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. to 23 cm / 9 in..
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 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.
EtymologyThe word ":wikt:scorpion|scorpion" is thought to have originated in Middle English between 1175 and 1225 AD from Old French ', or from Italian ', both derived from the Latin , which is the romanization of the Greek word :wikt:σκορπίος – skorpíos.
Geographical distributionScorpions are found on all major land masses except Antarctica and New Zealand. Scorpions did not occur naturally in Great Britain, Ireland, Japan, South Korea, and some of the islands in Oceania, but now have been accidentally introduced in some of these places by human trade and commerce. The greatest diversity of scorpions in the Northern Hemisphere is to be found in regions between the latitudes 23 and 38°N. Above these latitudes, the diversity decreases with the northernmost natural occurrence of scorpions being the northern scorpion Paruroctonus boreus at Medicine Hat, Alberta, Canada 50°N. Five colonies of scorpions have established themselves in Sheerness on the Isle of Sheppey in the United Kingdom. This small population has been resident since the 1860s, having probably arrived with imported fruit from Africa. This scorpion species is small and completely harmless to humans. At just over 51°N, this marks the northernmost limit where scorpions live in the wild.
Today, scorpions are found in virtually every terrestrial habitat including: high-elevation mountains, caves, and intertidal zones, with the exception of boreal ecosystems such as: the tundra, high-altitude taiga, and the permanently snow-clad tops of some mountains. 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.
Fossil recordScorpion 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. It was not yet fully terrestrial. 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.
PhylogenyThe 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".
TaxonomyThirteen 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, which replaced the older, unpublished classification of Stockwell. Additional taxonomic changes are from papers by Soleglad et al..
The extant taxa to the rank of family are:
; Order Scorpiones
- Parvorder Pseudochactida Soleglad et Fet, 2003
- * Superfamily Pseudochactoidea Gromov, 1998
- ** Family Pseudochactidae Gromov, 1998
- Parvorder Buthida Soleglad et Fet, 2003
- * Superfamily Buthoidea C. L. Koch, 1837
- ** Family Buthidae C. L. Koch, 1837
- ** Family Microcharmidae Lourenço, 1996, 2019
- Parvorder Chaerilida Soleglad et Fet, 2003
- * Superfamily Chaeriloidea Pocock, 1893
- ** Family Chaerilidae Pocock, 1893
- Parvorder Iurida Soleglad et Fet, 2003
- * Superfamily Chactoidea Pocock, 1893
- ** Family Chactidae Pocock, 1893
- ** Family Euscorpiidae Laurie, 1896
- ** Family Superstitioniidae Stahnke, 1940
- ** Family Vaejovidae Thorell, 1876
- * Superfamily Iuroidea Thorell, 1876
- ** Family Caraboctonidae Kraepelin, 1905
- ** Family Iuridae Thorell, 1876
- * Superfamily Scorpionoidea Latreille, 1802
- ** Family Bothriuridae Simon, 1880
- ** Family Hemiscorpiidae Pocock, 1893
- ** Family Scorpionidae Latreille, 1802
CephalothoraxThe cephalothorax comprises the carapace, eyes, chelicerae, pedipalps and four pairs of walking legs. The scorpion's exoskeleton is thick and durable, providing good protection from predators. 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 pedipalp is a segmented, chelate appendage used for prey immobilization, defense and sensory purposes. The segments of the pedipalp are coxa, trochanter, femur, patella, tibia and tarsus. 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.
MesosomaThe mesosoma is the broad part of the opisthosoma. Sometimes it is loosely called the abdomen. It consists of the anterior seven somites of the opisthosoma, 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 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.
MetasomaThe metasoma is commonly known as the scorpion's "tail", though this is in some ways misleading because unlike most so-called tails it is not an appendage or limb. It is in fact part of the opisthosoma. It comprises five segments, of which the fifth segment bears the telson. In many species, it superficially seems as though the metasoma has four segments only, because their first metasomal segment gives the impression of being the posterior segment of the mesosoma. The fifth segment of the metasoma is the caudal segment of the opisthosoma, and accordingly bears the anus. The scorpion's telson is the part commonly called the stinger; it is attached to the end of the fifth segment just dorsad from the anus, but as the distal end of the tail at rest normally is carried upside down with the sting pointing forward, the anus usually is above the base of the telson and facing upwards.
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.
