Scorpion

Scorpion
Fossil range: Silurian–Recent
Asian forest scorpion in Khao Yai National Park, Thailand
Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Chelicerata
Class: Arachnida
Subclass: Dromopoda
Order: Scorpiones
C. L. Koch, 1837
Superfamilies

Buthoidea
Chaeriloidea
Chactoidea
Iuroidea
Scorpionoidea
See classification for families.

Scorpions are predatory arthropod animals of the order Scorpiones within the class Arachnida. They have eight legs and are easily recognised by the pair of grasping claws and the narrow, segmented tail, carried in a characteristic forward curve over the back, ending with a venomous stinger. Though the scorpion has a fearsome reputation as venomous, only 25 species have venom capable of killing a human being. While a variety of physiological, morphological, biochemical and ecological adaptations have allowed the scorpions to flourish on earth from the Silurian period (443 to 416 million years ago) onwards, the basic shape of the scorpion has not changed significantly.[1]:1

Scorpions are found widely distributed south of about 49° N, except Antarctica, in a variety of terrestrial habitats except the high latitude tundra. They have been introduced by humans to England and New Zealand. Scorpions number about 1400 described species and subspecies, with thirteen extant families recognised to date. The taxonomy has undergone changes, and is likely to change further, as a number of genetic studies are bringing forth new information.

Contents

Etymology

The word scorpion is thought to have originated in Middle English between 1175 and 1225 AD from Old French skorpiō,[2] itself derived from the Latin word scorpion,[3] which in turn has its roots in the Greek word σκορπιός – skorpios.[4]

Geographical distribution

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 have been accidentally introduced in these places by human trade and commerce.[1]:249 The greatest diversity of scorpions in the Northern Hemisphere is to be found in the subtropical areas lying between latitudes 23° N and 38° N. Above these latitudes, the diversity decreases and no scorpions can be found above 49° N.[1]:251

Scorpions are found in virtually every habitat, including high elevation mountain-tops, 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.[1]:251-252[5] As regards microhabitats, scorpions may be ground-dwelling, tree-living, lithophilic (rock-loving) or psammophilic (sand-loving); some species such as Vaejovis janssi are versatile and found in every type of habitat in Baja California while others occupy specialised niches such as Euscorpius carpathicus which occupies the littoral zone of the shore.[6]

Five colonies of scorpions (Euscorpius flavicaudis) have established themselves in Sheerness on the Isle of Sheppey in the United Kingdom. This small colony has been resident since the 1860s, having probably arrived with imported fruit from Africa, but the number of colonies could be lower now because of the destruction of their habitats. This scorpion species is small and completely harmless to humans. This marks the northernmost limit in the world where scorpions live in the wild.[7][8]

Classification

There are thirteen families and about 1,400 described species and subspecies of scorpions. In addition, there are 111 described taxa of extinct scorpions.[9]

This classification is based on that of Soleglad & Fet (2003),[10] which replaced the older, unpublished classification of Stockwell.[11] Additional taxonomic changes are from papers by Soleglad et al. (2005).[12][13]

Systematics

The following classification covers extant taxa to the rank of family.

Order Scorpiones

Fossil record

Scorpions have been found in many fossil records, including marine Silurian deposits, coal deposits from the Carboniferous Period and in amber. The oldest known scorpions lived around 430 million years ago in the Silurian period, on the bottom of shallow tropical seas.[14] These first scorpions had gills instead of the present forms' book lungs. Currently, 111 fossil species of scorpion are known.[9] Unusually for arachnids, there are more species of Palaeozoic scorpion than Mesozoic or Cenozoic ones.

The eurypterids, marine creatures which lived during the Paleozoic era, share several physical traits with scorpions and may be closely related to them. Various species of Eurypterida could grow to be anywhere from 10 to 250 centimetres (3.9 to 98 in) 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".[15] 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.

Biology

Anatomy

Scorpion anatomy:
1 = Cephalothorax or Prosoma;
2 = Abdomen or Mesosoma;
3 = Tail or Metasoma;
4 = Claws or Pedipalps
5 = Legs;
6 = Mouth parts or Chelicerae;
7 = pincers or Chelae;
8 = Moveable claw or Manus;
9 = Fixed claw or Tarsus;
10 = Sting or Telson;
11 = Anus.
Barb of an Arizona bark scorpion

The body of a scorpion is divided into two parts (tagmata): the cephalothorax (also called the prosoma) and the abdomen (opisthosoma). The abdomen consists of the mesosoma and the metasoma.[1]:10

