Scientific classification
Kingdom: Animalia
Phylum: Arthropoda
Subphylum: Chelicerata
Class: Arachnida
Subclass: Dromopoda
Order: Scorpiones
C. L. Koch, 1837

Scorpions are predatory arachnids of the order Scorpiones. They have eight legs[1] and are easily recognised by the pair of grasping pedipalps and the narrow, segmented tail, often carried in a characteristic forward curve over the back, ending with a venomous stinger. Scorpions range in size from 9 mm (Typhlochactas mitchelli) to 23 cm (Heterometrus swammerdami).[2]

The evolutionary history of scorpions goes back to the Silurian era 430 million years ago. They have adapted to a wide range of environmental conditions and can now be found on all continents exceptAntarctica. Scorpions number about 1750 described species,[3] with 13 extant families recognised to date. Only about 25 of these species are known to have venom capable of killing a human being.[4]:1The taxonomy has undergone changes and is likely to change further, as genetic studies are bringing forth new information.

Scorpion stings are painful but are usually harmless. For stings from species found in the United States, no treatment is normally needed for healthy adults although medical care should be sought for children and for the elderly. Stings from species found elsewhere may require medical attention.[5]

Etymology

The word scorpion is thought to have originated in Middle English between 1175 and 1225 AD from Old French scorpion,[6] or from Italian scorpione, both derived from the Latin word scorpius,[7] which is theromanization of the Greek word σκορπίοςskorpíos.[8]

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 now have been accidentally introduced in some of these places by human trade and commerce.[4]:249 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 natural occurrence of scorpions being the northern scorpion Paruroctonus boreus at Medicine Hat, Alberta, Canada 50° N.[4]:251

Today, scorpions are found in virtually every terrestrial habitat, including high-elevation mountains, 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.[4]:251–252[9] 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 specialized niches such as Euscorpius carpathicus, which occupies the littoral zone of the shore.[10]

Five colonies of scorpions (Euscorpius flavicaudis) have established themselves in Sheerness on the Isle of Sheppey in the United Kingdom.[11] 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. At just over 51° N, this marks the northernmost limit where scorpions live in the wild.[12][13]

Classification

Main article: Taxonomy of scorpions

There are thirteen families and about 1,750 described species and subspecies of scorpions. In addition, there are 111 described taxa of extinct scorpions.[14]

This classification is based on that of Soleglad & Fet (2003),[15] which replaced the older, unpublished classification of Stockwell.[16] Additional taxonomic changes are from papers by Soleglad et al. (2005).[17][18]

Systematics

The following classification covers extant taxa to the rank of family.

Order Scorpiones

Fossil record

Proscorpius osborni, fossil scorpion initially thought to be a eurypterid

Scorpions have been found in many fossil records, including marine Silurian and estuarine Devonian deposits, coal deposits from the Carboniferous Period and in amber. The oldest known scorpions lived around 430 million years ago in the Silurian period. Though once believed to have lived on the bottom of shallow tropical seas,[19] early scorpions are now believed to have been terrestrial and to have washed into marine settings together with plant matter. These first scorpions were believed to have had gills instead of the present forms' book lungs though this has subsequently been refuted.[20][21][22] The oldest Gondwanan scorpiones (Gondwanascorpio) comprise the earliest known terrestrial animals from Gondwana.[23] Currently, 111 fossil species of scorpion are known.[14] Unusually for arachnids, there are more species of Palaeozoic scorpion than Mesozoic or Cenozoic ones.

The eurypterids, marine creatures that lived during the Palaeozoic 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 centimetres (3.9 in) to 2.5 metres (8.2 ft) in length.[24] 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 "sea scorpions".[25] 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. Cladistic analyses have supported the idea that the eurypterids are a distinct group from the scorpions.[26]

Morphology

Scorpion anatomy:
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 Aculeus ;
11 = Telson (follows anus in previous joint).

Front of scorpion

Stinger of an Arizona bark scorpion

Ventral view of an unidentified scorpion species where the pectinescan easily be observed with a comb like structure in an inverted V shape.

