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A scorpion is an invertebrate animal with eight legs belonging to the order Scorpiones in the class Arachnida.

Physical characteristics

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

Cephalothorax/prosoma: the scorpion's “head”, comprising the carapace, eyes, chelicerae (mouth parts), pedipalps (claw) and the four pairs of walking legs.

Mesooma: the abomen's ft half, is made up of six segments. The first segment contains the sexual organs as well as a pair of vestigial and modified appendages forming a structure called the genital operculum. The second segment bears a pair of featherlike sensory organs known as the pectines; the final four segments each contain a pair of book lungs. The mesosoma is armoured with chitinous plates, the tergites plates upper surface and the sternites plates the lower surface.

Metasoma: the scopion's tail, comprising six segments (the first tail segment looks like a last mesosoman segment), the last containing the scopion's anus and bearing the telson (the sting). The telson, in turn, consists of the vesicle, which holds a pair of venom (poison) glands and the hypodermic aculeus, the vemon injecting barbex.

Cuticle: this makes a tough armour around the body. In some places it is covered with hairs that act like balance organs. An outer layer that makes them fluoresce green under ultraviolet light is called the hyaline layer. Newly molted scorpions do not glow until after their cuticle has hardened. The fluoresent hyaline layer can be intact in hundreds of millions of year-old fossil rocks.

Main physical features

Pedipalps: the long front appendages that end in the so-called "claws" (the correct term is chelae or "pincers"). These originally were legs that were modified during evolution. The pedipalps are used primarily for prey capture but also play an important part in the scorpion mating dance. They are made of up of six segments. The chela (pincer) itself consists of the upper fixed finger (tibia) and the lower movable finger (tarsus). The pincers' size is highly dependent on the species; however, a general trend is that the more venomous the scorpion, the narrower the pincers, as scorpions with less potent venom use their larger pincers to subdue prey.

Pectines: these are a pair of feather-like sensory organs, consisting of a row of pegs, and are unique in scorpions. The pectines are located beneath the scorpion, attached to the sternum. They constantly touch the ground and play an important role in the scorpion's sensory equipment. The pectines are covered in thousands of chemosensors that allow the scorpion to detect minute chemical signals in their environment; they probably play an important role in social interaction, mating and hunting.

Eyes: fossil scorpions had compound eyes, modern scorpions in general have three sets of eyes. One pair located in the top centre of the carapace are called the median eyes. There are two more sets of lateral eyes on either side of the front of prosoma, the number varies between species. In total, there are usually from three and up to six pairs of eyes present. Some species of cave- and litter-dwelling scorpions, however, have no eyes, relying purely on their other senses. Scorpions' eyes are primitive organs, only able to detect regions of strongly contrasting light intensity, such as horizons. The eyes, however, are very sensitive; some have theorised that they even allow the scorpion to navigate by star light and help regulate the scorpion's circadian rhythm. It is doubtful as to whether they are used in prey capture.

Ears: scorpions can detect airborne sounds using tiny hairs on their claws.

Sound: scorpions make a characteristic sound similar to the rasping or chirping of cockroaches, albeit a bit higher pitched.

Two tails

On rare occasions, scorpions can be born with two metasoma (tails). Two-tailed scorpions are not a species, but rather a genetic abnormality.*

Scorpion venom

All scorpion species possess venom. In general, scorpion venom is described as neurotoxic in nature. One exception to this however is Hemiscorpius lepturus which possesses cytotoxic venom. It consists of a variety of small proteins as well as sodium and potassium cations, which serve to interfere with neurotransmission in the victim. 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.

Scorpion venoms are optimized for other arthropods and therefore most scorpions are relatively harmless to humans; stings produce only local effects (such as pain, numbness or swelling). However a few scorpion species, mostly in the family Buthidae, can be dangerous to humans. Among the most dangerous are Leiurus quinquestriatus, otherwise known as the death stalker, which has the most potent venom in the family, and members of the genuses Parabuthus, Tityus and especially Androctonus, which also have strong venom. These scorpions, and others in the family Buthidae, have been responsible for many human deaths. Scorpions are generally unable to deliver enough venom to kill healthy adults; deaths normally occur in the young, elderly or infirm. One symptom of a scorpion sting can include numbing at the injection site, sometimes lasting for several days. Unless provoked, scorpions are generally harmless and timid and use their sting only for killing prey. Generally, they will run from danger or remain very still.

