Scorpions are arthropods distinguished by such striking features as large pedipalps furnished with stout claws, and an abdomen divided into two portions--a broad, seven-segmented preabdomen, and a five-segmented posterior with a slender tail ending in a sting. The base of the sting contains a pair of poison glands opening near the tip. Scorpions usually thrive in hot and tropical countries. They reach up to 100 to 125 mm (4 to 5 in) in length--some species taking years to attain maturity--and are nocturnal animals, concealed by day in protected places. Predatory carnivores, they feed on insects and spiders, capturing the prey with their pedipalps and killing with their sting. Jawlike appendages near the mouth crush the prey, over which the scorpion then discharges a digestive fluid and sucks up the liquefied prey. Young scorpions are born alive and are then carried on the mother's body for a short time. Few scorpions are dangerous to humans, and ordinarily they do not attack unless disturbed. The only species in the United States with a potentially fatal sting, Centruroides sculpturatus, is yellow to yellow brown with two black stripes on the back. The sting from most species produces pain and swelling. Serums are available to relieve the more severe symptoms. Scorpions are classified in the class Arachnida, phylum Arthropoda. There are six families--including the important Buthidae, which includes many common yellow species--and more than 30 species occur in the southern and western United States.

Bibliography: Cloudsley-Thompson, J. L., ed., Ecophysiology of Desert Arthropods and Reptiles (1991); Polis, G. A., ed., The Biology of Scorpions (1990).