The life and times of African scorpions.
Scorpions are arachnids, not insects, and they sting, rather than bite. They may be recognised by their eight legs, two pincers, and segmented tail, often carried curved over the back. Other ways in which arachnids differ from insects are that they have a fused head and thorax called a cephalothorax, whereas these body segments are separate in insects as they are in man; scorpions never possess wings or antennae and do not sport compound eyes. The vast majority are not dangerous to man.
Evidence from the fossil record tells us that they've been around since the Silurian period, around 430 million years ago; they are efficient predators and have had no need to undergo any marked evolutionary changes.
They are exoskeletal, and possessing an external skeleton is one of the features that limits the size they can attain--though Hadogenes troglodytes from southern Africa can attain a length of 20cm and Heterometrus swammerdami found in India grows to a record size of 23cm. The largest scorpion I have ever seen was a 14cm troglodytes found in a Harare suburb, and it was indeed an impressive sight.
Scorpions found south of the Zambezi River have probably been studied more extensively than anywhere else on the Dark Continent. They are represented by four taxonomic families, only one of which possesses a venom that is dangerous to man.
The family Scorpionidae is represented in Africa by the genus Opistophthalmns, which numbers just under a hundred species. Commonly known as burrowing scorpions, they dig deep and fairly complex burrows. They have bulky, powerful chelae, or pincers, which are their primary means of subduing prey, and they are not thought to venture out from their burrows except to mate. This results in very few encounters with man, and a relative scarcity of stings. The sting can be painful, much like a bee sting, but except in the case of O. glabrifrons, whose venom has been reported to cause unpleasant systemic effects, they are not dangerous to man.
Liochelidae is the family to which the so-called thin-tailed scorpions belong; it is represented in southern Africa by the genera Opisthacanthus, Hadogenes, and Cheloctonus. Known as creeping scorpions, the Opisthacanthus can be found on mainland Africa and Madagascar, and while it can be temporarily painful, their sting is of no consequence to man. Flat rock scorpions of the genus Hadogenes only occur in southern Africa, spanning South Africa, Namibia, Botswana, Zimbabwe and Mozambique. They, too, rely on their relatively large pincers to subdue prey, not their venom. I have been stung on occasion by Hadogenes; it is not pleasant, but there are no systemic effects and no local symptoms like oedema and necrosis. Walking barefoot at night is an open invitation for the little brutes. Cheloctomis are found in South Africa, Mozambique and Lesotho and as they are also burrowers, they rarely cross paths with man. Their stings are briefly painful and otherwise nothing to worry about.
The family Bothriuridae is only found in northern Namibia, and the two species of the genus Liposoma possess extremely slender tails--which distinguish them from similarly-coloured Buthids--and they are of no medical significance to man. L. joseehermana is a burrower, and L. elegans seeks refuge under stones.
Now for the bad guys.
The family Buthidae is found on every continent except, surprise surprise, Antarctica. They are recognised to be dangerous to man, and the most virulent genera are Parabuthus and Buthotus.
Parabuthus can be distinguished by a thick and prepossessing tail and relatively small pincers, which are not heavily relied upon to subdue prey because of the potency of the quick-acting venom. The largest can measure up to 14cm in length, and are normally burrowers, digging in at the base of shrubs or under other ground cover such as logs or rocks. All species of Parabuthus should be considered to be potentially lethal to man, and in certain parts of South Africa, specifically in the northwestern Cape, they are more of a problem than venomous snakes. Also, interestingly, like Africa's spitting cobras and ringhals, some species of Parabuthus are believed to be able to "spit" or project their venom--though this still needs to be conclusively documented.
Scorpion venom in general consists of water, inorganic salts, peptides, and proteins, with the peptide fractions being the most biologically active. Specifically, they target ion channels in the cells of the prey. Ion channels are the parts of cell membranes that regulate the flow of ions. Because ions are charged particles, e.g. sodium (Na+) or chloride (C1-), this flow of ions can be used to polarise a membrane and create a resting potential which alternates with action potentials. Probably the most well-known example of this is in neurones, or nerve cells. When the action potential is generated, a nerve impulse is created. Mess with the cell's ability to generate an action potential by disrupting the function of the ion channels, and you can shut down both voluntary and autonomic nervous system functions.
