Today there are well over a thousand different species of scorpion and they can be found throughout the tropics and sub-tropics. The biggest of them, aptly called the imperial scorpion, lives in the humid rain forest of West Africa. Fully outstretched, it can measure 8 inches (21 cm). Some desert scorpions on the other hand are only a few millimeters long. All are very similar in form, with a pair of large and formidable pincers in front, eight legs, and a long segmented tail which is usually carried arched over the animal's back. At the end of it hangs a large tear-shaped stinger loaded with poison.

The potency of scorpion's poison varies - as does the reaction of different animals when stung. As a general rule, the bigger and more formidable a scorpion's pincers, the less virulent its sting is likely to be. So the imperial relies more on its strength to overcome the prey and has a comparatively mild sting, whereas smaller species with fat tails and thin pincers have a venom so virulent that their sting can kill a dog in seven minutes and a human being in a few hours.

Although scorpions are normally only found in warm countries, their tolerance to different climatic conditions is extraordinary. They can withstand freezing for several weeks and will survive underwater for two days. Their external skeleton retains liquid so effectively that they can live in the hottest deserts. Their appetite is so small that individuals of some species can go without any food or water for twelve months. And they have a life span of up to thirty years.

If you try to pick up a scorpion, you quickly realize that it is almost impossible to catch the animal unaware. One way to make the attempt is to take a pair of forceps and grip it by its tail, just beneath the sting. But this is not easy. No matter from which direction you approach, the animal will be aware if you and will swivel to face danger often jerking its stinging tail forward in a threatening way. Almost as alarming, some species, such as a greenish black one that lives in southern India, will hiss at you, producing the noise by rasping a small patch of tiny spines on its claws

They can see you which ever way you approach for they have up to six pairs of simple eyes distributed around their carapace, together with a rather larger pair close to its back margin. So a scorpion can see both forwards and backwards simultaneously. These eyes consist of a group of individual light-sensitive cells.

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But vision is by no means a scorpion's primary sense. It will certainly be aware of your approach even if it cannot see you. The slightest movement on sand causes a minute vibration that is transmitted from grain to grain. The scorpion detects it with a slit-shaped organ on the upper part of each leg. These are so sensitive they can detect the footfall of a beetle on sand when it is a meter away. Air-borne noises are picked up by scorpion in a different way - by minute hairs on the claws. With these it can detect the beat of an insect wing.

In addition to all these receptors the scorpion also has sensory devices that have virtually no parallel in any other animal - comb-like structures on the under-surface of its last pair of legs. They are called pectines and they are certainly sensitive for they are packed with nerve endings. It now seems certain that these organs are chemo-receptors. Whatever their precise role turns out to be, part of it will involve the smelling or tasting of chemical substances on the surface over which they walk.

[Photo of Israeli black scorpion (Scorpio maurus fuscus)]
Israeli black scorpion Scorpio maurus fuscus
A subspecies of Scorpio maurus
Photo courtesy of BioLib

Scorpions do not generally attack man and can be carefully brushed off the body without danger; but if they are suddenly disturbed they may inflict a painful sting. The sting of some species may even be fatal, particularly to children because of their small size. One of the more venomous species in the United States is Centruroides exilicauda commonly known as Arizona Bark Scorpion. This species was previously known as C. sculpturatus. The specific name exilicauda means "slender tail".

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