Scorpion

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For other uses see Scorpion (disambiguation) and Scorpio (disambiguation).
Scorpion
Asian forest scorpion (Heterometrus spinifer) in Khao Yai National Park, Thailand
Asian forest scorpion (Heterometrus spinifer) in Khao Yai National Park, Thailand
Scientific classification
Kingdom: Animalia
Subphylum: Chelicerata
Class: Arachnida
Subclass: Dromopoda
Order: Scorpiones
C. L. Koch, 1837
Superfamilies

Pseudochactoidea
Buthoidea
Chaeriloidea
Chactoidea
Iuroidea
Scorpionoidea
See classification for families.

Scorpions are any arachnid of the order Scorpionida. They are members of the order Scorpiones within the class Arachnida. There are about 2,000 species of scorpions, found widely distributed south of about 49° N, except New Zealand and Antarctica. The northernmost part of the world where scorpions live in the wild is Sheerness on the Isle of Sheppey in the UK, where a small colony of Euscorpius flavicaudis has been resident since the 1860s.[1][2] The word scorpion derives from Greek σκορπιός - skorpios[3].

Contents

[edit] Anatomy

Centruroides sp.
E. mingrelicus

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

[edit] Cephalothorax

The cephalothorax, also called the prosoma, is the scorpion's “head”, comprising the carapace, eyes, chelicerae (mouth parts), pedipalps (claws) 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 and how far back or how far to the front has to do with the ground(soil) that the scorpion lives in, for example how hard or soft the ground is.[4]

[edit] 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.[5]

[edit] 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 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,[6] 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 cannibalized by the female, although sexual cannibalism is infrequent with scorpions.

[edit] 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 moult. Before the first moult, 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.[7]

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.

[edit] Venom

All known Scorpion species possess poison or venom. Scorpions use their venom to kill or paralyze their prey so that it can be eaten; in general it is fast-acting, allowing for effective prey capture. Scorpions are relatively timid creatures which are preyed on by a variety of larger predators, most of which can easily outmaneuver the scorpion and tear off its stinger. Some have even developed an evolved immunity to the venom so the scorpion can be devoured whole. Thus, when confronted by a larger creature, scorpions will generally run for the nearest cover.

[edit] Effects of scorpion stings on humans

The Australian Wood Scorpion's venom is not considered dangerous to humans

Of the ~1500 scorpion species, the vast majority are only capable of producing a local reaction similar in scope and effect to a bee sting. Only around 50 species are known to produce venom that causes serious systemic effects in humans. Of these 50 species, only a few (mostly in the family Buthidae) produce enough venom to pose a lethal risk to humans.

Still, severe reactions and death from stings are very common, accounting for thousands of deaths a year worldwide, 10 times as many as snake bites.[8] Most of the deaths attributed to scorpion stings occur in children, the elderly and the infirm in rural, agricultural areas of Africa, South America and Mexico, where the most venomous species are ubiquitous.

Scorpions rarely aggressively attack humans, but will often reflexively strike when they are handled, stepped on in bare feet, or accidentally crushed in clothing. Their ubiquity in certain rural areas and nocturnal, cold-blooded physiology often result in scorpions making their day burrows in human objects or dwellings. Footwear or clothing left outside overnight, thatched roofs, cracks in plaster or concrete, and wood and brush piles are all common shelter sites for scorpions.

Among the most dangerous are the deathstalker (L. quinquestriatus) and the yellow fat-tailed scorpion (A. australis), bearing the most potent venom and the highest human death toll in the Scorpion order (respectively). Both are native to the deserts and grasslands of North Africa and the Middle East, and account for nearly 75% of the worldwide deaths attributed to scorpion stings every year. Human deaths normally occur in the young, elderly, or sick; all but a few species are generally incapable of delivering enough venom to kill a human, although envenomations from one of the 50 most potent species generally causes unpleasant and temporarily debilitating systemic effects such as vomiting, cramps, blurred and wobbly vision, sensitivity to light, hypersalivation, difficulty swallowing, and agitation. Anaphylactic shock has also been caused by allergic reactions to several species of scorpion venom.

[edit] Scorpion stings in the United States

Of the 30 species of scorpions native to the United States, only the Arizona bark scorpion is capable of causing lethal reactions in humans. Bark scorpions widely vary in the amount of venom they inject; all envenomation generally causes severe pain and swelling at the sting site, but systemic symptoms are common in larger doses and can be severe. Bark scorpion stings cause death in less than 1% of untreated adults but fully 25% of untreated children 5 and under. Thousands are estimated to be stung in Arizona every year without seeking treatment; due to the unavailability of bark scorpion antivenom, the Arizona Poison Control currently advises against emergency room visits for bark scorpion stings unless the victim is a child, breathing difficulty is encountered, or the pain becomes intolerable. Both systemic and local symptoms typically subside within 24-48 hours.

[edit] Fossil record

Scorpions have been found in many fossil records, including marine Silurian deposits, coal deposits from the Carboniferous Period and in amber. They are thought to have existed in some form since about 430 million years ago. They are believed to have an oceanic origin, with gills and a claw-like appendage that enabled them to hold onto rocky shores or seaweed, although the assumption that the oldest scorpions were aquatic has been questioned. Currently, 111 fossil species of scorpion are known. 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 cm (4 in) to 2.5 m (8 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."[9] 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 shore-crab.

