|Hottentotta tamulus from Mangaon, Maharashtra, India|
C. L. Koch, 1837
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). 
The evolutionary history of scorpions goes back to the Silurian period 435 million years ago. They have adapted to a wide range of environmental conditions, and they can now be found on all continents except Antarctica. There are about 1,750 described species,  with 13 extant (living) families recognised to date. Their taxonomy is being revised in the light of genomic studies.
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. 
The word " scorpion" is thought to have originated in Middle English between 1175 and 1225 AD from Old French scorpion,  or from Italian scorpione, both derived from the Latin scorpius,  which is the romanization of the Greek word σκορπίος – skorpíos. 
Scorpions are found on all major land masses except Antarctica. Scorpions did not occur naturally in Great Britain, New Zealand and some of the islands in Oceania, but now have been accidentally introduced in some of these places by humans. The greatest diversity of scorpions are in subtropical areas and decreases towards both the poles and the equator.  Five colonies of scorpions ( Euscorpius flavicaudis) have established themselves in Sheerness on the Isle of Sheppey in the United Kingdom.  At just over 51°N, this marks the northernmost limit where scorpions live in the wild.  
Scorpions primarily live in deserts but can be found in virtually every terrestrial habitat including: high-elevation mountains, caves, and intertidal zones. However, they are largely absent from boreal ecosystems such as: the tundra, high-altitude taiga, and some mountain tops.   As regards to microhabitats, scorpions may be ground-dwelling, tree-living, rock-loving or sand-loving. Some species, such as Vaejovis janssi, are versatile and are found in every type of habitat in Baja California, while others occupy specialized niches such as Euscorpius carpathicus, which is endemic to the littoral zone of rivers in Romania. 
Scorpion fossils have been found in many strata, including marine Silurian and estuarine Devonian deposits, coal deposits from the Carboniferous Period and in amber. Whether the early scorpions were marine or terrestrial has been debated, though they had book lungs like modern terrestrial species.     Over 100 fossil species of scorpion have been described.  The oldest found to date is Parioscorpio venator, which lived 437 million years ago, during the Silurian. Unlike present day scorpions, but like its marine ancestors, it had compound eyes.  Gondwanascorpio from the Devonian is the earliest known terrestrial animal on the Gondwana supercontinent. 
The phylogeny of the scorpions has been debated,  but genomic analysis consistently places the Bothriuridae as sister to a clade consisting of Scorpionoidea and " Chactoidea". The scorpions diversified between the Devonian and the early Carboniferous. The main division is into the clades Buthida and Iurida. The Bothriuridae diverged starting before temperate Gondwana broke up into separate land masses. The Iuroidea and Chactoidea are both broken up and are shown as " paraphyletic" (with quotation marks). 
Thirteen families and about 1,750 described species and subspecies of scorpions are known. In addition, 111 described taxa of scorpions are extinct.  This classification is based on that of Soleglad and Fet (2003),  which replaced the older, unpublished classification of Stockwell.  Additional taxonomic changes are from papers by Soleglad et al. (2005).  
- Order Scorpiones
- Parvorder Pseudochactida Soleglad et Fet, 2003
- Parvorder Buthida Soleglad et Fet, 2003
- Parvorder Chaerilida Soleglad et Fet, 2003
- Superfamily Chactoidea Pocock, 1893
- Superfamily Iuroidea Thorell, 1876
- Superfamily Scorpionoidea Latreille, 1802
The body of a scorpion is divided into two parts ( tagmata): the cephalothorax or prosoma, and the abdomen or opisthosoma. [a] The opisthosoma is subdivided into a broad anterior portion (called the mesosoma or pre-abdomen), and a narrow tail-like posterior (called the metasoma or post-abdomen).  The scorpion's exoskeleton is thick and durable, providing good protection from predators. 
The cephalothorax comprises the carapace, eyes, chelicerae (mouth parts), pedipalps (which have chelae, commonly called claws or pincers) and four pairs of walking legs. Scorpions have two eyes on the top of the cephalothorax, and usually two to five pairs of eyes along the front corners of the cephalothorax. While unable to form sharp images, their central eyes are amongst the most light sensitive in the animal kingdom, especially in dim light, and makes it possible for nocturnal species to use starlight to navigate at night. Some species also have light receptors in their tail.  The position of the eyes on the cephalothorax depends in part on the hardness or softness of the soil upon which they spend their lives.  The chelicerae are located at the front and underneath the carapace. They are pincer-like and have three segments and sharp "teeth".  
