Scorpions

**Scorpions** are predatory arthropod animals of the order **Scorpiones** within the class Arachnida. They have eight legs 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 20 cm (*Hadogenes troglodytes*).

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 except Antarctica. Scorpions number about 1750 described species, with 13 extant families recognised to date. Only about 25 of these species are known to have venom capable of killing a human being. The taxonomy has undergone changes and is likely to change further, as genetic studies are bringing forth new information.

## ***Anatomy***

The body of a scorpion is divided into three parts (tagmata): the head (cephalothorax), the abdomen(mesosoma) and the tail (metasoma).

### 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.

The pedipalp is a segmented, chelate (clawed) appendage used for prey immobilisation, defence 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). 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.

### Mesosoma

The abdomen, also called the *opisthosoma*, consists of seven segments (somites), each covereddorsally 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. 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.

### 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.

### Fluorescence

Scorpions are also known to glow a vibrant blue-green when exposed to certain wavelengths of ultraviolet light such as that produced by ablack 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 ofsclerotisation and increases in intensity with each successive instar. This fluorescence may have an active role in scorpion light detection.

## ***Biology***

Scorpions prefer areas where the temperatures range from 20 to 37 °C (68 to 99 °F), but may survive temperatures ranging from well below freezing to desert heat.[31][32] Scorpions of the genus *Scorpiops* living in high Asian mountains, bothriurid scorpions from Patagonia and small *Euscorpius* scorpions from Central Europe can all survive winter temperatures of about −25 °C (−13 °F). In Repetek(Turkmenistan), there live seven species of scorpions (of which *Pectinibuthus birulai* is endemic) in temperatures varying from −31 to 50 °C (−24–122 °F).

They are nocturnal and fossorial, finding shelter during the day in the relative cool of underground holes or undersides of rocks, and emerging at night to hunt and feed. Scorpions exhibit photophobic behavior, primarily to evade detection by predators such as birds, centipedes, lizards, mice, possums and rats.

Scorpions are opportunistic predators of small arthropods, 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 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 an unusual style of eating usingchelicerae, 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 ingest food only 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 compounds such as xanthine, guanine and uric acid.

### 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 scorpion'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.

The courtship starts with the male grasping the female's pedipalps with his own; the pair then perform a "dance" called the "*promenade à deux*". In this "dance," the male leads 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 – pincers – 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 pedipalp or on the edge of her cephalothorax, probably as a means of pacifying the female.

When the male 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 continues too long, the female may lose interest, ending the process.

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.

#### Birth & Development

Unlike the majority of species in the class Arachnida, which are oviparous, scorpions seem to be universally ovoviviparous. The young are born one by one after hatching and expelling the embryonic membrane, if any, 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, since they depend on her for protection and to regulate their moisture levels. Especially in species that 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 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 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 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 sclerotisation. The new exoskeleton does not fluoresce; as sclerotisation occurs, the fluorescence gradually returns.

## ***Genera***

### Family **Buthidae**

#### Genus ***Centruroides*** - Bark Scorpions

* ***gracilis*** - Florida Bark Scorpion
* ***hentzi*** - Hentz Striped Scorpion
* ***sculpturatus*** - Arizona Bark Scorpion

* ***vittatus*** - Striped Bark Scorpion

Family **Diplocentridae** ===
Genus ***Diplocentrus*** - Toothed Scorpions

* ***diablo*** - Diplocentrus diablo

* ***lindo*** - Diplocentrus lindo
* ***peloncillensis*** - Diplocentrus peloncillensis
* ***spitzeri*** - Diplocentrus spitzeri
* ***whitei*** - Diplocentrus whitei

### Family **Iuridae**

Genus ***Anuroctonus***

* ***pococki*** - California swollenstinger scorpion

* ***pococki*** - Anuroctonus pococki pococki

* ***phaiodactylus*** - Swollenstinger Scorpion

Genus ***Hadrurus*** - Giant Hairy Scorpions

* ***anzaborrego*** - Anza-Borrego hairy scorpion

* ***arizonensis*** - Arizona Hairy Scorpion

* ***obscurus*** - Hadrurus obscurus

* ***spadix*** - Black Hairy Scorpion

### Family **Superstitioniidae**

Genus ***Superstitionia***

* ***donensis*** - Superstition Mountains Scorpion

### Family **Vaejovidae**

Genus ***Paruroctonus***

* ***becki*** - Paruroctonus becki
* ***boreus*** - Northern Scorpion
* ***gracilior*** - Chihuahuan Slendertailed Scorpion
* ***pecos*** - Paruroctonus pecos
* ***silvestrii*** - California Common Scorpion
* ***utahensis*** - Eastern Sand Scorpion
* ***variabilis*** - Paruroctonus variabilis

Genus ***Pseudouroctonus***

* ***apacheanus*** - Pseudouroctonus apacheanus
* ***iviei*** - Pseudouroctonus iviei
* ***minimus*** - Pseudouroctonus minimus
* ***reddelli*** - Texas Cave Scorpion

Genus ***Serradigitus*** - Sawfinger Scorpions

* ***agilis*** - Serradigitus agilis
* ***gertschi*** - Serradigitus gertschi

Genus ***Smeringurus***

* ***mesaensis*** - Giant Sand Scorpion
* ***vachoni*** - Smeringurus vachoni

***vachoni*** - Smeringurus vachoni vachoni
Genus ***Uroctonites***

* ***huachuca*** - Uroctonites huachuca
* ***montereus*** - Uroctonites montereus

Genus ***Uroctonus*** - Forest Scorpions

* ***mordax*** - California Forest Scorpion

Genus ***Vaejovis***

* ***carolinianus*** - Southern Unstriped Scorpion
* ***cashi*** - Vaejovis cashi
* ***coahuilae*** - Lesser Stripetail Scorpion
* ***confusus*** - Yellow Ground Scorpion
* ***crassimanus*** - Vaejovis crassimanus
* ***intermedius*** - Vaejovis intermedius
* ***puritanus*** - Vaejovis puritanus
* ***russelli*** - Vaejovis russelli
* ***sonorae*** - Vaejovis sonorae
* ***vorhiesi*** - Vaejovis vorhiesi
* ***spinigerus*** - Arizona Stripedtail Scorpion
* ***waeringi*** - Vaejovis waeringi
* ***waueri*** - Vaejovis waueri