Parabuthus transvaalicus is especially interesting because it produces two types of venom. The first drop out of the sting is a "pre-venom", which has a different molecular structure and effect than the rest of the toxin. The pre-venom is thought to be used chiefly to deter predators, but further study is required.
The pre-venom is at once more effective and less potent that the venom itself. This has a number of significances. The proteinaceous nature of the venom means that it is metabolically "expensive" for the scorpion to produce. The pre-venom is typically secreted as an immediate response to a threat, which can be followed up "for real" by an injection of venom if need be; the pre-venom is less metabolically demanding to produce because of its lower protein content. While the pre-venom contains less protein, it does contain much higher levels of potassium (K+), which is easier to replace and very efficacious on ion channels.
Aside from that, male scorpions often sting the females repeatedly during mating; if the pre-venom is used here, it could stimulate the female without exposing her to the harmful effects of the venom itself.
The medical treatment for a scorpion sting can be every bit as complex as for a snakebite. Since most species are not of medical significance, envenomation can be treated symptomatically, e.g. plenty of fluids and a mild analgesic. For species which are potentially lethal, often antivenin will be available, and the use of antivenin comes with its own challenges.
If you get stung by a scorpion you will probably experience a tingling or burning pain at the site of envenomation. The first time I got zapped by a Hadogenes, I felt a sharp stabbing pain that would recur every few minutes and this lasted throughout the night and into the next morning. There was no swelling, or any other marked symptoms. Management of this type of sting can be done at home, and is no real cause for worry.
Gently wash the site of the sting with soap and water, and remove any jewelry near the sting in case there is some local swelling. Doctors recommend that you avoid the use of aspirin and ibuprofen, but acetaminophen (Tylenol in the United States or various brands of paracetamol in Africa) can be given as per the instructions supplied. Unless a secondary infection develops, antibiotics are not recommended. A cold compress may be applied ten minutes on and ten minutes off. In my case, all I did was wash my foot, take a couple of acetaminophen and try to get some sleep.
As with a venomous snakebite, do not cut into the wound, apply a constriction bandage or tourniquet or intense cryotherapy (cold treatment). Suction at the site of the sting is largely thought to be ineffective.
If the offending species is medically significant, symptoms may progress to a spreading numbness, difficulty in breathing, difficulty swallowing, blurred vision, and seizures. These symptoms may lead to death, and must be addressed by a medical practitioner as soon as possible. If antivenin therapy is required, this is best done by a doctor in a hospital, because the serum may be equine in nature and other problems like anaphylaxis may present themselves. A period of observation--usually 24 hours--will also be a good plan.
If you can, without risking another sting, collect the scorpion for later identification. One Christmas I was in a campsite at Lake Kariba and some very worried-looking South Africans came over one morning saying that their uncle had been stung by "this--what is it?" What was thrust under my nose was a small tupperware container that held what quite honestly looked like potpourri. It had at one time been a scorpion, but there wasn't much left from which to make an identification. Relative to everything it was a fairly thin tail and uncle lived happily ever after. Good thing too, for Tashinga is a long way from medical treatment.
Prevention, of course, is better than having to worry about a cure of any kind. Scorpions are nocturnal, so after dark, wear shoes, and when performing chores like collecting firewood wear gloves and use a light to clearly illuminate what you're doing.
As an aside, scorpions become luminescent under an ultraviolet light--a vibrant bluish green colour. Purpose-made "scorpion lamps" are commercially available for those who go in search of the critters. This facet of arachnology isn't yet fully understood. Preliminary experiments show that insects actually avoid the fluorescence, so not much help there. One intriguing theory is that they use this phenomenon to hide. The reasoning is that while they are predators, in terms of owls and rodents, they are also prey. This is why they like shelter. Douglas Gaffin from the University of Oklahoma believes they are converting the low-intensity UV light from stars and die moon into bluish-green light, which is what their sensitive eyes see best. He theorises that by sensing light with their bodies this way, they can easily "feel" a shadow cast by even a twig, which in turn represents cover and safety.
If you come across a scorpion on your African travels, consider yourself lucky--they are a lot more interesting than ominous.
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|Title Annotation:||African Perspectives: The Dark Continent in Discussion|
|Publication:||African Hunter Magazine|
|Date:||Jun 1, 2016|
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