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Scorpion

A scorpion is an invertebrate animal with eight legs belonging to the order Scorpiones in the class Arachnida, in the subphylum Chelicerata of the phylum Arthropoda.

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Physical characteristics

Scorpions are distinguishable at a glance from all the other arachnids by having the last five segments of the body modified to form a highly flexible tail, armed at the end with a sting consisting of a vesicle holding a pair of poison glands, and of a sharp spine behind the tip of which the ducts of the glands open. Like spiders they have four pairs of walking legs; but the limbs of the second pair form a couple of powerful pincers, and those of the first pair two much smaller flippers. They feed entirely upon animal food, principally upon insects such as beetles or other ground species, although the larger kinds have been known to kill small lizards and mice.

The sting

The large pincers are studded with highly sensitive tactile hairs, and the moment an insect touches these he is promptly seized by the pincers and stung to death, the scorpion’s tail being swiftly brought over his back and the sting thrust into the struggling prey. Paralysis rapidly follows, and, when dead, the insect is pulled to pieces by the small nippers and its soft tissues sucked into the scorpion’s mouth. Scorpions vary in size from about 2cm to 20cm; and the amount of poison instilled into a wound depends mainly on the size of the animal, though the poison of some of the smaller species is more virulent than in the larger species. On humans the effect of the poison is rarely fatal, though death has been known to follow in patients already in poor health.

In small scorpions, like those belonging to the genus Euscorpius[?], which occurs in Italy and other countries of South Europe, the sting is said to be as bad as that of a wasp; but in many tropical species acute pain, accompanied by inflammation and throbbing of the wounded part, follows. However, unless molested, scorpions are perfectly harmless, and only make use of the sting for the purpose of killing prey.

Suicide myth

The belief that scorpions commit suicide by stinging themselves to death when tortured by fire is of considerable antiquity and is prevalent wherever these animals occur. It is nevertheless entirely false, since the venom has no effect on the scorpion itself, nor on any member of the same species.

Growth

Unlike the majority of Arachnida, scorpions are viviparous. The young are born two at a time, and the brood, which consists of a dozen or more individuals, is carried about on its mother’s back until the young are large and strong enough to shift for themselves. The young in a general way resemble their parents and undergo no metamorphosis with growth, which is accompanied by periodical casting of the entire skin. Moulting is effected by means of a split in the integument which takes place just below the edge of the carapace all round, exactly as in kingcrabs, spiders and Pedipalpi. Through the split the young scorpion gradually makes its way, leaving the old integument behind.

Origins

Scorpions are of great antiquity. Their remains are often found in coal deposits of the Carboniferous Period, and no essential structural difference has been discovered between these fossils and existing forms—a fact proving that the group has existed without material structural modification for untold thousands of years. These Carboniferous scorpions were preceded by others, now occurring in marine Silurian deposits, which evidently lived in the sea and exhibit some anatomical differences marking them off as a group distinct from their Carboniferous and recent descendants and attesting affinity with the still earlier marine Arachnida referred to the group Gigantostraca[?]. Their legs were short, thick, tapering, and ended in a single strong claw, and were well adapted, it seems, like the legs of shore-crabs, for maintaining a secure hold upon rocks or seaweed against the wash of waves. The method of breathing of these ancient types is not certainly known; but probably respiration was effected by means of gills attached to the ventral plates of the body. At all events no trace of respiratory stigmata has been detected even in well-preserved material. These Silurian scorpions, of which the best-known genus is Palaeopzonus, were of small size, only 2-5cm in length.

Geographical Distribution

Scorpions are almost universally distributed south of 45°N and their geographical distribution shows in many particulars a close and interesting correspondence with that of the mammals, including their entire absence from New Zealand. The facts of their distribution are in keeping with the hypothesis that the order originated in the northern hemisphere and migrated southwards into the southern continent at various epochs, their absence from the countries to the north of the above-mentioned latitudes being due, no doubt, to the comparatively recent glaciation of those areas. When they reached Africa, Madagascar was part of that continent; but their arrival in Australia was subsequent to the separation of New Zealand from the Austro-Malayan area to the north of it. Moreover, the occurrence of closely related forms in Australia and South America on the one hand, and in tropical Africa and the northern parts of South America on the other, suggests very forcibly that South America was at an early date connected with Australia by a transpacific bridge and with Africa by a more northern transatlantic tract of land.

In conformity with their wide dispersal, scorpions have become adapted to diverse conditions of existence, some thriving in rainforests, others on open plains, others in sandy deserts, and a few even at high altitudes where the ground is covered with snow throughout the winter. In the tropics they aestivate at times of drought; and in the Alps they pass the cold months of the year in a state of hibernation.


See also USS Scorpion, CSS Scorpion, HMS Scorpion, Scorpius, The Scorpions rock band.



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