Cephalothorax

The cephalothorax, also called the prosoma, is the scorpion's “head”, comprising the carapace, eyes, chelicerae (mouth parts), pedipalps (commonly called claws, pincers or chelae) 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 head, and usually two to five pairs of eyes along the front corners of the head. The position of the eyes on the head depends in part on the hardness or softness of the soil upon which they spend their lives.[16]

The pedipalp is a segmented, chelate (clawed) appendage used to immobilise the prey, defense and for sensory purposes. The segments of the pedipalp (from closest to the body outwards) are coxa, trochanter, femur (humerus), patella, tibia (manus, hand or movable claw) and tarsus (fixed 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.[1]:12

Mesosoma

The abdomen consists of seven segments (somites), each covered dorsally by a sclerotosed plate (tergum) and also ventrally for segments 3 to 7. The first abdominal segment bears a pair of genital opercula which cover the gonopore. Segment 2 consists of the basal plate with the pectines. Each of the mesosomal segments 3 to 7 have a pair of spiracles which are the openings for the scorpion's respiratory organs, known as book lungs. The spiracle openings may be slits, circular, elliptical, or oval.[1]:13-15

Metasoma

The metasoma, the scorpion's tail, comprises six segments (the first tail segment looks like a last mesosoman segment), the last containing the scorpion's anus and bearing the telson (the sting). The telson, in turn, consists of the vesicle, which holds a pair of venom glands, and the hypodermic aculeus, the venom-injecting barb.

On rare occasions, scorpions can be born with two metasomata (tails). Two-tailed scorpions are not a different species, merely a genetic abnormality.[17]

Fluorescence in ultraviolet light

A scorpion under a black light. In normal lighting this scorpion appears black.

Scorpions are also known to glow when exposed to certain wavelengths of ultraviolet light such as that produced by a blacklight, due to the presence of fluorescent chemicals in the cuticle. One fluorescent component is now known to be beta-Carboline.[18] A hand-held UV lamp has long been a standard tool for nocturnal field surveys of these animals. Fluorescence occurs as a result of sclerotization and increases in intensity with each successive instar.[18]

Life and habits

Scorpions have quite variable lifespans and the actual lifespan of most species is not known. The age range appears to be approximately 4–25 years (25 years being the maximum reported life span in the species Hadrurus arizonensis). Lifespan of Hadogenes species in the wild is estimated at 25–30 years.

Scorpions prefer to live in areas where the temperatures range from 20 °C to 37 °C (68 °F to 99 °F), but may survive from freezing temperatures to the desert heat.[19][20] 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) there live seven species of scorpions (of which Pectinibuthus birulai is endemic) in temperatures which vary from .[21]

They are nocturnal and fossorial, finding shelter during the day in the relative cool of underground holes or undersides of rocks and coming out at night to hunt and feed. Scorpions exhibit photophobic behavior, primarily to evade detection by their predators such as birds, centipedes, lizards, mice, possums, and rats.[22]

Scorpions are opportunistic predators of small arthropods and insects, although the larger kinds have been known to kill small lizards and mice. The large pincers are studded with highly sensitive tactile hairs, 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 a relatively unique 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 only digest food 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 which is ejected by the scorpion.[1]:296-297

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.[1]:297-298 Scorpions excrete very little, their waste consists mostly of insoluble nitrogenous waste such as xanthine, guanine and uric acid.[6]

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 unfertilised eggs develop into living embryos. Parthenogenic reproduction starts following the scorpion's final moult 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 each 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 reality this is the male leading the female around searching for a suitable place to deposit his spermatophore. The courtship ritual can involve several other behaviours such as juddering and a cheliceral kiss, in which the male's chelicerae – clawlike mouthparts – 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,[23] 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 goes on for too long, the female may eventually lose interest, breaking off the process.

Once the mating is complete, the male and female will separate. The male will generally retreat quickly, most likely to avoid being cannibalised by the female, although sexual cannibalism is infrequent with scorpions.

Birth and development

Compsobuthus werneri female with young

Unlike the majority of arachnid species, scorpions are viviparous. The young are born one by one, 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 which 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 two to over a hundred scorplings. The average litter however, consists of around 8 scorplings.[24]

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 moults it has undergone). Scorpions typically require between five and seven moults to reach maturity. Moulting is effected by means of a split in the old exoskeleton which takes place 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 sclerotization. The new exoskeleton does not fluoresce; as sclerotization occurs, the fluorescence gradually returns.

Relationship with humans

Scorpion 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; in general it is fast-acting, allowing for effective prey capture. It 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 1000+ known species of scorpion, only 25 have venom that is dangerous to humans; all belong to the family Buthidae.[6][25]

Medical use

The key ingredient of the venom is a scorpion toxin protein.

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).[26]

The venom of Uroplectes lineatus is clinically important in dermatology.[27]

The deathstalker has powerful venom.

