Scorpions are eight legged venomous invertebrates belonging to the class Arachnida, and the order Scorpiones. They are related to spiders, mites, ticks, and harvestmen as well as other members of the Arachnida class. They possess an extended body and a segmented, erectile tail ending with the telson (the sting). There are roughly 1,300 species of scorpions worldwide.
The scorpion's body has two parts, a cephalothorax which contains the prosoma, or head; and the abdomen. The cephalothorax is covered by the carapace, a hard bony or chitinous outer covering. The carapace usually suports a pair of median eyes at the top center. Two to five pairs of lateral eyes are found at the front corners of the carapace, though a few cave and montane forest litter-dwelling scorpions are eyeless. Chelicerae, the scorpion's mouthparts, and a pair of pedipalps, or claws used for prey capture and mating complete the head anatomy. The pedipalps are covered with trichobothria, sensory setae, that sense air-borne vibrations.
The abdomen is made up of the mesosoma, the main body, and the metasoma, the tail. The mesosoma, protected by bony armour, contains the lungs, digestive organs and sexual organs, as well as bearing 4 pairs of walking legs and the pectines. The tips of the legs have small organs that detect vibrations in the ground. The pectines are feathery sensory organs which hang beneath the abdomen and trail on the ground. They are coated by chemosensors that provide detection of minute chemical signals that are thought to alert the scorpions to the approach of prey and also to be of use in mating behavior. The respiratory structure, known as "book lungs," are spiracles that open into the scorpion's body. The surfaces of the legs, pedipalps, and body are also covered with thicker hairs that are sensitive to direct touch.
The metasoma curves up and ends in the telson, which bears the bulbous vesicle containing the venom glands and a sharp, curved aculeus which delivers the venom.
Most species of scorpions reach adulthood at a length of between 2 and 3 inches.The longest scorpion in the world is probably the African Scorpion (Hadogenes troglodytes) which grows to over 8 inches in length. In the U.S., members of the genus Hadrurus (giant desert hairy scorpions) are probably the largest, growing to a length of about 5 inches.
Range & Habitat
Though most prolific and diverse in warm habitat, scorpions have adapted to a wide range of environments, including plains and savannahs, deciduous forests, mountainous pine forests, rain forests and caves. Scorpions have been found at elevations of over 12,000 feet in the Andes Mountains in South America and in the Himalayas of Asia, as well as the Alps. In snowy areas, they hibernate during the cold months of the year. In drought areas they may aestivate (pass the summer in a dormant or torpid state).
About 90 species are found in the U.S. All but four of these naturally occur west of the Mississippi River. Scorpions are most common in southern Arizona and in parts of Texas and central Oklahoma.
Scorpions are nocturnal. They often ambush their prey, lying in wait as they sense its approach. They consume all types of insects, spiders, centipedes, and other scorpions. Larger scorpions may feed on vertebrates, such as smaller lizards, snakes, and mice if they are able to subdue them. They capture their prey with their pedipalps, paralyzing them with their venom as well if necessary. The immobilized prey is then subjected to an acid spray that dissolves the tissues, allowing the scorpion to suck up the remains.
As well as being predators, scorpions are also prey. Many types of creatures, such as centipedes, tarantulas, insectivorous lizards, birds (especially owls), and mammals, including shrews, grasshopper mice, and bats hunt scorpions for food.