<P> See classification for families . </P> <P> Scorpions are predatory arachnids of the order Scorpiones . They have eight legs and are easily recognized by the pair of grasping pedipalps and the narrow, segmented tail, often carried in a characteristic forward curve over the back, ending with a venomous stinger . Scorpions range in size from 9 mm / 0.3 in . (Typhlochactas mitchelli) to 23 cm / 9 in . (Heterometrus swammerdami). </P> <P> The evolutionary history of scorpions goes back to the Silurian period 430 million years ago . They have adapted to a wide range of environmental conditions and can now be found on all continents except Antarctica . Scorpions number about 1750 described species, with 13 extant (living) families recognised to date . The taxonomy has undergone changes and is likely to change further, as genetic studies are bringing forth new information . </P> <P> All scorpions have a venomous sting, but the vast majority of the species do not represent a serious threat to humans and in most cases healthy adults do not need any medical treatment after being stung . Only about 25 species are known to have venom capable of killing a human . In some parts of the world with highly venomous species human fatalities regularly occur, primarily in areas with limited access to medical treatment . </P>

How many different types of scorpions are there