Scorpion
From Wikipedia, the free encyclopedia
- For other uses, see Scorpion (disambiguation).
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 Arabian fat-tailed scorpion, Androctonus crassicauda
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Pseudochactoidea |
A scorpion is an invertebrate animal with eight legs, belonging to the order Scorpiones in the class Arachnida.
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[edit] 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.
Mesosoma: the abdomen's front 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 armored with chitinous plates, the tergites plates upper surface and the sternites plates the lower surface.
Metasoma: the scorpion's tail, comprising 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 (poison) glands and the hypodermic aculeus, the vemon injecting barbex.
Cuticle: this makes a tough armor 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 fossil rocks that are hundreds of millions of years old.
[edit] Main physical features
Pedipalps: the long front appendages that end in the so-called "claws" (the correct term is chelae or "pincers"). Some believe these were originally 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.
[edit] 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.[1].
[edit] 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. The neurotoxins consist 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 action upon other arthropods and therefore most scorpions are relatively harmless to humans; stings produce only local effects (such as pain, numbness or swelling). A few scorpion species, however, mostly in the family Buthidae, can be dangerous to humans. Among the most dangerous are Leiurus quinquestriatus, otherwise dubiously known as the deathstalker, which has the most potent venom in the family, and members of the genera Parabuthus, Tityus, Centruroides, and especially Androctonus, which also have strong venom. The scorpion which is responsible for the most human deaths is the Androctonus australis, or fat-tailed scorpion of North Africa. The toxicity of A. australis's venom is roughly half that of Leiurus quinquestriatus, but since A. australis injects quite a bit more venom into its prey, it is the most deadly to humans. Human deaths normally occur in the young, elderly, or infirm; scorpions are generally unable to deliver enough venom to kill healthy adults. Some people, however may be allergic to the venom of some species, in which case the scorpion's sting can more likely kill. A primary symptom of a scorpion sting is numbing at the injection site, sometimes lasting for several days. Scorpions are generally harmless unless provoked, however. Scorpions are generally harmless and timid, and only voluntarily use their sting only for killing prey or defending themselves. Generally, they will run from danger or remain very still.
Scorpions are able to regulate how much venom is injected with each sting using striated muscles in the stinger, the usual amount being between 0.1 and 0.6 mg. There is also evidence to suggest that scorpions restrict the use of their venom using it only to subdue large prey, or prey that struggles. This is likely because it is expensive in terms of energy for a scorpion to produce venom, and because it may take several days for a scorpion to replenish its venom supply once it has been exhausted.[2][3]
[edit] Reproduction
Scorpions 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 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 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 (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 body[4]), 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.
[edit] Birth and development
Unlike the majority of Arachnida 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, depending 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 can range from three to 100+ scorplings [5].
The young generally resemble their parents. 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). 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.
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 H. arizonensis).
[edit] 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 which lived during the Paleozoic era, share several physical traits with scorpions and are closely related to it. Various species of Eurypterida could grow to be anywhere from 10 cm (4 in) to 3 m (9.75 ft) in length. 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." [1]. 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-crabs.
[edit] 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 of land 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 U.S. and into Canada. Scorpions can be found in 31 different states in the U.S., including Hawaii (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.
Sahara Scorpion:
The arthropod most commonly associated with deserts, scorpions in the Sahara come in 30 different varieties, most from the family Buthidae. Four of the Sahara's scorpion species are lethal to humans. In humans, their venom can cause temporary paralysis, convulsions, cardiac arrest, or respiratory failure. The vemon of some scorpion species is as toxic as that of a cobra. Saharan scorpions primarily limit their activity to the night, burrowing into the cooler sands beneath the desert's surface during the day. It absorbs water from the flesh of its prey.
[edit] How scorpions eat
Scorpions generally use their chela (pincers) to catch the prey initially. 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 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 spiders and 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.
[edit] 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—quite an unlikely event outside of the laboratory). The misconception may derive from the fact that scorpions are poikilotherms (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.
