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Scorpion
Scorpion

Scorpions are predatory arachnids of the order Scorpiones. They have eight legs[1] 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).[2]

The evolutionary history of scorpions goes back to the Silurian period 430 million years ago. They have adapted to a wide range of environmental conditions, and they can now be found on all continents except Antarctica. Scorpions number about 1,750 described species,[3] with 13 extant (living) families recognised to date. The taxonomy has undergone changes and is likely to change further, as genetic studies are bringing forth new information.

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.[4] Only about 25 species are known to have venom capable of killing a human.[5] In some parts of the world with highly venomous species, human fatalities regularly occur, primarily in areas with limited access to medical treatment.[4]

Etymology


The word "scorpion" is thought to have originated in Middle English between 1175 and 1225 AD from Old French scorpion,[6] or from Italian scorpione, both derived from the Latin scorpius,[7] which is the romanization of the Greek word σκορπίοςskorpíos.[8]

Geographical distribution


Scorpions are found on all major land masses except Antarctica and New Zealand.

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.[5] [12] As regards 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.[13]

Classification


Thirteen families and about 1,750 described species and subspecies of scorpions are known.

This classification is based on that of Soleglad and Fet (2003),[15] which replaced the older, unpublished classification of Stockwell.[16] Additional taxonomic changes are from papers by Soleglad et al. (2005).[17][18]

This classification covers extant taxa to the rank of family:

Fossil record


Scorpion remains have been found in many fossil records, including marine Silurian and estuarine Devonian deposits, coal deposits from the Carboniferous Period and in amber. The oldest known scorpions lived around 430 million years ago in the Silurian period. Though once believed to have lived on the bottom of shallow tropical seas,[19] early scorpions are now believed to have been terrestrial and to have washed into marine settings together with plant matter. These first scorpions were believed to have had gills instead of the present forms' book lungs, though this has subsequently been refuted.[20][21][22] The oldest Gondwanan scorpions (Gondwanascorpio) comprise the earliest known terrestrial animals from Gondwana.[23] Currently, 111 fossil species of scorpion are known.[14] Unusually for arachnids, there are more species of Palaeozoic scorpion than Mesozoic or Cenozoic ones.

Ancestral scorpions had compound eyes, but as they adapted to a nocturnal lifestyle, they became simplified.[24]

The eurypterids, commonly called "sea scorpions", were aquatic creatures that lived during the Palaeozoic era that share several physical traits with scorpions and may be closely related to them. Various species of Eurypterida could grow to be anywhere from 10 centimetres (3.9 in) to 2.5 metres (8.2 ft) in length.[25] However, they exhibit anatomical differences marking them off as a group distinct from their Carboniferous and Recent relatives. Despite this, they are commonly referred to as "sea scorpions".[26] Their legs are thought to have been short, thick, tapering and to have ended in a single strong claw. It appears that they were well-adapted for maintaining a secure hold upon rocks or seaweed against the wash of waves, like the legs of a shore crab. Cladistic analyses have supported the idea that the eurypterids are a distinct group from the scorpions.[27]

Morphology


The body of a scorpion is divided into two parts (tagmata): the head (cephalothorax) and the abdomen (opisthosoma), which is subdivided into a broad anterior (mesosoma), or preabdomen, and a narrow tail-like posterior (metasoma), or postabdomen.[5]

The cephalothorax, also called the prosoma, comprises the carapace, eyes, chelicerae (mouth parts), pedipalps (the pedipalps of scorpions have chelae, commonly called claws or pincers) 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 star light to navigate at night. Some species also have light receptions in their tail.[28] 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.[29]

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).[30] 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.[5]

The mesosoma is the broad part of the opisthosoma.

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.[31]

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.[5] [32]

The 7th and last somite do not bear appendages or any other significant external structures.[33]

The 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 (anterior) 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.[34]

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.[35]

On rare occasions, scorpions are born with two metasomata.

