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Order Scorpiones: Scorpions
Scorpions are perhaps the most ancient of terrestrial arthropods and comprise about 1400 species worldwide. Although scorpions are more common in tropical and subtropical regions, some occur in temperate zones. Scorpions are generally secretive, hiding in burrows or under objects by day and feeding at night. They feed largely on insects and spiders, which they seize with their pedipalps and shred with their chelicerae.
Sand-dwelling scorpions locate prey by sensing surface waves generated by the movements of insects on or in the sand. These waves are detected by compound slit sensilla located on the last segment of the legs. A scorpion can locate a burrowing cockroach 50 cm away and reach it in three or four quick movements.
Scorpion tagmata are a rather short cephalothorax, which bears chelicerae, pedipalps, legs, a pair of large median eyes, and usually two to five pairs of small lateral eyes; a preabdomen (or mesosoma) of seven segments; and a long slender postabdomen (or metasoma) of five segments, which ends in a stinging apparatus. Their chelicerae are small; their pedipalps are large and chelate (pincerlike); and the four pairs of walking legs are long and eight-jointed.
the mother until their first molt. B, Harvestmen, Mitopus sp. (order Opiliones). Harvestmen
run rapidly on their stiltlike legs. They are especially noticeable during the harvesting
season, hence the common name.
On the ventral side of the abdomen are curious comblike pectines, which serve as tactile organs for exploring the ground and for sex recognition. The stinger on the last segment consists of a bulbous base and a curved barb that injects venom. Venom of most species is not harmful to humans but may produce a painful swelling. However, the sting of certain species of Androctonus in Africa and Centruroides (Gr. kenteo¯, to prick,+ oura, tail, + oides, form) in Mexico can be fatal unless antivenom is administered. In general, larger species tend to be less venomous than smaller species and rely on their greater strength to overpower prey.
Scorpions perform a complex mating dance, the male holding the female’s chelae as he steps back and forth. He kneads her chelicerae with his own and, in some species, stings her on her pedipalp or on the edge of her cephalothorax. The stinging action is slow and deliberate, and the stinger remains in the female’s body for several minutes. Both individuals remain motionless during that time.
Finally, the male deposits a spermatophore and pulls the female over it until the sperm mass is taken into the female orifice. Scorpions are truly viviparous; females brood their young within their reproductive tract. After several months to a year of development anywhere from 1 to over 100 young are produced, depending on the species. The young, only a few millimeters long, crawl onto their mother’s back until after their first molt. They mature in 1 to 8 years and may live for as long as 15 years.
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