The pedipalp is a segmented, chelate (clawed) appendage used for prey immobilization, defense and sensory purposes. The segments of the pedipalp (from closest to the body outwards) are coxa, trochanter, femur (humerus), patella, tibia (including the fixed claw and the manus) and tarsus (moveable claw). A scorpion has darkened or granular raised linear ridges, called "keels" or carinae on the pedipalp segments and on other parts of the body, which are useful taxonomically.  Unlike some other arachnids, scorpion legs have not been modified for other purposes, though they may occasionally be used for digging and the female may use them to catch emerging young. The legs are covered in proprioceptors, bristles and sensory setae.  Depending on the species, scorpion legs may also contain spines and spurs. 
The mesosoma or preabdomen is the broad part of the opisthosoma.  It consists of the anterior seven somites (segments) of the opisthosoma or abdomen, each covered dorsally by a sclerotosed plate, its tergite. Ventrally somites 3 to 7 are armoured with matching plates called sternites.  Ventrally somites 1 and 2 are more complex; the first abdominal sternite is modified into a pair of genital opercula covering the gonopore. Sternite 2 forms the basal plate bearing the pectines. Morphologically the pectines are a pair of limbs that function as sensory organs. ·
The next four somites, 3 to 6, all bear pairs of spiracles. They serve as openings for the scorpion's respiratory organs, known as book lungs. The spiracle openings may be slits, circular, elliptical or oval according to the species of scorpion.   There are thus four pairs of book lungs; each consists of some 140 to 150 thin lamellae filled with air inside a pulmonary chamber, connected on the ventral side to an atrial chamber which opens into a spiracle. Bristles hold the lamellae apart. A muscle opens the spiracle and widens the atrial chamber; dorsoventral muscles contract to compress the pulmonary chamber, forcing air out, and relax to allow the chamber to refill.  The 7th and last somite do not bear appendages or any other significant external structures. 
The metasoma ("tail") comprises five segments and the telson, which is not classified as an actual segment. The five segments are merely body rings and lack apparent sterna or terga, and become larger distally. These segments also have keels, setae and bristles which may be used for taxonomic classification. The anus is located at the distal and ventral end of the last segment, and is encircle by four anal papillae and the anal arch. 
The telson includes the vesicle, containing a symmetrical pair of venom glands. Externally it bears the curved sting, the hypodermic aculeus or venom-injecting barb. It is equipped with various sensory hairs, as the sting cannot be guided visually. Each of the venom glands has its own duct to convey its secretion internally along the aculeus from the bulb of the gland to immediately subterminal of the point of the aculeus, where each of the paired ducts has its own venom pore. 
Scorpions prefer areas where the temperatures range from 20 to 37 °C (68 to 99 °F), but may survive temperatures ranging from well below freezing to desert heat.   Scorpions of the genus Scorpiops living in high Asian mountains, bothriurid scorpions from Patagonia and small Euscorpius scorpions from Central Europe can all survive winter temperatures of about −25 °C (−13 °F). In Repetek ( Turkmenistan), seven species of scorpion (of which Pectinibuthus birulai is endemic) live in temperatures varying from −31 to 50 °C (−24 to 122 °F).  Most scorpions species are nocturnal or crepuscular, finding shelter during the day in burrows and other shelters like cracks in rocks and tree bark. 
Scorpions make be attacked by other arthropods like ants, spiders, solifugids and centipedes. Major predators include frogs, lizards, snakes, birds and mammals. When threatened, a scorpion raises its claws and tail in a defensive posture. Some species stridulate by rubbing certain hairs, the stinger or the claws. Scorpions host parasites including mites, scuttle flies, nematodes and bacteria. 
Diet and feeding
Scorpions generally prey on insects, particularly grasshoppers, crickets, termites, beetles and wasps. They also take spiders. sun spiders, woodlice and even small vertebrates including lizards, snakes and mammals. Species with large claws may prey on earthworms and mollusks. The majority of species are opportunistic and consume a variety of prey though some may be highly specialized. Prey size depends on the size of the size of the species. Several scorpion species are sit-and-wait predators, which involves them waiting for prey at or near the entrance to their burrow. Others will actively seek out them out. Scorpions detect their prey with mechanoreceptive and chemoreceptive hairs on their bodies. Scorpions capture prey with their claws. Small animals are merely killed by claws, particularly by species with large ones. Larger and more aggressive prey is given a sting, which can happen very quickly at 0.75 seconds. 