Fluorescence


Scorpions are also known to 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 now known to be beta-carboline.[37] 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.[37] This fluorescence may have an active role in scorpion light detection.[38]

Biology


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.[39][40] 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).[41]

They 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 such as the grasshopper mouse, opossums, and larger mammals including mongooses and the honey badger.[42]

Scorpions are opportunistic predators of small arthropods, although the larger kinds have been known to kill small lizards and snakes.

Scorpions can consume huge amounts of food at one sitting.

Most scorpions reproduce sexually, and most species have male and female individuals; however, some species, such as Hottentotta hottentotta, Hottentotta caboverdensis, Liocheles australasiae, Tityus columbianus, Tityus metuendus, Tityus serrulatus, Tityus stigmurus, Tityus trivittatus and Tityus urugayensis, reproduce through parthenogenesis, a process in which unfertilized eggs develop into living embryos. Parthenogenic reproduction starts following the scorpion's final molt to maturity and continues thereafter.

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.

When the male has identified a suitable location, he deposits the spermatophore and then guides the female over it.

Once the mating is complete, the male will generally retreat quickly, for unknown reasons; sexual cannibalism is infrequent with scorpions.

Unlike the majority of species in the class Arachnida, which are oviparous, scorpions seem to be universally viviparous.[44] 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 (e.g. Pandinus spp.), 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.[45]

The young generally resemble their parents.

Relationship with humans


Although scorpions are usually not found in large numbers in densely populated urban areas, they do regularly occur in and near human habitation in all tropical parts of the world.

All known scorpion species possess venom and use it primarily to kill or paralyze their prey so that it can be eaten.

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.

According to the United States National Institute for Occupational Safety and Health, these steps should be taken to prevent scorpion stings:[49]

  • Wear long sleeves and trousers.
  • Wear leather gloves.
  • Shake out clothing, bedding, bathroom towels, or shoes before using them.
  • Workers with a history of severe allergic reactions to insect bites or stings should consider carrying an epinephrine autoinjector (EpiPen) and should wear a medical identification bracelet or necklace stating 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.[50] 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.[51]

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).[52]

The venom of Uroplectes lineatus is clinically important in dermatology.[53]

Toxins being investigated include the following:

Scorpions for use in the pharmaceutical industry are collected from the wild in Pakistan. Farmers in the Thatta District are paid about US$100 for each 40-gram scorpion, and 60-gram specimens are reported to fetch at least US$50,000.[59] The trade is reported to be illegal but thriving.[60]

The venom is one of the most valuable liquids by volume on earth and it costs $39 million to produce a gallon of the toxin.[61]

Fried scorpion is a traditional dish from Shandong, China.[62]

  • One of earliest occurrences of the scorpion in culture is its inclusion, as Scorpio, in the 12 signs of the series of constellations known as the Zodiac by Babylonian astronomers during the Chaldean period.[5]
  • In South Africa and South Asia, the scorpion is a significant animal culturally, appearing as a motif in art, especially in Islamic art in the Middle East.[63] A scorpion motif is often woven into Turkish kilim flat-weave carpets, for protection from their sting.[64] The scorpion is perceived both as an embodiment of evil and a protective force that counters evil, such as a dervish's powers to combat evil.[63] In another context, the scorpion portrays human sexuality.[63] Scorpions are used in folk medicine in South Asia, especially in antidotes for scorpion stings.[63]
  • In ancient Egypt, the goddess Serket was often depicted as a scorpion, one of several goddesses who protected the Pharaoh.
  • A horse named Nama, with a scorpion drawn on his body, is depicted on a pitcher of the ancient Roman city of Tamuda, near Tetouan (Morocco), as a mark of the stable of Tingitanus.[65]
  • Surrealist filmmaker Luis Buñuel makes notable symbolic use of scorpions in his 1930 classic L'Age d'or (The Golden Age).[66]
  • 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.[67] Revelation 9:3 speaks of "the power of the scorpions of the earth."[68]
  • The last collection of poems by Stevie Smith was entitled Scorpion and other Poems.[69]

See also


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