Scorpions are predatory arthropod animals of the order Scorpions within the class Arachnida. They have eight legs and are easily recognized by the pair of grasping claws and the narrow, segmented tail, carried in a characteristic forward curve over the back, ending with a venomous stinger.
Scorpions are found widely distributed over all continents, except Antarctica, in a variety of terrestrial habitats except the high latitude tundra. Scorpions number about 1752 described species, with thirteen extant families recognized to date. The taxonomy has undergone changes and is likely to change further, as a number of genetic studies are bringing forth new information.
Though the scorpion has a fearsome reputation as venomous, only 25 species have venom capable of killing a human being.
Scorpion Geographical Distribution
Scorpions are found on all major land masses except Antarctica. Scorpions did not occur naturally in Great Britain, New Zealand and some of the islands in Oceania, but have now been accidentally introduced in some of these places by human trade and commerce. The greatest diversity of scorpions in the Northern Hemisphere is to be found in the subtropical areas lying between latitudes 23° N and 38° N. Above these latitudes, the diversity decreases, with the northernmost occurrence of scorpions being the northern scorpion Paruroctonus boreus at 50° N.
Scorpions are found in virtually every habitat, including high elevation mountain-tops, caves and intertidal zones, with the exception of boreal ecosystems such as the tundra, high-altitude taiga and the permanently snow-clad tops of some mountains. As regards microhabitats, scorpions may be ground-dwelling, tree-living, lithophilic (rock-loving) or psammophilic (sand-loving); some species such as Vaejovis janssi are versatile and found in every type of habitat in Baja California while others occupy specialised niches such as Euscorpius carpathicus which occupies the littoral zone of the shore.
Five colonies of scorpions (Euscorpius flavicaudis) have established themselves in Sheerness on the Isle of Sheppey in the United Kingdom. This small population has been resident since the 1860s, having probably arrived with imported fruit from Africa. This scorpion species is small and completely harmless to humans. This marks the northernmost limit in the world where scorpions live in the wild.
Main article: Taxonomy of scorpions
There are thirteen families and about 1,400 described species and subspecies of scorpions. In addition, there are 111 described taxa of extinct scorpions.
This classification is based on that of Soleglad & Fet (2003), which replaced the older, unpublished classification of Stockwell. Additional taxonomic changes are from papers by Soleglad et al. (2005).
Scorpions have been found in many fossil records, including marine Silurian deposits, coal deposits from the Carboniferous Period and in amber. The oldest known scorpions lived around 430 million years ago in the Silurian period, on the bottom of shallow tropical seas. These first scorpions had gills instead of the present formsâ€™ book lungs. 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 to 25 centimetres (3.9 to 9.8 in) 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 â€œsea scorpionsâ€. 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 a shore crab.
1 = Cephalothorax or Prosoma;
2 = Abdomen or Mesosoma;
3 = Tail or Metasoma;
4 = Claws or Pedipalps
5 = Legs;
6 = Mouth parts or Chelicerae;
7 = pincers or Chelae;
8 = Moveable claw or Tarsus;
9 = Fixed claw or Manus;
10 = Sting or Telson;
11 = Anus.
The body of a scorpion is divided into three parts (tagmata): the head (cephalothorax), the abdomen (mesosoma) and the tail (metasoma).
The cephalothorax, also called the prosoma, is the scorpions head, comprising the carapace, eyes, chelicerae (mouth parts), pedipalps (commonly called claws, pincers or chelae) and four pairs of walking legs. The scorpions 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 depends in part on the hardness or softness of the soil upon which they spend their lives.
The pedipalp is a segmented, chelate (clawed) appendage used for prey immobilization, defense, and sensory purposes. The segments of the pedipalp (from closest to the body outwards) are coxa, trochanter, femur (humerus), patella, tibia (tarsus, hand or movable claw) and manus (fixed claw). A scorpion has darkened or granular raised linear ridges, called â€œkeelsâ€ or carinae on the pedipalp segments and on other parts of the body which are useful taxonomically.
The abdomen, also called the opisthosoma, consists of seven segments (somites), each covered dorsally by a sclerotosed plate (tergum) and also ventrally for segments 3 to 7. The first abdominal segment bears a pair of genital opercula which cover the gonopore. Segment 2 consists of the basal plate with the pectines. Each of the mesosomal segments 3 to 7 have a pair of spiracles which are the openings for the scorpions respiratory organs, known as book lungs. The spiracle openings may be slits, circular, elliptical, or oval.