Scorpions have an unusual style of eating which is shared with other arachids. The chelicerae, which are very sharp, are used to pull small amounts of food off the prey item for digestion into a pre-oral cavity below the chelicerae and carapace. Scorpions have external digestion, and the digestive juices from the gut are egested onto the food and the digested food sucked in liquid form. Any solid indigestible matter ( exoskeleton, etc.) is trapped by setae in the pre-oral cavity and ejected by the scorpion. The sucked in food is pumped into the midgut by the pharynx were it is further digested and then the waste passes through the hindgut and out the anus. Scorpions can consume large amounts of food at one sitting. They have an efficient food storage organ and a very low metabolic rate combined with a relatively inactive lifestyle. This enables scorpions to survive long periods when deprived of food. Some are able to survive 6 to 12 months of starvation.  Scorpions excrete very little. Their waste consists mostly of insoluble nitrogenous compounds, such as xanthine, guanine and uric acid. 
Most scorpions reproduce sexually, and most species have male and female individuals; however, species in some genera, such as Hottentotta and Tityus, and the species Centruriodes gracilis, Liocheles australasiae, and Ananteris coineaui have been reported, not necessarily reliably, to reproduce through parthenogenesis, in which unfertilized eggs develop into living embryos.  Receptive females will produce pheromones which are picked up by wandering males using their pectines to comb the substrate. Male begin courtship by moving their bodies back and forth, without moving the legs, a behavior known as juddering. This appears to produce ground vibrations that are pick up by the female. 
The pair then make contact with the pedipalps and perform a "dance" called the "promenade à deux". In this "dance," the male and female move backwards and forwards while facing each other, searching for a suitable place for the male to deposit his spermatophore. The courtship ritual can involve several other behaviors such as a cheliceral kiss, in which the male and female grasp each others chelicerae, and sexual stinging, in which the male stings the female in the chelae or mesosoma in order to subdue her. When the male has location stable enough substrate, such as hard ground, agglomerated sand, rock, or tree bark, he deposits the spermatophore and then guides the female over it. This allows the spermatophore to enter her genital opercula, which triggers release of the sperm, thus fertilizing the female. A mating plug then forms in the female to prevent her from mating again before the young are born. Soon, the male and female abruptly seperative from each other.  Sexual cannibalism after mating has only been reported anecdotally in scorpions. 
Birth and development
Unlike the majority of species in the class Arachnida, which are oviparous, scorpions seem to be universally viviparous.  They are also unusual among terrestrial arthropods in the amount of care a females gives to her offspring.  Gestation can last for over a year in some species.  The size of a brood can vary by species, from three to over 100. Before giving birth, the female elevates the front of her body above the ground and positions her pedipalps and front legs under her to catch the young. The young are emerge one by one from the genital opercula, expel the embryonic membrane, if any, and are placed on the mother's back were they remain back until they have gone though at least one molt. 
The period before the first molt is called the pro-juvenile stage, and the young are unable to feed or sting and instead have suckers on their tarsi. This periods lasts 5–25 days depending on the species. The brood molt for the first time simultaneously and last 6–8 hours, which signals the beginning of the juvenile stage.  Juveniles generally resemble smaller versions of adults, having fully developed pincers, trichobothria and stingers. They are still soft and lack pigments, and thus continue to ride on their mother's back for protection. They became harder and more pigmented over the next couple days. They may leave their mother temporarily, returning when they sense potential danger. Once the tegument is fully hardened, the young can hunt prey on their own and may soon leave their mother.  A scorpion may molt six times on average before reaching maturity, which may not occur until it is 6–83 months old, depending on the species. They may live up to 25 years. 
Scorpions glow a vibrant blue-green when exposed to certain wavelengths of ultraviolet light such as that produced by a black light, due to the presence of fluorescent chemicals in the cuticle. One fluorescent component is beta-carboline. Accordingly, a hand-held UV lamp has long been a standard tool for nocturnal field surveys of these animals. Fluorescence occurs as a result of sclerotisation and increases in intensity with each successive instar.  This fluorescence may have an active role in scorpion light detection. 
Relationship with humans
In general, the venom is fast-acting, allowing for effective prey capture; however, as a general rule, scorpions kill their prey with brute force if they can, as opposed to using venom, which is also used as a defense against predators. The venom is a mixture of compounds ( neurotoxins, enzyme inhibitors, etc.), each not only causing a different effect, but possibly also targeting a specific animal. Each compound is made and stored in a pair of glandular sacs and is released in a quantity regulated by the scorpion itself. Of the more than one thousand known species of scorpions, only 25 have venom that is deadly to humans; most of those belong to the family Buthidae (including Leiurus quinquestriatus, Hottentotta spp., Centruroides spp., and Androctonus spp.).  
According to the US National Institute for Occupational Safety and Health, scorpion stings can largely be prevented by wearing long sleeves, long trousers, and leather gloves, and by shaking out clothing, bedding, bathroom towels, or shoes before using them. It recommends workers with a history of severe allergic reactions to insect bites or stings to consider carrying an epinephrine autoinjector (EpiPen), and states that they should wear a medical identification bracelet or necklace identifying their allergy. 