BiologyScorpions prefer areas where the temperatures range from, 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. In Repetek, seven species of scorpion live in temperatures varying from.
Scorpions are nocturnal and fossorial, finding shelter during the day in the relative cool of underground holes or undersides of rocks, and emerging at night to hunt and feed. Scorpions exhibit photophobic behavior, primarily to evade detection by predators such as birds, lizards, rodents like the grasshopper mouse, opossums, and larger mammals including mongooses and the honey badger.
Scorpions are opportunistic predators of small arthropods, although the larger kinds have been known to kill small lizards and snakes. The large pincers are studded with highly sensitive tactile hair, and the moment an insect touches these, they use their chelae to catch the prey. Depending on the toxicity of their venom and size of their claws, they then either crush the prey or inject it with neurotoxic venom. This kills or paralyzes the prey, so the scorpion can eat it. Scorpions have an unusual style of eating using chelicerae, small clawlike structures that protrude from the mouth that are unique to the Chelicerata among arthropods. 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 can ingest food only in a liquid form; they have external digestion. The digestive juices from the gut are egested onto the food and the digested food sucked in liquid form. Any solid indigestible matter is trapped by setae in the pre-oral cavity and ejected by the scorpion.
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.
ReproductionMost 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.
Sexual reproduction is accomplished by the transfer of a spermatophore from the male to the female. Scorpions possess a complex courtship and mating ritual to effect this transfer. Mating starts with the male and female locating and identifying each other using a mixture of pheromones and vibrational communication. Once they have satisfied the other that they are of opposite sex and of the correct species, mating can commence.
The courtship starts with the male grasping the female's pedipalps with his own. The pair then perform a "dance" called the "promenade à deux". In this "dance," the male leads the female around searching for a suitable place to deposit his spermatophore. The courtship ritual can involve several other behaviors such as juddering and a cheliceral kiss, in which the male's chelicerae – pincers – grasp the female's in a smaller, more intimate version of the male's grasping the female's pedipalps, and in some cases injecting a small amount of his venom into her pedipalp or on the edge of her cephalothorax.
When the male has identified a suitable location, 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. The mating process can take from 1 to 25+ hours, and depends on the ability of the male to find a suitable place to deposit his spermatophore. If mating continues too long, the female may lose interest, ending the process.
Sexual cannibalism after mating has only been reported anecdotally in scorpions.
Birth and developmentUnlike the majority of species in the class Arachnida, which are oviparous, scorpions seem to be universally viviparous. The young are born one by one, expel the embryonic membrane, if any, and the brood is carried about on its mother's back until the young have undergone at least one molt. Before the first molt, scorplings cannot survive naturally without the mother, since they depend on her for protection and to regulate their moisture levels. Especially in species that display more advanced sociability, the young/mother association can continue for an extended period of time. The size of the litter depends on the species and environmental factors, and can range from 2 to more than 100 scorplings. The average litter however, consists of around eight scorplings.
The young generally resemble their parents. Growth is accomplished by periodic shedding of the exoskeleton. A scorpion's developmental progress is measured in instars. Scorpions typically require between five and seven molts to reach maturity. Molting commences with a split in the old exoskeleton just below the edge of the carapace. The scorpion then emerges from this split. The pedipalps and legs are first removed from the old exoskeleton, followed eventually by the metasoma. When it emerges, the scorpion's new exoskeleton is soft, making the scorpion highly vulnerable to attack. The scorpion must constantly stretch while the new exoskeleton hardens to ensure that it can move when the hardening is complete. The process of hardening is called sclerotisation. The new exoskeleton does not fluoresce. As sclerotisation occurs, the fluorescence gradually returns.
FluorescenceScorpions 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
StingsAll known scorpion species possess venom and use it primarily to kill or paralyze their prey so that it can be eaten. The venom consists of a collection of peptides.
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, 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.
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, 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 or locally applied. 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 are possible.
Medical use of venom toxinsShort-chain scorpion toxins constitute the largest group of potassium 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 proliferation. Thus KV1.3 blockers could be potential immunosuppressants for the treatment of autoimmune disorders.
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 ; 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.
ConsumptionFried 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 cultureThe 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.
In ancient Egypt, the goddess Serket was often depicted as a scorpion, one of several goddesses who protected the Pharaoh.
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."
Western cultureThe 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, while Stevie Smith's last collection of poems was entitled Scorpion and other Poems.