The Scorpion

Aug 24, 2008 Features / Columnists, Interesting Creatures in Guyana

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Scorpions are eight-legged carnivorous arthropods that are of the order Scorpiones that falls within a class called Arachnida.

There are about 2000 species of scorpions found widely distributed in most parts of the world with the exception of New Zealand and Antarctica.

The body of a scorpion is divided into two parts, the cephalothorax and the abdomen which consists of parts called the mesosoma and the metasoma.

The cephalothorax is also called the prosoma, which is in fact the scorpion’s head comprising the carapace, eyes, chelicerae (mouth parts), pedipalps (claws) and four pairs of walking legs. Its exoskeleton is thick and durable, providing good protection from predators.

As the front half of the abdomen, the mesosoma is made up of six segments with the first segment containing the sexual organs and 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 while the final four segments each contain a pair of book lungs.

A scorpion’s mesosoma is armoured with chitinous plates known as tergites on the upper surface and sternites on the lower surface.

The metasoma on the other hand is the scorpion’s tail which comprises six segments with the first tail segment taking on the appearance of a last mesosoma segment and the last contains the anus and the telson or the sting.

The telson in turn consists of the vesicle which holds a pair of venom glands and the hypodermic aculeus, as well as the venom-injecting barb.

On rare occasions, scorpions are born with two metasomata (tails). However, two-tailed scorpions are not regarded as a different species but merely a genetic abnormality.

Most of these creatures reproduce sexually 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. They are said to possess a complex courtship and mating ritual to effect the transfer.

Mating is said to start with the male and female locating and identifying each other using a mixture of pheromones and vibrational communication once they have satisfied each other that they are of opposite sex and of the correct species.

The courtship starts with the male grasping the female’s pedipalps with his own after which the pair performs a dance. In reality, this movement allows the male to find a suitable place to deposit his spermatophore.

Once the mating is complete the male and female will separate and the male will generally retreat quickly to avoid being cannibalised by the female although sexual cannibalism is not frequent with scorpions.

The young are born one by one 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, as the young are called, cannot survive naturally without the mother since they depend on her for protection and to regulate their moisture levels.

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 eight young.

The young generally resemble their parents and 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 with moulting being 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 and 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.

Scorpions have quite variable lifespans and the actual lifespan of most species is not known. The age range appears to be approximately four to 25 years, with 25 years being the maximum reported life span.

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 behaviour, primarily to evade detection by predators such as birds, centipedes, lizards, mice, possums, and rats.

Scorpions are opportunistic predators of small arthropods and insects. They use their chelae (pincers) to catch the prey initially. 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 a relatively unique style of eating using chelicerae, small claw-like structures that protrude from the mouth that are said to be very unique among arthropods. The chelicerae, which are very sharp, are used to pull small amounts of food off the prey item for digestion.

Scorpions can only digest food in a liquid form and any solid matter (fur, exoskeleton, etc) is disposed of by the scorpion. (Source: The Free Wikipedia Online Encyclopedia)

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