Scorpions (order Scorpiones) are predatory arachnids with eight legs, a pair of grasping pincers and a narrow, segmented tail, often carried in a characteristic forward curve over the back and always ending with a stinger. The evolutionary history of scorpions goes back 435 million years. They mainly live in deserts but have adapted to a wide range of environmental conditions, and can be found on all continents except Antarctica. There are over 2,500 described species, with 22 extant (living) families recognized to date. Their taxonomy is being revised to account for 21st-century genomic studies.
Scorpions primarily prey on insects and other invertebrates, but some species hunt vertebrates. They use their pincers to restrain and kill prey, or to prevent their own predation. The venomous sting is used for offense and defense. During courtship, the male and female grasp each other's pincers and dance while the male tries to move the female onto its sperm packet. All known species give live birth and the female cares for the young as their exoskeletons harden, transporting them on its back. The exoskeleton contains fluorescent chemicals and glows under ultraviolet light.
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