Whip Scorpions look like their cousins the Scorpions, except that they have a long slender tail, it is this 'caudal appendage' which gives the group its name. They are mostly tropical in distribution with the largest species being found in the genus Mastigoproctus which is only found in America, other genera are Hypoctonus in Malaya, Typopeltus in Chochichina and Japan, and Thelyphonus in various parts of the Indo-pacific region. In captivity they tend to be very aggressive to one another and it is only possible to keep them in individual cages. When disturbed they will often discharge a gas from their back end that is said to smell of Acetic Acid (vinegar) in some species and Chlorine in others. This production, usage and smelling of acetic acid has resulted in their being called 'Vinergarones' in southern USA and the West Indies. In Taiwan Thelyphonus skimkewitchii is known as 'Mengpon-menn' or the 'Stinking Scorpion'.
Whip Scorpions are much larger than the similar looking Palpigradi, ranging in size from 25 to 70mm in length, Unlike the more common arachnids Whip Scorpions have no poison glands and their chelicerae are not chelate (i.e. they do not work like pincers as they do in many other arachnids) and kill their prey by crushing them. They are also unusual in that they use their long thin front legs as feelers, in much the same way that insects use their antennae, for this reason their front legs are referred to as 'antennaeform'. They have four pairs of rather weak simple eyes. Their abdomen has 12 segments, the last three of which are small and form a small plate called a 'pygidium', from which the tail or 'caudal appendage' extends.
Whip Scorpions are purely nocturnal hunters feeding mostly on insects such as cockroaches and grasshoppers, though they also eat worms and slugs. The prey is siezed between the two pedipalps and crushed between special teeth on the inside of the trochanters (the second segment of the leg) of the front legs. The large American Mastigoproctus giganteus carries its prey back to its burrow to eat and has been known to feed on small frogs and toads. They will readily drink water, at least in captivity. They spend the daylight hours in holes under rocks and stones which they dig using their large pedipalps.
Mating involves a brief courtship which begins with the male holding the females antennaeform forelegs in his pedipalps with their tips in his chelicerae and walking backwards until the female raises her abdomen. It then progresses to his stroking her genital segment with his antennaeform forelegs and the top of her abdomen with his chelae. Finally the male produces a spermatophore which he holds against the females genital aperture for several hours.
The pregnant female digs a special burrow with a larger area at the end, when the eggs are laid they are inside a special membrane that prevents them from drying out. The female remains in the end of her burrow guarding the eggs. When the eggs hatch the young are white and look nothing like their mother, they climb onto her back and attach themselves there with special suckers. After a while they moult and the creature which now emerges looks like a miniature Whip Scorpion. They soon leave their mother, who, now exhausted having spent so long without food, dies. The young are slow growing and go through three moults in about three years before they reach maturity.