[edit] Geographical distribution

Hadrurus spadix - Iuridae, Hadrurinae

Scorpions are almost universally distributed south of 49° N, and their geographical distribution shows in many particulars a close and interesting correspondence with that of the mammals, including their entire absence from New Zealand. The facts of their distribution are in keeping with the hypothesis that the order originated in the northern hemisphere and migrated southwards into the southern continent at various epochs, their absence from the countries to the north of the above-mentioned latitudes being due, no doubt, to the comparatively recent glaciation of those areas. When they reached Africa, Madagascar was part of that continent; but their arrival in Australia was subsequent to the separation of New Zealand from the Austro-Malayan area to the north of it.

In the United States, scorpions are most common in southern Arizona and in a swath of land extending through central Texas and central Oklahoma. The common striped scorpion, Centruroides vittatus, reaches from northern and northeastern Mexico to southern Colorado, Kansas, southern Missouri, and Louisiana. A small population is native to Monroe County, Illinois. Species of the genus Vaejovis are found from Georgia north to Kentucky, the Carolinas, and Tennessee, and as far west as Washington and California. Paruroctonus boreus is found through the Northwest U.S. and into Canada (Southern Saskatchewan, Southern Alberta and the Okanagan Valley of British Columbia). Scorpions can be found in 31 different states in the U.S., including Hawaii (Isometrus maculatus). They are absent from areas that were affected by Pleistocene glaciation in the eastern U.S. California and Arizona boast the greatest scorpion species diversity, although areas in the Trans-Pecos region of Texas have 9 species within 100 meters.

Five colonies of scorpions (Euscorpius flavicaudis) have established themselves in southern England 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.

[edit] Ultraviolet light

A scorpion under a blacklight. 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. The principal fluorescent component is now known to be beta-Carboline.[10] A hand-held UV lamp has long been a standard tool for nocturnal field surveys of these animals. Please note however, a glow will only be produced in adult specimens. The substances in the skin required to produce the glow are not found in adolescents. [11]

[edit] Classification

This classification is based on that of Soleglad & Fet (2003),[12] which replaced the older, unpublished classification of Stockwell.[13] Additional taxonomic changes are from Soleglad et al. (2005).[14]

[edit] Cultural symbolism

 This section does not cite any references or sources. Please help improve this article by adding citations to reliable sources (ideally, using inline citations). Unsourced material may be challenged and removed. (June 2008)

The scorpion has had various meanings and representations in different cultures in history:

  • In the Epic of Gilgamesh, Gilgamesh approaches mountains where scorpion-folk guard the entrance. Additionally, the Akkadians called the constellation Scorpius, Girtab, meaning "the Seizer", or "Stinger" and "Place Where One Bows Down".
  • In ancient Egypt, the scorpion was associated with the god Set- the god of the desert, storms, and chaos.
  • The Falaknuma Palace of Hyderabad, India, is laid out in the shape of a scorpion with the two pincers spreading out to the north as wings to the building.
  • In Greek mythology, the scorpion is conjured by the gods to hound and punish Orion. It is also said that when Perseus slew Medusa, the blood that leaked out of her severed neck turned into scorpions and snakes as it hit the ground.
  • The Persian legendary monster manticore is often depicted with a scorpion tail.
  • The scorpion is one of the symbols of the Astrological sign of Scorpio.
  • The scorpion is the symbol of the Mexican state of Durango.
  • The scorpion is the symbol of the Italian auto tuning company Abarth.

[edit] See also

Sister project Wikispecies has information related to: Scorpiones
Sister project Wikimedia Commons has media related to: Scorpiones

Several species bear the name "scorpion" but do not belong to the order Scorpiones:

[edit] References

  1. ^ Benton, T. G. (1991). "The Life History of Euscorpius Flavicaudis (Scorpiones, Chactidae)". The Journal of Arachnology 19: 105–110. http://www.americanarachnology.org/JoA_free/JoA_v19_n2%20/JoA_v19_p105.pdf. Retrieved on 2008-06-13. 
  2. ^ 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 on 2008-06-13. 
  3. ^ Skorpios, Henry George Liddell, Robert Scott, A Greek-English Lexicon, at Perseus
  4. ^ http://insects.tamu.edu/extension/bulletins/l-1678.html
  5. ^ Prchal, Steve. "Pepe the Two Tailed Scorpion". Sonoran Arthropod Studies Institute. http://www.sasionline.org/pepe.htm. Retrieved on 2008-06-13. 
  6. ^ 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. 
  7. ^ Lourenco, W. R. (2000). "Reproduction in scorpions, with special reference to parthenogenesis". European Arachnology: 71–85. 
  8. ^ http://emedicine.medscape.com/article/168230-overview
  9. ^ Waggoner, Ben. "Eurypterida". Regents of the University of California. http://www.ucmp.berkeley.edu/arthropoda/chelicerata/eurypterida.html. Retrieved on 2008-06-13. 
  10. ^ 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 on 2008-06-17. 
  11. ^ Hadley, Neil F.; Stanley C. Williams (July 1968). "Surface Activities of Some North American Scorpions in Relation to Feeding". Ecology (Ecological Society of America) 49 (4): 726–734. doi:10.2307/1935535. http://www.jstor.org/pss/1935535. Retrieved on 2008-06-17. 
  12. ^ 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 on 2008-06-13. 
  13. ^ Scott A. Stockwell, 1989. Revision of the Phylogeny and Higher Classification of Scorpions (Chelicerata). Ph.D. Dissertation, University of California, Berkeley
  14. ^ 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 on 2008-06-13. 

[edit] External links

Retrieved from "http://en.wikipedia.org/wiki/Scorpion"
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