SCORPION, the name for the order Scorpiones of the Arach nida (q.v.), distinguished by having the last five segments of the body modified to form a flexible tail, armed 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. In addition, they have four pairs of walking legs; the second pair form powerful pincers, and those of the first pair smaller nippers. They feed principally upon insects although the larger kinds may kill small lizards and mice. The large pincers are studded with tactile hairs, and the moment an insect touches these he is seized by the pincers, the scorpion's tail brought over his back and the sting thrust into the prey. Scorpions vary in size from about 1 in. to 8 in. The poison is more virulent in some of the smaller than in the larger species. Upon mankind the effects of the poison are seldom fatal.
The belief that scorpions commit suicide by stinging them selves to death when tortured by fire is quite without foundation; the venom has no effect upon the individual itself, nor upon other members of the same species. Scorpions, however, succumb rapidly when exposed to the warmth of a fire or of the tropical sun. They are easily rendered innocuous by scraping off the sharp point of the sting; and it has been shown that immunity to the ill effects can be acquired by being repeatedly stung.
Many scorpions exhibit a conspicuous warning coloration of jet-black or black and yellow; and many have stridulating organs. These, like the rattle of rattlesnakes, advertise their presence and help to prevent their being attacked or trodden on. In habits they are nocturnal, spending the daytime concealed under stones or fallen tree trunks or in burrows. Amongst the burrowing kinds
are the large African species of the genera Pandinus and Opis thophthaltnus and the eastern genus Palamnaeus.
Scorpions are viviparous. The brood, which consists of a dozen or more young, is carried about on its mother's back until they are able to shift for themselves. The young resemble their parents and undergo no metamorphosis. Moulting occurs by means of a split just below the edge of the carapace as in king-crabs and spiders.
Scorpions were already in existence in the Carboniferous Period and there is no essential structural difference between these fossils and existing forms. These Carboniferous scorpions, how ever, were preceded by others, in Silurian deposits, which lived in the sea and exhibit differences marking them off as a distinct group and attesting affinity with the earlier marine Arachnida, known as Gigantostraca. Their legs were short, thick, and ended in a single claw, adapted for maintaining a hold upon rocks or seaweed against the wash of waves. These Silurian scorpions, of which the best-known genus is Palaeophonus, were only or 2 in. in length.
At the present time scorpions are almost universal south of the 4oth or 45th parallels of north latitude ; and their geographical distribution shows a close correspondence with that of the mammalia, their absence from New Zealand being an interesting point of agreement. Scorpions are adapted to diverse conditions, some thriving in tropical forests, others on open plains, others in sandy deserts, and a few at high altitudes with abundant snow in winter. In the tropics they aestivate at times of drought ; and in temperate latitudes they pass the cold months in hibernation.