Scorpion

? Scorpion
Arabian fat-tailed scorpion, Androctonus crassicauda
Scientific classification
Kingdom: Animalia Phylum: Arthropoda Subphylum: Chelicerata Class: Arachnida Order: Scorpiones C. L. Koch, 1837
Superfamilies
Pseudochactoidea Buthoidea Chaeriloidea Chactoidea Iuroidea Scorpionoidea See the classification sectionfor families.

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 2 main segments: the cephalothorax (also called the prosoma) and the abdomen/opisthosoma. The abdomen consists of the mesosoma and the metasoma.

Cephalothorax/prosoma: the “head” of the scorpion comprising the carapace, eyes, chelicerae (mouth parts), pedipalps ( claw) and the 4 pairs of walking legs.

Mesosoma: The first half of the abdomen and 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. And the final four segments each contains a pair of book lungs. The mesosoma is armoured with chitinous plates, on the upper surface by the tergites and on the lower surface by the sternites.

Metasoma: The tail of the scorpion comprising 6 segments (the first tail segment looks like a last mesosoman segment), the last containing the anus of the scorpion 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 barb used to inject the venom.

Cuticle: The cuticle makes a tough armour around the body. In some places it covered with hairs that acts like balance organs. An outer layer that makes them fluoresce in green under ultraviolet light is called the hyaline layer. Newly molted scorpions do not glow before after their cuticle has hardened. The hyaline layer is said to still be intact in hundreds of millions of years old fossil rocks, and it is still able to fluoresce.

Main scorpion physical features:

Pedipalps: The claws. Some believe these were originally modified legs that evolved into claws. The claws are used primarily for prey capture, but also play an important part in the scorpion mating dance. The pedipalps are made of up of 6 segments. The claw itself consists of the upper fixed finger ( tibia) and the lower movable finger ( tarsus). The size of the pedipalps is highly dependent on the species; however a general trend is that the more venomous the scorpion, the narrower the pedipalps, 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 compund eyes, present 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 are however very sensitive: some have theorised that they even allow the scorpion to navigate by star light, and they are important in regulating the scorpion's circadian rhythm. It is doubtful as to whether they are used in prey capture.

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

Scorpion venom

All species of scorpion possess venom. In general scorpion venom is described as neurotoxic in nature. 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 geared towards activity in 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 scorpions, mostly in the family Buthidae, can be dangerous to humans. Among the most dangerous are Leiurus quinquestriatus, which has the most potent venom in the family, and members of genus Parabuthus, Tityus and Androctonus whose venom is also strong. These scorpions and others in the family Buthidae have been responsible for many deaths, although scorpions are generally unable to deliver enough venom to kill healthy adults; deaths normally occur in the young, elderly or infirm. Unless molested, scorpions are generally harmless and timid, and only make use of the sting for the purpose of killing prey. Generally, they will run from danger, or remain very still. It is unknown whether scorpions are venom conservers, however often the venom is not used unless the prey cannot be subdued with the claws. Many species of scorpions 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 by the male and female locating and identifying each other using a mixture of pheromones and vibronic 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 meanings of pacifying the female.

When he has identified a suitable location he guides the female over the spermatophore allowing it to enter her genital opercula, this triggers release of the sperm; 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 females may eventually break off the process.

Once the mating is complete the male and female quickly separate: the male will generally retreat quickly 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 under gone 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 3 to 100+ scorplings .

The young in a general way 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). Generally scorpions require between 5-7 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, however as sclerotization occurs the fluorescence gradually returns.

Scorpions have very variable life spans and the actual life span 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 and existing forms—suggesting that the group has existed without material structural modification for millions of years. These scorpions were believed to be preceded by others, now occurring in marine Silurian deposits, which apparently lived in the sea and exhibit some anatomical differences marking them off as a group distinct from their Carboniferous and recent descendants and attesting affinity with the still earlier marine Arachnida referred to the group Gigantostraca. Their legs were thought to be short, thick, tapering, and ended in a single strong claw, and were well adapted, it seems, like the legs of shore-crabs, for maintaining a secure hold upon rocks or seaweed against the wash of waves. The method of breathing of these ancient types is not certainly known; but probably respiration was effected by means of book gills attached to the ventral plates of the body. At all events no trace of respiratory stigmata has been detected even in well-preserved material. These Silurian scorpions, of which the best-known genus is Palaeophonus, were of small size, only two to five centimeters in length.

Among known fossil scorpions are:-

• Brontoscorpio anglicus (Silurian-Devonian)
• Gigantoscorpio willsi ( Mississippian period, c.350 million years ago)
• Prearcturus gigas (Lower Devonian, c.390 million years ago).

These all are estimated to have reached over 3 feet in length. These were much too large to have molted without the support of water, and are thought to have been amphibious or wholly aquatic.

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, introduced).

A colony of scorpions has established itself in southern England having probably arrived with imported fruit from Africa.

How scorpions eat

Scorpions first catch their prey in their claws. If their prey is strong, they will paralyze it with their stinger. They then tear off a bit, digest it, and shoot acids out to dissolve the prey. They then suck up the prey. One full meal often takes two hours to eat completely.They may not have to eat for one whole year.

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 wherever 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.

Classification

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

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
  • • Subfamily Chactinae Pocock, 1893
      • Tribe Chactini Pocock, 1893
      • Tribe Nullibrotheini Soleglad et Fet, 2003
    • Subfamily Brotheinae Simon, 1879
      • Tribe Belisariini Lourenço, 1998
      • Tribe Brotheini Simon, 1879
        • Subtribe Brotheina Simon, 1879
        • Subtribe Neochactina Soleglad et Fet, 2003
    • Subfamily Uroctoninae
• 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
  • • Subfamily Bothriurinae Simon, 1880
    • Subfamily Lisposominae Lawrence, 1928
• Family Scorpionidae Latreille, 1802 ( burrowing scorpions or pale-legged scorpions)
  • • Subfamily Diplocentrinae Karsch, 1880
      • Tribe Diplocentrini Karsch, 1880
      • Tribe Nebini Kraepelin, 1905
    • Subfamily Scorpioninae Latreille, 1802
    • Subfamily Urodacinae Pocock, 1893
• 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

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. And 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 scourge on which the multiple thongs are fixed with hard materials, so as to give them a flesh-tearing bite.