The metasoma, the scorpions tail, comprises five caudal segments (the first tail segment looks like a last mesosoman segment), the last containing the scorpions 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.
Scorpion Fluorescence in Ultraviolet Light:
A scorpion under a black light appears fluorescent. 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 black-light, due to the presence of fluorescent chemicals in the cuticle. One fluorescent component is now known to be beta-carboline. A hand-held UV lamp has long been a standard tool for nocturnal field surveys of these animals. Fluorescence occurs as a result of sclerotization and increases in intensity with each successive instar.
Scorpion Life and Habits Scorpions have quite variable lifespans and the actual lifespan of most species is not known. The age range appears to be approximately 25 years (25 years being the maximum reported life span in the species Hadrurus arizonensis).
They are nocturnal and fossorial, finding shelter during the day in the relative cool of underground holes or undersides of rocks and coming out at night to hunt and feed. Scorpions exhibit photophobic behavior, primarily to evade detection by their predators such as birds, centipedes, lizards, mice, possums, and rats.
Scorpions are opportunistic predators of small arthropods and insects, although the larger kinds have been known to kill small lizards and mice. The large pincers are studded with highly sensitive tactile hairs, and the moment an insect touches these, they use their chelae (pincers) to catch the prey. Depending on the toxicity of the scorpion 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 relatively unique style of eating using chelicerae, small claw-like structures that protrude from the mouth that are unique to the Chelicerata among arthropods. The chelicerae, which are very sharp, are used to pull small amounts of food off the prey item for digestion into a pre-oral cavity below the chelicerae and carapace. Scorpions can only ingest food in a liquid form; they have external digestion. The digestive juices from the gut are egested onto the food and the digested food sucked in liquid form. Any solid indigestible matter (fur, exoskeleton, etc.) is trapped by setae in the pre-oral cavity, which is ejected by the scorpion. Scorpions can consume huge amounts of food at one sitting. They have a very efficient food storage organ and a very low metabolic rate combined with a relatively inactive lifestyle. This enables scorpions to survive long periods when deprived of food; some are able to survive 6 to 12 months of starvation. Scorpions excrete very little; their waste consists mostly of insoluble nitrogenous waste such as xanthine, guanine and uric acid.
Scorpion 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 unfertilised eggs develop into living embryos. Parthenogenic reproduction starts following the scorpionâ€™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 the other that they are of opposite sex and of the correct species, mating can commence.
Once the mating is complete, the male and female will separate. The male will generally retreat quickly, most likely to avoid being cannibalised by the female, although sexual cannibalism is infrequent with scorpions.
Scorpion 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 motherâ€™s back until the young have undergone at least one molt. Before the first molt, 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.
The young generally resemble their parents. Growth is accomplished by periodic shedding of the exoskeleton (ecdysis). A scorpions developmental progress is measured in instars (how many moults it has undergone). Scorpions typically require between five and seven moults to reach maturity. Moulting commences with a split in the old exoskeleton 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 scorpions 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.
All known scorpion species possess venom and use it primarily to kill or paralyze their prey so that it can be eaten; in general it is fast-acting, allowing for effective prey capture. It is also used as a defense against predators. The venom is a mixture of compounds (neurotoxins, enzyme inhibitors, etc.) each not only causing a different effect, but possibly also targeting a specific animal. Each compound is made and stored in a pair of glandular sacs and is released in a quantity regulated by the scorpion itself. Of the 1000+ known species of scorpion, only 25 have venom that is dangerous to humans; all belong to the family Buthidae.
Scorpion Sting First Aid
First aid for scorpion stings is generally symptomatic. It includes strong analgesia, either systemic (opiates or paracetamol) or locally applied (such as a cold compress). Hypertensive crises are treated with anxiolytics and vasodilators.
Toxins being investigated include:
* Chlorotoxin is a 36-amino acid peptide found in the venom of the deathstalker scorpion (Leiurus quinquestriatus) which blocks small-conductance chloride channels. The fact that chlorotoxin binds preferentially to glioma cells has allowed the development of new methods, that still are under investigation, for the treatment and diagnosis of several types of cancer. * Maurotoxin from the venom of the Tunisian Scorpio maurus palmatus