Scorpions

On this page, overview - scorpion body - feeding - mating and reproduction - venom - medicinal uses of scorpion venom

Order Scorpionida overview

Scorpions are found in the tropics and sub-tropics, and are mainly nocturnal, spending the day in hiding. There are almost 2000 different species described so far, ranging in size from 8.5 - 230mm long. The biggest is the imperial scorpion from West Africa which is over 21cm 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.

Scorpion body

The scorpions long tail, usually has five segments, and 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. For more on scorpion venom see below. Scorpions, like earwigs, are thigmotactic, i.e. they like to sleep and rest in location that are closely fitted to their body.

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

scorpion leg

Eyes. Scorpions have up to 12 eyes. Usually there are 2 large eyes, raised up and facing the front. Then 2 rows of smaller eyes on either side of the head area. However the cave dwelling species may have no eyes at all.

Pectines (see Androctonus australis below) are chemo-sensory appendages, and they consist of three rows of chitinous plates ending in comb-like teeth. The pectines are close to the ground surface, and as the scorpion moves they can touch the ground and sweep just over it. Each pectine has from 5 - 50 teeth, and each tooth is covered in thousands of sensory hairs.

Book lungs. Scorpions have 4 pairs of book lungs that open to the surface as spiracles. Some species are able to control the size of the spiracle opening, and so restrict water loss.

Androctonus australis ventral view

Euscorpius flavicaudis

Euscorpis flavicaudis, European scorpion

Above is 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 under rocks, bark and walls grabbing anything small that passes close by. Its body is dark brown/black, and it legs and sting are yellow/brown. It is not aggressive, and its poison has no effect on humans. It can reach 4cm long when fully grown, and makes a good choice as a pet for a beginner.

Pandinus scorpions

Scorpions in this genus are relatively large, with most being longer than 10cm, and they are usually black or dark coloured. They have a stridulatory (sound producing) organ which consists of a rough patch on their pedipalps which they scrape against a set of bristles on the first pair of walking legs. As with many large scorpions their venom is relatively mild, and is said to resemble a bee sting.

Pandinus imperator, the emperor scorpion

Pandinus imperator, emperor scorpion

Above is Pandinus imperator, the emperor scorpion found in African tropical and rain forests. It inhabits burrows up to 30cm long. Its sting is painful, but the poison is only mildly venomous, and cannot kill a healthy human adult. It can grow as long as 20cm 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.

Pandinus viatoris

Pandinus viatoris, Scorpion 

Pandinus viatoris above, like many scorpions, catches it prey by ambush.

Scorpion venom

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 the fat tailed scorpion (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. Around 8,000 people die each year as a result of scorpion stings in Mexico alone.

Androctonus australis

Scorpion venom is a neurotoxin, so affects the nerves causing paralysis of cardiac and respiratory muscles. The sting can be used to paralyze prey, but its primary function is defence. The venom exits the sting through 2 pores either side of the tip. The venom is produced by 2 glands at the base of the sting.

Medicinal use of scorpion venom

Scorpion venom and cancer. In medical trials the venom of the Middle Eastern scorpion Leiurus 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 tumour cells. So makes a perfect delivery system as it bypasses healthy tissue. It is also being trialled for operations to remove cancers in the brain. If the chlorotoxin is tagged with a fluorescent dye it will illuminate the tumour, thereby allowing surgeons to remove only the cancerous tissue, and leave the healthy brain tissue unharmed.

In bypass surgery scorpion venom is used to block a human-produced protein which replaces new blood vessels, and could block blood flow during the surgical process. (Cardiovascular Research, DOI:10.1093/cvr/cvq305.)

Scorpion Mating and reproduction

Scorpions mate at night. Pheromones attract mates and lead to the initiation of courtship. The male holds the female's pincers in his own. They both arch up their abdomens until their stings touch, then they dance. The dance lasts for a few hours to a few days! Mating occurs the following day. The male deposits a spermatophore on the ground and pulls the female over it until the sperm mass is taken up by her. After mating the the male is sometimes eaten by the female. A female can have from 6 - 90 young depending on the species and the quality of habitat, and the young are born fully formed. The young crawl on to their mother's back until after their first moult, during this time, which usually lasts around two weeks, the young do not feed.

Scorpion 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. This ambush predation is probably the most common feeding method in scorpions. The scorpion waits, perhaps in its burrow, or hiding place, or else staying still out in the open. Then when the prey comes within reach it is attacked. There are some species that do stalk their prey as well.

Scorpions are liquid feeders. Once they prey has been caught and dead or subdued, digestive enzymes are injected into its body from the scorpion's salivary glands. These enzymes liquidise the tissues which are then sucked up by the scorpion. Once a scorpion has eaten it will not emerge again for another two weeks to two months. In captivity some have gone twelve months between meals. The main prey items are insects, spiders, lizards, small snakes, and other scorpions. Scorpions are not fussy eaters, they will try to kill anything within reach.

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.