, if one examine more closely, most phylum/class possess some venomous or poisonous members. The more well known examples are

With even such a limited list, one roughly get an idea about how widespread venom is in animal kingdom. So why develop venom?
A rather simplistic view would be presented here for the general reader. Venom in general serves two purposes
1) To acquire food
2) For self defense

1) Food acquisition

It is obvious that venom is a very effective prey suppression tool. It is well employed by snakes to suppress large preys. The typical venomous snake (esp. vipers) bites its prey, release its venom and within split second let it go. It later search for the dead animal. I'm not straying from the subject here. We witness from here that venom can be an effective tool for predators not well equipped with grasping tools for suppression of potentially dangerous prey. So why in scorpions do venom develop?

Scorpions are well equipped with formidable pincer like pedipalp and many question why they should, at the same time, be venomous. In my view, most scorpions in the wild are opportunistic predator. Most lack the speed of insects like tiger beetles and as such must not be overly choosy in their prey selection. As such, relatively large prey like mouse and large beetles will also be fair game for a relatively large scorpion. In such case, the pedipalps may prove insufficient to quickly dispatch a struggling prey. Venom ,which is natures equivalent of chemical warfare, is the answer.

To further this hypothesis, we see that in most scorpions, the development of pedipalp is inversely related to the dependency on venom. In species like Emperor scorpion (Pandinus imperator), the pedipalp is greatly enlarged and the metasoma is not very well developed.
We also witness two other traits. a) Its venom is relatively weak b) It rarely stings its prey.
In most Buthidaes eg. Fattailed scorpion Androctonus australis, the pedipalp is slender while the metasoma is enlarged as the name suggest. The potency is also some of the highest among scorpions and it has great propensity to use its sting.It must be justified that the bulbousity of the pedipalp is not in direct inverse relationship with potency. A.australis has more bulbous pedipalp than A.bicolor but is not any less venomous

A second advantage of venom is that in many venom, enzymes are a major constituent. Enzymatic digestion before consumption is obviously an advantage which cannot be overlooked. This is especially apparent when considering viper's haemotoxin and phospholipase A2 content. As for scorpion venom, this may not be of equally significant role and thus far only Heterometrus scaber is positively shown to have haemolytic factor in its venom.
We see here a positive selection pressure for venom in scorpions especially for slender pedipalp species.

2) Defense

It is obvious to those attempting to handle scorpions that their venom is an effective defense. It serves one of deterence and incapacitation. The hissing (from chelicera stridulation) and aggressive defense posture combined is usually enough deterrence to most animals (including most people). When deterrence prove inadequate, a scorpion has to defend itself and incapacitation by venom is one such option. To support this claim, we see that a scorpion's venom is an cocktail of different toxins and other compounds. In Fat tailed scorpion, Androctonus australis, mammalian toxin I and toxin II is selectively effective against vertebrates. This can hardly be explained by their food choice (most of it being invertebrates). This therefore suggest a possible selective pressure for venom development against potential mammalian predators. It cannot be discounted at this point that it also helps to acquire vertebrate prey as well. Also if food acquisition is the main selective pressure for venom against vertebrates, it should follow that larger species like Pandinus imperator should have higher composition of vertebrate toxins. This apparently is not the case, giving me a better case for defense.

The hypothesis for deterence is supported by the composition of venom. Besides the other pathological and physiological effects, serotonin which is a constituent of scorpion venom also cause pain. This acts much like apamin's pain causing effect in bees. This is in fact is one of the most important property of venom, pain. It is more immediate and the offending animal immediately gets the message and may live to communicate it to others. In fact, in most case, what causes pain is not what causes death in the cocktail of substances in the venom. Neurotoxin, the common toxin type responsible for death, in fact mostly cause numbness initially.

With all these factors in favour of venom, one may wonder why not ALL organisms are venomous. Venom do have its advantages especially for smaller animals. I feel that generally smaller invertebrates employ venom more than vertebrates with exception of snakes. However, in active 'warm blooded' (homeothermic) animals like mammals and birds, it is downplayed. Part of the answer may lie in the fact that venom production is very expensive physiologically. With much higher consumption rate in homotherms, non-expendable tools like claws and dentition is selectively favoured. This again is my own hypothesis.
We see here that scorpion venom is definitely not selectively targeted against man.

A possible alternative use of venom may be seen in Hadogenes spp whereby the male has ridiculously elongated tails. I seem to have heard accounts of the male using the sting to cause slight hypnotic effect to the female during mating. That's unsubstantiated and dug up from some dark recess of my memory (no, not from Stockwell's page) so don't take my words for it.

With such a brief overview, I leave the reader to find out more and form his own conclusions.


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