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 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.

Classification

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This classification is based on that of Soleglad and Fet (2003), which replaced the older, unpublished classification of Stockwell.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).

Systematics

This classification covers extant taxa to the rank of family:

Order Scorpiones

• Infraorder Orthosterni Pocock, 1911
  • 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 (thick-tailed scorpions)
      • Family Microcharmidae Lourenço, 1996
  • 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 (hairy scorpions)
      • Family Iuridae Thorell, 1876
    • Superfamily Scorpionoidea Latreille, 1802
      • Family Bothriuridae Simon, 1880
      • Family Hemiscorpiidae Pocock, 1893 (= Ischnuridae, =Liochelidae) (rock scorpions, creeping scorpions, or tree scorpions)
      • Family Scorpionidae Latreille, 1802 (burrowing scorpions or pale-legged scorpions)

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, 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. The oldest Gondwanan scorpions (Gondwanascorpio) comprise the earliest known terrestrial animals from Gondwana. Currently, 111 fossil species of scorpion are known. 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.

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. 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". 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.

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.

Cephalothorax

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. 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 (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.

Mesosoma

The mesosoma is the broad part of the opisthosoma. Sometimes it is loosely called the abdomen. It consists of the anterior seven somites (segments) 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 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.

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

Metasoma

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.

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.

On rare occasions, scorpions are born with two metasomata. Two-tailed scorpions are no more than examples of adventitious ontogenic abnormality. Whether there ever is a genetic component to the condition is uncertain, but such evidence as is available from offspring is negative so far as no two-tailed scorpions have been observed among the rarely-observed progeny of multiple-tailed scorpion specimens.

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. 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.

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. 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).

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.

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 (pincers) to catch the prey. Depending on the toxicity of their venom and size of their claws, they will then either crush the prey or inject it with neurotoxic venom. This will kill or paralyze the prey so the scorpion can eat it. Scorpions have an unusual style of eating using chelicerae, small claw-like 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 (fur, exoskeleton, etc.) is trapped by setae in the pre-oral cavity and ejected by the scorpion.

Scorpions can consume huge amounts of food at one sitting. They have a very 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.

Reproduction

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. 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, probably as a means of pacifying the female.

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.

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

Birth and development

Unlike 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 (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.

The young generally resemble their parents. Growth is accomplished by periodic shedding of the exoskeleton (ecdysis). A scorpion's developmental progress is measured in instars (how many molts it has undergone). 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 (at the front of the prosoma). 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.

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. The lack of predators, readily available shelter, and abundance of insect prey such as crickets, cockroaches, silverfishes, and earwigs have caused scorpions to thrive in industrial and residential areas. In Brazil, the number of people stung by scorpions increased from 12,000 in 2000 to 140,000 in 2018.

Sting and venom

All 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 (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 1,000+ 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.).

Prevention

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

• 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.

Treatment

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

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 K_V1.3, is to help maintain large electrical gradients for the sustained transport of ions such as Ca²⁺ that controls T lymphocyte (T cell) proliferation. Thus K_V1.3 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.

Toxins being investigated include the following:

• Chlorotoxin is a 36-amino acid peptide found in the venom of the deathstalker scorpion (Leiurus quinquestriatus) that blocks small-conductance chloride channels. The fact that chlorotoxin binds preferentially to glioma cells has allowed the development of new methods, that still are under investigation, for the treatment and diagnosis of several types of cancer.
• Maurotoxin from the venom of the Tunisian Scorpio maurus
• A number of antimicrobial peptides have also been found in the venom of Mesobuthus eupeus. Meucin-13 and meucin-18 exhibited extensive cytolytic effects on bacteria, fungi, and yeasts. Furthermore, meucin-24 and meucin-25, first identified from genetic sequences expressed in their venom gland, were shown to selectively kill Plasmodium falciparum and inhibit the development of Plasmodium berghei, both malaria parasites, but do not harm mammalian cells. These two venom-derived proteins are therefore attractive candidates for the development of anti-malarial drugs.

Production

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. The trade is reported to be illegal but thriving.

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.

Consumption

Fried scorpion is a traditional dish from Shandong, China.

In culture

• 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.
• 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. 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 that counters evil, 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.
• 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.
• Surrealist filmmaker Luis Buñuel makes notable symbolic use of scorpions in his 1930 classic L'Age d'or (The Golden Age).
• 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 last collection of poems by Stevie Smith was entitled Scorpion and other Poems.

See also

• Palaeophonus, a Devonian scorpion
• Paraisobuthus, a Carboniferous scorpion
• List of scorpions of Australia

References

External links

• "Diseases and Conditions - Scorpion stings". Mayo Clinic.

• Holland, Ben (2008). "Scorpion Facts for Researchers and Kids".
• Scorpion anatomy
• "Scorpions". DesertUSA.com and Digital West Media, Inc.
• Rehak, Ondrej. "Photogallery - 36 species of scorpions".
• Britt, Robert Roy (June 27, 2006). "Scorpion Venom Tested as Brain Cancer Treatment". LiveScience. Imaginova.
• "Pet Scorpion Information and facts | Scorpion Picture Guide".
• Scorpions from the Chihuahuan Desert Region of Mexico and the United States
• CDC - Insects and Scorpions - NIOSH Workplace Safety and Health Topic
• Scorpions distribution maps