[edit] Radiation
It is said that scorpions can survive high levels of radiation, such as that which 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 [6]. Scorpions are also known to glow when exposed to certain types of ultraviolet light such as that which is produced by a blacklight. [2]
[edit] Classification
This classification is based on that of Soleglad & Fet (2003) [7], which replaced the older, unpublished classification of Stockwell [8]. Additional taxonomic changes are from Soleglad et al. (2005) [citation needed].
- 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
- Subfamily Euscorpiinae Laurie, 1896
- Subfamily Megacorminae Kraepelin, 1905
- Tribe Chactopsini Soleglad et Sissom, 2001
- Tribe Megacormini Kraepelin, 1905
- Subfamily Scorpiopinae Kraepelin, 1905
- Tribe Scorpiopini Kraepelin, 1905
- Tribe Troglocormini Soleglad et Sissom, 2001
- Family Superstitioniidae Stahnke, 1940
- Subfamily Superstitioniinae Stahnke, 1940
- Subfamily Typlochactinae Mitchell, 1971
- Family Vaejovidae Thorell, 1876
Superfamily Iuroidea Thorell, 1876
- Family Iuridae Thorell, 1876
- Family Caraboctonidae Kraepelin, 1905 (hairy scorpions)
- Subfamily Caraboctoninae Kraepelin, 1905
- Subfamily Hadrurinae Stahnke, 1974
Superfamily Scorpionoidea Latreille, 1802
- Family Bothriuridae Simon, 1880 /small
- Subfamily Bothriurinae Simon, 1880
- Subfamily Lisposominae Lawrence, 1928
- Family Scorpionidae Latreille, 1802 (burrowing scorpions or pale-legged scorpions)
- Family Hemiscorpiidae Pocock, 1893 (= Ischnuridae, =Liochelidae) (rock scorpions, creeping scorpions, or tree scorpions)
- Subfamily Hemiscorpiinae Pocock, 1893
- Subfamily Heteroscorpioninae Kraepelin, 1905
- Subfamily Hormurinae Laurie, 1896
[edit] 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 Set, 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.
[edit] 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 [1 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.
[edit] Pest control
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.[3]
[edit] See also
[edit] References
- ^ http://www.sasionline.org/pepe.htm
- ^ Scorpion Sting
- ^ Sting Use In Two Species of Parabuthus Scorpions (Buthidae)
- ^ http://www.key-net.net/users/swb/pet_arthropod/frs.htm
- ^ Lourenco W. R., 2000, Reproduction in scorpions, with special reference to parthenogenesis, European Arachnology, pp. 71-85
- ^ Wee, Chua Kian. 1997. What is a scorpion http://web.singnet.com.sg/~chuaeecc/what/what.htm
- ^ 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)
- ^ Scott A. Stockwell, 1989. Revision of the Phylogeny and Higher Classification of Scorpions (Chelicerata). Ph.D. Dissertation, University of California, Berkeley
[edit] External links
- [4]- Sahara Desert wildlife information
- The Scorpion Files- Most comprehensive online resource of scorpion information
- Arachnodata; Information & Consulting Agency for scorpions and arachnids
- EUSCORPIUS, the online research journal of scorpiology — has many important scorpion links
- List of the LD50 value for the venom of various species of scorpion
- Arachnoboards- Online arachnid discussion group
- U.S. state-by-state Scorpiones checklist
- Kari's Scorpion Pages
- Dr. Scott A. Stockwell's Scorpion Emporium (currently down)
- Information on scorpions and other arachnids
- Pepe the two-tailed scorpion
- Scorpion detection using UV LEDs (also movies of scorpions)
- Desert USA: Scorpions
- Photo gallery of several scorpions in captive breeding.
- Scorpion Venom Tested as Brain Cancer Treatment
![[2]](http://www.public.asu.edu/~bbackes/images/scorpion2.jpg){kind=link}