Scorpions
Scorpions are fascinating arachnids belonging to the class Arachnida and the order Scorpiones. They have a long evolutionary history, with ancestors dating back over 400 million years. Found on every continent except Antarctica, scorpions thrive in various habitats, including arid deserts, tropical jungles, and temperate forests. Typically nocturnal, these creatures possess a unique anatomy, featuring eight legs, clawed pedipalps for capturing prey, and a segmented body with a characteristic stinging tail. Their diet is carnivorous, and they primarily feed on liquidized prey, aided by their specialized mouthparts.
Reproductive strategies vary significantly among scorpion species, with gestation periods ranging from 1.5 to 18 months. Mating involves a courtship dance where males present spermatophore sacs to females. After birth, juvenile scorpions often stay on their mother's back until their first molt. Interestingly, scorpions exhibit fluorescence under ultraviolet light, appearing light green, which may aid in their detection by humans and predators. With lifespans varying from three to fifteen years depending on the species, scorpions continue to intrigue scientists and enthusiasts alike.
Scorpions
Scorpion Facts
Classification:
Kingdom: Animalia
Subkingdom: Bilateria
Phylum: Arthropoda
Subphylum: Chelicerata
Class: Arachnida
Order: Scorpiones
Families: Beliseriidae, Bothriuridae, Buthidae, Caraboctonidae, Chactidae, Chaerilidae, Diplocentridae, Euscorpiidae, Hadruridae, Hormuridae, Ischnuridae, Iuridae, Pseudochactidae, Scorpionidae, Typhlochactidae, Vaejovidae, and other families
Geographical location: Every continent except Antarctica
Habitat: Strictly terrestrial, found in both arid and tropical regions
Gestational period: Varies among species; lengths of between 1.5 and eighteen months have been reported
Lifespan: Depending on the species, the lifespan may be between three and five years, while other scorpions are known to live for between ten and fifteen years
Special anatomy: Eight legs, chelicerae mouthparts and simple eyes like other arachnids; clawed pedipalps for grasping prey; telson with a sting that can deliver venom; special sensory organs, called pectines, that act in an olfactory capacity
Scorpions are members of the phylum Arthropoda, and more specifically of a subphylum of that taxon known as Chelicerata. Scorpions are members of the class Arachnida, those arthropods having eight legs and chelicerae mouthparts, and lacking antennae. Scorpions are the oldest arthropod terrestrial group, whose aquatic ancestry dates to Silurian, times over 400 million years ago. Their terrestrial invasion occurred in the Devonian period.
Scorpions are cosmopolitan in distribution, occurring on all continents except Antarctica. Although most people envision scorpions as desert creatures, scorpions are found in the tropical jungles, temperate forests, savannas, and in high elevations on mountains. They are mostly nocturnal creatures, as they have little defense against the ultraviolet radiation of the sun. They are quite variable in size: Some are as small as 12 millimeters, while others (the South African rock scorpion, Hadogenes troglodytes) range up to 23 centimeters in length like the giant forest scorpion (Gigantometrus swammerdami).
Scorpion Physiology
Scorpions are segmental in form—their body is divided into an anterior prosoma and a segmented abdomen. A one-piece carapace covers the prosoma. The abdomen is divided into a preabdomen of seven segments and a postabdomen of five segments, ending in a stinging apparatus. The pedipalps are pincerlike and are used to capture and hold prey. The chelicerae are pincerlike as well and are used to macerate the prey. There are four pairs of walking legs, all ending in a pair of claws. All scorpions are carnivorous and are essentially liquid feeders. Copious amounts of digestive enzymes are poured over macerated areas of the prey, and the liquid is then pumped into the stomach.
Scorpions are well-equipped with sensory structures. They have a pair of simple eyes located in the center of the carapace. Additionally, there are from two to five pairs of eyes located along the anterior and lateral margins of the carapace. Scorpions have many setae or sensory hairs located over the dorsal surfaces of the body. These hairs function to pick up vibrations and air movement and are used to detect prey. The hairs are large on the pedipalps and are called trichobothria. Unique to scorpions is a pair of ventrally located, comblike appendages called pectines. These structures are mainly chemoreceptors and are used to pick up pheromone trails of insects. Pectines are also used to dig burrows, although the legs mainly perform this function.
Scorpions breathe by means of book lungs that are ventrally located and open to the outside via a pair of spiracles. In this way, the book lungs are kept moist for oxygen diffusion. A circulatory system is present, with a dorsally situated heart that opens via ostia or pores into the hemocoels and book lungs. Scorpions are also well-equipped to deal with excretory wastes, using Malpighian tubules. These tubules filter nitrogenous wastes from the hemocoels and deposit the waste into the gut tube for elimination.
Mating and Reproductive Strategies
There are separate sexes, and the gonads are tubular in construction in both sexes. The gonopore opens on the ventral surface of the mesosoma. Males lay a spermatophore sac that is picked up by the female during a courtship dance. This dance is initiated by the male, who grasps the female’s pedipalps in his and dances back and forth in a face-to-face position. When the female touches the opening lever of the spermatophore, sperm are released. Fertilization is internal, as is the development. Scorpions are either ovoviviparous or viviparous. The time from conception to birth in scorpions is quite variable. In some groups, birth requires only 1.5 months’ gestation, while in others, the gestation period can last up to eighteen months. In viviparous species, the embryo is fed via a tube that extends from the digestive caeca to the embryos living in the ovarian tubes. The juvenile scorpions will exit the mother via the gonopore and climb atop her back, where they will mature and go through a molt. After this first molt, they will take up their own independent existence. Scorpions will molt from four to seven times before they reach the adult stage. As an adult, no molting occurs, and limbs lost during life are not regenerated.
Scorpion Fluorescence
Looking for scorpions is made easy by the fact that scorpions will fluoresce under an ultraviolet black lamp. Scorpions appear light green under ultraviolet radiation. Fluorescence may be caused in part by chemicals known as carotenoids that are found in the epicuticle.
Principal Terms
Aculeus: The sting, either a single or double hollow barb that delivers the venom to prey
Exoskeleton: An external, jointed skeleton made up of chitin and protein
Oval Gland: The poison gland in the scorpion telson
Ovarian Diverticulum: Used to house embryos and to obtain nutrients via absorptive cells among viviparous species
Pectines: Comblike structures on the ventral surface of the scorpion that are used in chemoreception
Pedipalps: Clawlike appendages that are used to catch and hold prey
Bibliography
Brusca, R. C., and G. J. Brusca. Invertebrates. 4th ed., Sinauer Associates, 2023.
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Gaban, D. "Androctonus australis (L.) Fattailed Scorpion." Forum of the American Tarantula Society, vol. 6, no. 2, 1997, pp. 52-53.
"The Mystery behind a Scorpion's Glow." Australian Geographic, 3 July 2017, www.australiangeographic.com.au/topics/wildlife/2017/07/the-mystery-behind-a-scorpions-glow. Accessed 21 Aug. 2024.
Polis, G. A., editor. The Biology of Scorpions. Stanford University Press, 1990.
"Scorpion." San Diego Zoo Animals & Plants, animals.sandiegozoo.org/animals/scorpion. Accessed 21 Aug. 2024.
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