Order Scorpionida

Scorpions are found in the tropics and sub-tropics. There are more than 1400 different species. The biggest is the imperial scorpion from West Africa which is 21 cm long. The smallest are just a few mm in length. However during the Silurian and Devonian there were giant aquatic scorpions around 2 metres long. One of these giants can be seen today in the Natural History Museum in London.

Right, Euscorpius flavicaudis. It a fairly common scorpion in southern Europe, and there are a few small colonies established indoors in the UK. It lives in crevices in rocks and walls grabbing anything small that passes close by.

The body.
Their long tail, usually has five segments, ends in the venomous sting. The sting is a bulbous base ending in a sharp, curved barb. Usually the potency of the venom is inversely proportional to the size of their pincers. So the smaller the pincers the stronger the poison. The venom of most scorpions, as far as man is concerned, has a similar potency to that of a wasp. However some have poison potent enough to kill a

human. The venom of Androctonus australis (see below), which inhabits the Sahara, is as toxic as a cobra's, and can kill a dog in seven minutes, and a human in 6 - 7 hours. The sting can be used to paralyse prey, but its primary function is defence.

Scorpion venom and cancer. In medical trials the venom of the Middle Eastern scorpion Heiurus quinquestriatus is being used to deliver radioactivity directly to cancerous tumours in humans. The venom is non-toxic to humans, and binds to a receptor found on tumor cells. So makes a perfect delivery system as it bypasses healthy tissue.

The pedipalps are large and end in pincers, and the legs in a pair of claws (see above). Some species can make a hissing sound by rubbing their claws against their legs.

They have between three and six pairs of simple eyes located around their carapace giving them all-round vision, as well as a pair of compound eyes facing the front. Although most scorpions have weak sight, and some are blind.

Pectines (see Androctonus australis left and below) are chemo-sensory appendages, and they consist of three rows of chitinous plates ending in comb-like teeth.

On the left is Pandinus imperator, the emperor scorpion found in African tropical and rain forests. It inhabits burrows up to 30 cm long. Its

sting is painful, but the poison is only mildly venomous, and cannot kill an adult healthy human. It can grow as long as 20 cm and has a life span of around eight years. Pandinus imperator is popular as a pet scorpion, and it will kill and eat anything it can catch.

Scorpions are real survivors, they can return to life after being frozen for weeks and can survive being submerged for two days. Some species can live without eating for a year. They are also long-lived; with some living for 30 years.

Feeding
All scorpions are carnivorous hunters and can detect the footfall of a beetle or the wing beat of an insect more than one metre away, but many of them tend to sit and wait until something wanders near before attacking.