Toxins being investigated include:

In culture

One of earliest occurrences of the scorpion in culture is its inclusion, as Scorpio, in the twelve signs of the series of constellations known as the Zodiac by Babylonian astronomers during the Chaldean period.[1]:462

In North Africa and South Asia, the scorpion is a significant animal culturally which appears as a motif in art, especially in Islamic art in the Middle East. It is perceived both as an embodiment of evil as well as a protective force which 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 bites.[30]

In ancient Egypt the goddess Serket was often depicted as a scorpion, one of several goddesses who protected the Pharaoh.

References

  1. ↑ 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 Polis, Gary A. (1990). The Biology of Scorpions. Stanford University Press. pp. 587. ISBN 9780804712491. http://books.google.com/?id=6OqeAAAAIAAJ. Retrieved 2010-04-03. 
  2. ↑ "scorpion". (n.d.) The American Heritage® Dictionary of the English Language, Fourth Edition. (2003). Retrieved April 14, 2010 from http://www.thefreedictionary.com/scorpion.
  3. ↑ "scorpion". Dictionary.com. Dictionary.com Unabridged. Random House, Inc. http://dictionary.reference.com/browse/scorpion (accessed: April 14, 2010).
  4. ↑ Skorpios, Henry George Liddell, Robert Scott, A Greek-English Lexicon, at Perseus.
  5. ↑ Huber, Bernhard A.; Sinclair, Bradley J. & Lampe, K.-H. (2005). African biodiversity: molecules, organisms, ecosystems. Springer. p. 26. ISBN 9780387243153. http://books.google.com/?id=6Yr_OJsU_aYC. Retrieved 2010-04-14. 
  6. ↑ 6.0 6.1 6.2 Gordon Ramel. "The Earthlife Web: The Scorpions". The Earthlife Web. http://www.earthlife.net/chelicerata/scorpionidae.html. Retrieved 2010-04-08. 
  7. ↑ Benton, T. G. (1991). "The life history of Euscorpius flavicaudis (Scorpiones, Chactidae)". Journal of Arachnology 19: 105–110. http://www.americanarachnology.org/JoA_free/JoA_v19_n2%20/JoA_v19_p105.pdf. Retrieved 2008-06-13. 
  8. ↑ Rein, Jan Ove (2000). "Euscorpius flavicaudis". The Scorpion Files. Norwegian University of Science and Technology. http://www.ub.ntnu.no/scorpion-files/e_flavicaudis.htm. Retrieved 2008-06-13. 
  9. ↑ 9.0 9.1 Dunlop, Jason A.; Penney, David; Tetlie, O. Erik & Anderson, Lyall I. (2008). "How many species of fossil arachnids are there". Journal of Arachnology (BioOne) 36 (2): 262–272. doi:10.1636/CH07-89.1. http://www.bioone.org/doi/abs/10.1636/CH07-89.1. Retrieved 2010-04-07. 
  10. ↑ Soleglad, Michael E.; Victor Fet (2003). "High-level systematics and phylogeny of the extant scorpions (Scorpiones: Orthosterni)" (multiple parts). Euscorpius (Marshall University) 11: 1–175. http://www.science.marshall.edu/fet/euscorpius/pubs.htm. Retrieved 2008-06-13. 
  11. ↑ Scott A. Stockwell, 1989. Revision of the Phylogeny and Higher Classification of Scorpions (Chelicerata). Ph.D. Dissertation, University of California, Berkeley
  12. ↑ Soleglad, Michael E.; Victor Fet & F. Kovařík (2005). "The systematic position of the scorpion genera Heteroscorpion Birula, 1903 and Urodacus Peters, 1861 (Scorpiones: Scorpionoidea)". Euscorpius (Marshall University) 20: 1–38. http://www.science.marshall.edu/fet/euscorpius/p2005_20.pdf. Retrieved 2008-06-13. 
  13. ↑ Fet, V.; Soleglad, E. (2005). "Contributions to scorpion systematics. I. On recent changes in high-level taxonomy.". Euscorpius (Marshall University) (31): 1–13. ISSN 1536-9307. http://www.science.marshall.edu/fet/euscorpius/p2005_31.pdf. Retrieved 2010-04-07. 
  14. ↑ Andrew Jeram (June 16, 1990). "When scorpions ruled the world". New Scientist. http://www.newscientist.com/article/mg12617214.200-when-scorpions-ruled-the-world-scorpions-took-the-big-step-onto-solid-ground-about-300-million-years-ago-scottish-fossils-reveal-how-they-evolved-to-leave-the-seas-and-become-the-first-predators-on-land.html. 
