There about 1100 species of scorpions known worldwide, and probably that many more still to be discovered. Although they are normally associated with hot, dry areas like deserts, scorpions are found in a variety of habitats including cool, wet forests and grasslands. Scorpions are among the oldest arachnids. The earliest fossils date from the middle Silurian rocks, over 400 million years old. Early scorpions had large compound eyes, but were otherwise similar to living forms.
Scorpions are generally large arachnids.
Adults range in size from 1.5 cm to 21 cm in length. All are predatory. Their prey includes a variety of arthropods and other invertebrates, and the larger species are known to prey on small vertebrates. The scorpion's most notorious feature is its poisonous sting. While all scorpions are venomous, only about twenty species worldwide possess venom of sufficient toxicity to kill humans.