It is unknown whether scorpions are venom conservers; however, the venom is often only used when the prey cannot be subdued with the claws alone. Many scorpion species, such as Pandinus and Hadogenes, rarely if ever use their venom, instead relying on their strong bulky pedipalps in prey capture.

Reproduction

Scorpions generally reproduce sexually and all species have male and female individuals. Reproduction is accomplished by the transfer of a spermatophore from the male to the female; scorpions have evolved 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 performs 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, probably as a means of pacifying the female.

When he 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 fertilising 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 break off the process.

Once the mating is complete, the male and female quickly 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

Unlike the majority of Arachnida, 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, depending on her for protection and to regulate their moisture levels. In some species, the young/mother association can continue for an extended period of time especially in species which display more advanced sociability (e.g Pandinus spp.). The size of the litter depends on the species and can range from three to 100+ scorplings Lourenco W. R., 2000, Reproduction in scorpions, with special reference to .

The young resemble their parents in a general way. Growth is accomplished by periodical shedding of the exoskeleton (ecdysis). A scorpion's developmental progress is measured in instars (how many moults it has undergone). Generally, scorpions require between five to 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; then, 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; however, as sclerotization occurs, the fluorescence gradually returns.

Scorpions have very variable lifespans and the actual lifespan of most species is not known; however, the range is approximately 4-25 years (25 years being the maximum reported life span of the species H. arizonensis).

Origins

Scorpion remains are often found in coal deposits that are believed to be of the Carboniferous Period, and no essential structural difference has been discovered between these fossils (such as Palaeophonus, Pulmonoscorpius and Paraisobuthus) and existing forms — suggesting that the group has existed without material structural modification for about 300 million years.

The eurypterids, marine creatures who lived during the Paleozoic era, share several physical traits with the scorpion and are closely related to it. They could grow to be anywhere between 10 cm (4 in) and 3 m (9.75 ft). However, they exhibit anatomical differences marking them off as a group distinct from their Carboniferous and recent descendants. Despite this, some refer to them 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, like the legs of shore-crabs, for maintaining a secure hold upon rocks or seaweed against the wash of waves.

Geographical distribution

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. Moreover, the occurrence of closely related forms in Australia and South America on the one hand, and in tropical Africa and the northern parts of South America on the other, suggests very forcibly that South America was at an early date connected with Australia by a transpacific bridge and with Africa by a more northern transatlantic tract of land.

In conformity with their wide dispersal, scorpions have become adapted to diverse conditions of existence, some thriving in rainforests, others on open plains, others in sandy deserts and a few even at high altitudes where the ground is covered with snow throughout the winter. In the tropics, they aestivate at times of drought; and in the Alps, they pass the cold months of the year in a state of hibernation.

In the United States, scorpions are most common in southern Arizona and in a swath extending through central Texas and central Oklahoma. The common striped scorpion, Centruroides vittatus, reaches from northwest Mexico to southern Colorado, Kansas, southern Missouri and Mississippi. Species of the genus Vaejovis are found from Florida north to Maryland, the Carolinas, and Tennessee and as far west as Oregon and California. Paruroctonus boreus is found through the Northwest US and into Canada. Scorpions can be found in 31 different states in the US, including Hawai'i (Isometrus maculatus).

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.

How scorpions eat

Scorpions generally use their chela (pincers) to catch the prey initially. Depending on their toxicity of their venom and size of their claws, they will then either crush it or inject it with neurotoxic venom. This will kill or paralyse the prey so the scorpion can eat it. Scorpions have a quite unique style of eating which uses chelicerae. These are small claw like structures which protrude from the mouth, only a handful of other animals have these including vinegaroons. Chelicerae are very sharp and are used to pull small amounts of food off the prey item for digestion. Scorpions can only digest food in a liquid form, any solid matter (fur, exoskeleton, etc) is disposed of by the scorpion.

