Scorpions

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

Main physical features

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 claw itself consists of the upper fixed finger and the lower movable finger . 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 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 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.

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, 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 with 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 - 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 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.

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. 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 . 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 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 and existing forms?suggesting that the group has existed without material structural modification for millions of 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 1 m (3 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 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.

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 .

Five colonies of scorpions 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 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 again for an entire 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 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.