First aid for scorpion stings is generally symptomatic. It includes strong analgesia, either systemic ( opioids or paracetamol) or locally applied (such as a cold compress). Cases of very high blood pressure are treated with anxiety-relieving medications and medications which lower the blood pressure by widening the diameter of blood vessels.  Scorpion envenomation with high morbidity and mortality is usually due to either excessive autonomic activity and cardiovascular toxic effects or neuromuscular toxic effects. Antivenom is the specific treatment for scorpion envenomation combined with supportive measures including vasodilators in patients with cardiovascular toxic effects and benzodiazepines when neuromuscular involvement occurs. Although rare, severe hypersensitivity reactions including anaphylaxis to scorpion antivenin (SAV) are possible. 
Medical use of venom toxins
Short-chain scorpion toxins constitute the largest group of potassium (K+) channel-blocking peptides. An important physiological role of the KCNA3 channel, also known as KV1.3, is to help maintain large electrical gradients for the sustained transport of ions such as Ca2+ that controls T lymphocyte ( T cell) proliferation. Thus KV1.3 blockers could be potential immunosuppressants for the treatment of autoimmune disorders (such as rheumatoid arthritis, inflammatory bowel disease, and multiple sclerosis).  The venom of Uroplectes lineatus is clinically important in dermatology. 
Several scorpion venom toxins have been investigated for medical use. Chlorotoxin from the deathstalker scorpion (Leiurus quinquestriatus); the toxin blocks small-conductance chloride channels;   Maurotoxin from the venom of the Tunisian Scorpio maurus blocks potassium channels.  Some antimicrobial peptides in the venom of Mesobuthus eupeus; meucin-13 and meucin-18 have extensive cytolytic effects on bacteria, fungi, and yeasts,  while meucin-24 and meucin-25 selectively kill Plasmodium falciparum and inhibit the development of Plasmodium berghei, both malaria parasites, but do not harm mammalian cells. 
Fried scorpion is traditionally eaten in Shandong, China.  There, scorpions can be cooked and eaten in a variety of ways, such as roasting, frying, grilling, raw, or alive. The stingers are typically not removed, since direct and sustained heat negates the harmful effects of the venom. 
Middle Eastern culture
The scorpion is a significant animal culturally, appearing as a motif in art, especially in Islamic art in the Middle East.  A scorpion motif is often woven into Turkish kilim flat-weave carpets, for protection from their sting.  The scorpion is perceived both as an embodiment of evil and a protective force such as a dervish's powers to combat evil.  In another context, the scorpion portrays human sexuality.  Scorpions are used in folk medicine in South Asia, especially in antidotes for scorpion stings. 
One of the earliest occurrences of the scorpion in culture is its inclusion, as Scorpio, in the 12 signs of the Zodiac by Babylonian astronomers during the Chaldean period. This was then taken up by western astrology. 
Alongside serpents, scorpions are used to symbolize evil in the New Testament. In Luke 10:19 it is written, "Behold, I give unto you power to tread on serpents and scorpions, and over all the power of the enemy: and nothing shall by any means hurt you." Here, scorpions and serpents symbolize evil.  Revelation 9:3 speaks of "the power of the scorpions of the earth." 
The scorpion with its powerful sting has been used as the name or symbol of various products and brands, including Italy's Abarth racing cars.  In the Roman army, the scorpio was a torsion siege engine used to shoot a projectile.  The British Army's FV101 Scorpion was an armoured reconnaissance vehicle or light tank in service from 1972 to 1994.  It holds the Guinness world record for the fastest production tank.  A version of the Matilda II tank, fitted with a flail to clear mines, was named the Matilda Scorpion.  Several ships of the Royal Navy have been named HMS Scorpion, including an 18-gun sloop in 1803,  a turret ship in 1863,  and a destroyer in 1910. 
A hand- or forearm-balancing asana in modern yoga as exercise with the back arched and one or both legs pointing forwards over the head is called Scorpion pose.  A variety of martial arts films and video games have been entitled Scorpion King.    A Montesa scrambler motorcycle was named Scorpion. 
Scorpions have equally appeared in western artforms including film and poetry: the surrealist filmmaker Luis Buñuel made symbolic use of scorpions in his 1930 classic L'Age d'or (The Golden Age),  while Stevie Smith's last collection of poems was entitled Scorpion and other Poems. 
"Scorpion and snake fighting", Anglo-Saxon Herbal, c. 1050
Still life with scorpion and frog by Hermenegildo Bustos, 1874
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