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May 2003

Feature

 


Understanding scorpions

Jonathan Leeming

Parabuthus granulatus is southern Africas most venom scorpion. This is the typical striking pose of a scorpion. With the sting at the ready, this scorpion means business.Although scorpions are probably one of the most recognizable animals in the world, few creatures are as enigmatic or feared. Even in this modern world, misconceptions still perpetuate amongst most people. Scorpions are secretive creatures that usually retreat at the slightest disturbance. In many habitats they represent a major predatory force acting upon a variety of small creatures.

Scorpions evolved from aquatic creatures that lived some 450 million years ago, way before the dinosaurs existed. In those early days of evolutionary experimentation, they attained a length of over 1m. Scorpions have since then scaled down in size and have wedged themselves into their own niche habitats within the general environment.

Scorpion spotting - not in your shoe

It is difficult enough finding these creatures during the day, but at night it is a different story. When looking for scorpions scientists use an ultraviolet light. At night, under normal torch light (white light) scorpions are impossible to detect. Their cryptic colouration and ability to hide at the mere flicker of a light makes them difficult to locate. Under Ultra Violet (UV) light however, scorpions emit an eerie greenish glow. On dark nights small species can be seen from many meters away. It is not uncommon to see over 200 individuals in good scorpion habitats. We do not understand why they glow, but they do. "Unfortunately, warthog holes, barbed wire fences and large mammals do not glow under UV light making scorpion collecting an exciting pastime in big five country," jokes scorpion expert Jonathan Leeming.

"Survival guides to the outdoors always amuse me because they amplify the 'fact' that scorpions will crawl into you shoe if left outside," says Leeming. Even scarier was the suggestion by one book to always check under the toilet seat for scorpions. According to Leeming, the truth is that the average scorpion wouldn't find your shoe or sleeping bag an inviting place to shelter. Southern Africa does contain more than a few places where highly venomous species abound, and where leaving ones shoes, clothes outside is not advised. Stings from these highly venomous creatures are extremely painful but rarely fatal. Under certain conditions scorpions may leave their burrows or become nomadic.

The sting

All scorpions posses neurotoxic venom. Their venom is fundamentally similar and therefore antivenin can be applied across the board. Scorpion venom is a complex mixture of neurotoxins each part performs a certain function. Functions include pain-inducing components for warding off predators, or toxins aimed at immobilizing specific groups of creatures such as insects, and even courtship.

Southern Africa has an extremely low mortality rate when it comes to scorpion envenomations. On average a dozen or so fatalities are recorded annually. Thanks to the availability of good medical facilities and antivenom, deaths in southern Africa are few indeed, usually restricted to infants and the aged. These figures pale in comparison to countries such as Mexico where on average 2000 people die annually as a direct result of scorpion stings.

Hadogenes sp. are some of the worlds least venom scorpions. To make up for their weak venom they do sport a pair of powerful pincers. It is interesting to note that southern Africa is host to one of the world's least venomous scorpions belonging to the genus Hadogenes. Although Hadogenes sp. venom is virtually harmless they do sport a pair of powerful pincers capable of splitting fingernails. A member of this genus also holds the record for the longest scorpion in the world, attaining a length of over 21cm. A few more can even spray venom in defense. If the sprayed venom gets in the eyes it is a painful and visually impairing ordeal. Survival guides come to the rescue in this respect and recommend washing out with any bland fluid, even urine.

Pecking order

Scorpion population dynamics has long since fascinated Leeming. On early collecting trips it was clear that on some nights only certain species were found. On other nights other species abound. When contemplating this phenomenon it becomes easier to understand if you look at it from a scorpion's perspective.

The majority of southern African scorpions have eight eyes. Two median eyes found in the middle of the carapace and two groups of three eyes found at the front corners of the caparace.Scorpions have a pecking order. Maybe it should be called a "munching" order since large species of scorpion often prey upon smaller species. Although scorpions are immune to their own venom, their venom does have a significant effect across species. Depending on the species structure that exists within a habitat, these dominant species are aggressive hunters, often highly venomous and large in size. They prey upon the smaller species found in the same habitat. When these dominant species abound, smaller species tend to be unseen. This is not because they have all been eaten. They avoid being preyed upon by the more aggressive species by avoiding them and being active when conditions do not suit other species. Smaller species often hunt in vegetation, a place where large creatures find it hard to move through.

Hunting techniques play an important role in encounters with humans. The majority of species are opportunistic, preying upon anything they can overpower that comes within striking distance. Often species ambush their prey from the periphery of their shelters, be it a burrow, crack in a rock or tree. It is interesting to note that our two most venomous species have a wide distribution and their hunting techniques depart from the typical sit-and-wait style that most scorpions practice. Parabuthus transvaalicus and the more venomous Parabuthus granulatus are two species that actively forage for prey at night. They are almost arrogant in their foraging strategies as they march around seemingly defiant of human observation.

Habitat

Parabuthus mosambicensis sheltering in a hole in the sand.Many species have very specific habitat requirements. In some cases their distributions can be mapped back to rock types, sand systems and substrate composition. A good example of a close relationship is Opistophthalmus holmi which is confined to the Namib sand system in Namibia. Highly evolved specializations ideally equip this small scorpion to life in a sea of shifting sands. On sand, these specializations help the scorpion to walk, feed and hunt, however in foreign habitats this species would be like the proverbial fish out of water. Very few species have extensive distributions that extend over varying types of terrain and habitats. Species that invest time and energy into shelter construction would not leave their shelter easily. In habitats where shelters cannot be created they must be found in the natural environment, scorpions do not just abandon these for any reason. Although more scorpions can be found in the more arid parts of southern Africa, scorpions can be found in almost every terrestrial habitat except the high mountain peaks of Lesotho.

Scorpions have incredibly slow metabolic processes which enable them to wait out unfavourable conditions. It's estimated that some burrowing species spent up to 95% of their entire life inside their burrow. Other experiments describe how a scorpion was frozen in ice and remained relatively unharmed after a bit of defrosting. Some species rarely drink water as their prey contains all their water requirements. Other species have been known to go without food for more than a year. During the winter months in southern Africa, scorpions are often very difficult to find. Burrowing species simply close up the entrance to their burrows and wait for conditions to improve. When conditions are right, mass emergents of scorpions often described as plagues occur. Factors such as rainfall and temperatures are often the cue for such events.

Through no fault of their own, scorpions have a bad reputation. It seems like the only time we hear about these creatures is when someone is stung or even dies. Beyond their venomous tendencies lie complex behavioural patterns and intricate lifestyles. As scientists delve deeper into the private lives of these creatures we can only learn from these living fossils and develop a greater understanding of these fascinating creatures.


More information:

Jonathan Leeming:

Jonathan@scorpions.co.za

http://www.scorpions.co.za




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