  15. ↑ Waggoner, Ben. "Eurypterida". Regents of the University of California. http://www.ucmp.berkeley.edu/arthropoda/chelicerata/eurypterida.html. Retrieved 2008-06-13. 
  16. ↑ http://insects.tamu.edu/extension/bulletins/l-1678.html
  17. ↑ Prchal, Steve. "Pepe the Two Tailed Scorpion". Sonoran Arthropod Studies Institute. http://www.sasionline.org/pepe.htm. Retrieved 2008-06-13. 
  18. ↑ 18.0 18.1 Stachel, Shawn J; Scott A Stockwell and David L Van Vranken (August 1999). "The fluorescence of scorpions and cataractogenesis". Chemistry & Biology (Cell Press) 6: 531–539. doi:10.1016/S1074-5521(99)80085-4. http://www.chembiol.com/content/article/abstract?uid=PIIS1074552199800854. Retrieved 2008-06-17. 
  19. ↑ Hadley, Neil F. (1970). "Water Relations of the Desert Scorpion, Hadrurus Arizonensis". Journal of Experimental Biology 53 (3): 547–558. PMID 5487163. http://jeb.biologists.org/cgi/reprint/53/3/547.pdf. Retrieved 2008-06-13. 
  20. ↑ Hoshino, K.; A. T. V. Moura & H. M. G. De Paula (2006). "Selection of Environmental Temperature by the Yellow Scorpion Tityus serrulatus Lutz & Mello, 1922 (Scorpiones, Buthidae)". Journal of Venomous Animals and Toxins including Tropical Diseases 12 (1): 59–66. doi:10.1590/S1678-91992006000100005. http://www.scielo.br/pdf/jvatitd/v12n1/28301.pdf. Retrieved 2008-06-13. 
  21. ↑ (Kovařík, František; Štíři (Scorpions), Jihlava 1998, p. 19
  22. ↑ "Scorpions". Australian Museum. http://www.amonline.net.au/factsheets/scorpions.htm. Retrieved 2008-06-13. 
  23. ↑ Hickman Jr., Cleveland P.; Larry S. Roberts, Allan Larson, Helen I'Anson, David Eisenhour (2005-02-01). Integrated Principles of Zoology (13 ed.). McGraw-Hill Science/Engineering/Math. pp. 380. ISBN 978-0073101743. 
  24. ↑ Lourenco, W. R. (2000). "Reproduction in scorpions, with special reference to parthenogenesis". European Arachnology: 71–85. http://www.european-arachnology.org/proceedings/19th/Lourenco.PDF. 
  25. ↑ "ThinkQuest: Poisonous Animals: Scorpions". http://library.thinkquest.org/C007974/2_4sco.htm. Retrieved 2009-12-16. 
  26. ↑ Chandy KG, Wulff H, Beeton C, Pennington M, Gutman GA, Cahalan MD (May 2004). "K+ channels as targets for specific immunomodulation". Trends in Pharmacological Sciences 25 (5): 280–289. doi:10.1016/j.tips.2004.03.010. PMID 15120495. PMC 2749963. http://www.pubmedcentral.nih.gov/articlerender.fcgi?tool=pubmed&pubmedid=15120495. 
  27. ↑ Rapini, Ronald P.; Bolognia, Jean L.; Jorizzo, Joseph L. (2007). Dermatology: 2-Volume Set. St. Louis: Mosby. pp. 1315. ISBN 1-4160-2999-0. 
  28. ↑ DeBin JA, Strichartz GR (1991). "Chloride channel inhibition by the venom of the scorpion Leiurus quinquestriatus". Toxicon 29 (11): 1403–8. doi:10.1016/0041-0101(91)90128-E. PMID 1726031. 
  29. ↑ Deshane J, Garner CC, Sontheimer H (February 2003). "Chlorotoxin inhibits glioma cell invasion via matrix metalloproteinase-2". Journal of Biological Chemistry 278 (6): 4135–44. doi:10.1074/jbc.M205662200. PMID 12454020. 
  30. ↑ Frembgen, Jürgen Wasim (2004). "The Scorpion in Muslim Folklore". Asian Folklore Studies (Nanzan Institute for Religion and Culture) 63 (1): 95–123. http://www.jstor.org/stable/30030314. 

External links

Extant arthropod classes by subphylum
Kingdom Animalia · Subkingdom Eumetazoa · (unranked) Bilateria · (unranked) Protostomia · Superphylum Ecdysozoa
Chelicerata
Arachnida (Araneae · Scorpiones · Opiliones · Acari · Pseudoscorpionida · Amblypygi · Thelyphonida · Solifugae) · Xiphosura · Pycnogonida
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