Suicide misconception

The belief that scorpions commit suicide by stinging themselves to death when surrounded by fire is of considerable antiquity and is often prevalent where these animals exist. It is nevertheless untrue since the venom has no effect on the scorpion itself, nor on any member of the same species (unless the venom is injected directly into the scorpion's nerve ganglion). The misconception may derive from the fact that scorpions are cold-blooded: when exposed to intense heat their metabolic processes malfunction. This causes the scorpion to spasm wildly and this spasming may appear as if the scorpion is stinging itself. It is also untrue that alcohol will cause scorpions to sting themselves to death.

Radiation

It is said that scorpions can survive the radiation that results from the detonation of nuclear weapons. Indeed, scorpions have been observed surviving the radiation from nuclear weapons tests at French test sites in the Sahara Wee, Chua Kian. 1997. What is a scorpion http://web.singnet.com.sg/~chuaeecc/what/what.htm . Scorpions are also known to glow when exposed to certain types of ultraviolet radiation such as that which is produced by a blacklight.

Classification

This classification is based on that of Soleglad & Fet (2003) Soleglad, M. E. & V. Fet. 2003. High-level systematics and phylogeny of the extant scorpions (Scorpiones: Orthosterni). Euscorpius, 11, pp. 1-175. (download from http://www.science.marshall.edu/fet/euscorpius/pubs.htm) , which replaced the older, unpublished classification of Stockwell Scott A. Stockwell, 1989. Revision of the Phylogeny and Higher Classification of Scorpions (Chelicerata). Ph.D. Dissertation, University of California, Berkeley . Additional taxonomic changes are from Soleglad et al. (2005) .

  • Infraorder Orthosterni Pocock, 1911

Parvorder Pseudochactida Soleglad et Fet, 2003

Superfamily Pseudochactoidea Gromov, 1998

Parvorder Buthida Soleglad et Fet, 2003

Superfamily Buthoidea C. L. Koch, 1837

Parvorder Chaerilida Soleglad et Fet, 2003

Superfamily Chaeriloidea Pocock, 1893

Superfamily Chactoidea Pocock, 1893

Superfamily Iuroidea Thorell, 1876

Superfamily Scorpionoidea Latreille, 1802

Cultural symbolism

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

In Mesopotamia, Gilgamesh for example approaches mountains where scorpion folk guard the entrance. Additionally, the Akkadians called the constellation Scorpio, Girtab, meaning the Seizer, or Stinger and "Place Where One Bows Down".

In Egyptian mythology, the scorpion stands for Seth, the Trickster and brother of Nephthys, nemesis and opponent of Osiris, and Isis.

The Falaknuma palace of Hyderabad, India, is laid out in the shape of a scorpion with two stingers spreading out as wings to the north.

Other use

From a Biblical quotation, it is the term for a severe Roman scourge. Hard material was fixed onto multiple thongs to give them a flesh-tearing bite Kings 12:11: ...My father scourged you with whips; I will scourge you with scorpions. The choice of the name testifies how much the hellish pain caused by the small animal is to be feared.

Its tail supposedly was also part of the fabulous monster manticore.

Pesticides

Scorpions are difficult to control with pesticides alone. Therefore, the first control strategy is to modify the area surrounding a house.

  • Remove all trash, logs, boards, stones, bricks and other objects from around the home.
  • Keep grass closely mowed near the home. Prune bushes and overhanging tree branches away from the house. Tree branches can provide a path to the roof for scorpions.
  • Store garbage containers in a frame that allows them to rest above ground level.
  • Never bring firewood inside the house unless it is placed directly on the fire.
  • Install weather-stripping around loose fitting doors and windows.
  • Plug weep holes in brick veneer homes with steel wool, pieces of nylon scouring pad or small squares of screen wire.
  • Caulk around roof eaves, pipes and any other cracks into the home.
  • Keep window screens in good repair. Make sure they fit tightly in the window frame.

Wettable powder formulations provide better residual control for crawling pests when applying perimeter sprays. When using pyrethroids or other insecticides labeled for scorpion control, be sure to use the highest permissible label rate.

Apply pesticides around the foundation of the building and up to 1 foot above ground level on the exterior walls. Also apply pesticides around doors, window eaves and other potential points of entry.

Cyfluthrin, bifenthrin, deltamethrin, and bendiocarb are effective pesticides.*

See also

References

  • parthenogenesis, European Arachnology, pp. 71-85

External links

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This article is licensed under the GNU Free Documentation License. It uses material from the "Scorpion".

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