The body of a scorpion is divided into two parts (tagmata): the head (cephalothorax) and the abdomen (opisthosoma). This one is subdivided into a broad anterior (mesosoma), or preabdomen, and a narrow taillike posterior (metasoma), or postabdomen.[4]:10

Cephalothorax

The cephalothorax, also called the prosoma, comprises the carapace, eyes, chelicerae (mouth parts), pedipalps (the pedipalps of scorpions have chelae, commonly called claws or pincers) and four pairs of walking legs. The scorpion's exoskeleton is thick and durable, providing good protection from predators. Scorpions have two eyes on the top of the cephalothorax, and usually two to five pairs of eyes along the front corners of the cephalothorax. The position of the eyes on the cephalothorax depends in part on the hardness or softness of the soil upon which they spend their lives.[27]

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 (including the fixed claw and the manus) and tarsus (moveable claw).[28] A scorpion has darkened or granular raised linear ridges, called "keels" or carinae on the pedipalp segments and on other parts of the body, which are useful taxonomically.[4]:12

Mesosoma

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 covering the gonopore. Segment 2 consists of the basal plate with the pectines, which are a pair of limbs transformed into sensory organs.[29] Each of the mesosomal segments 3 to 7 have a pair of spiracles, the openings for the scorpion's respiratory organs, known as book lungs. The spiracle openings may be slits, circular, elliptical, or oval.[4]:13–15

Metasoma

The metasoma, the scorpion's tail, comprises five caudal segments (the first tail segment looks like a last mesosoman segment) and the sixth 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.[30]

Fluorescence

This black scorpion appears light-blue under a black light.

Scorpions are also known to glow a vibrant blue-green 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.[31] A hand-held UV lamp has long been a standard tool for nocturnal field surveys of these animals. Fluorescence occurs as a result of sclerotisation and increases in intensity with each successive instar.[31] This fluorescence may have an active role in scorpion light detection.[32]

Relationship with humans

Sting and venom

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. However, as a general rule they will kill their prey with brute force if they can, as opposed to using venom. 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 1,000+ known species of scorpion, only 25 have venom that is deadly to humans; most of those belong to the family Buthidae (including Leiurus quinquestriatus,Hottentotta, Centruroides and Androctonus).[10][39]

Treatment

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.[40] Scorpion envenomation with high morbidity and mortality is usually due to either excessive autonomic activity and cardiovascular toxic effects or neuromuscular toxic effects. Antivenin is the specific treatment for scorpion envenomation combined with supportive measures including vasodilators in patients with cardiovascular toxic effects and benzodiazepines when there is neuromuscular involvement. Although rare, severe hypersensitivity reactions including anaphylaxis to scorpion antivenin (SAV) are possible.[41]

Medical use

The deathstalker has powerful venom.

Short-chain scorpion toxins constitute the largest group of potassium (K+) channel blocking peptides; an important physiological role of the KCNA3 channel, also known as KV1.3, is to help maintain large electrical gradients for the sustained transport of ions such as Ca2+ that controls T lymphocyte (T cell) proliferation. Thus KV1.3 blockers could be potential immunosuppressants for the treatment of autoimmune disorders (such as rheumatoid arthritis, inflammatory bowel disease and multiple sclerosis).[42]

The venom of Uroplectes lineatus is clinically important in dermatology.[43]

Toxins being investigated include the following:

Production[edit]

Scorpions for use in the pharmaceutical industry are collected from the wild in Pakistan. Farmers in the Thatta District are paid about US$100 for each 40 gram scorpion and 60 gram specimens are reported to fetch at least US$50,000.[49] The trade is reported to be illegal but thriving.[50]

Consumption

Eating scorpions in Beijing, China

Fried scorpion is a traditional dish from Shandong, China.[51]

As a part of Chinese medicine, scorpion wine and snake wine are used as analgesic and antidote.

In culture

  • In North Africa and South Asia, the scorpion is a significant animal culturally, appearing as a motif in art, especially in Islamic art in the Middle East.[52] It is perceived both as an embodiment of evil as well as a protective force that counters evil, such as a dervish's powers to combat evil.[52] In another context, the scorpion portrays human sexuality.[52] Scorpions are used in folk medicine in South Asia especially in antidotes for scorpion stings.[52]