Characteristics of scorpions, habitat, reproduction and feeding

661
Alexander Pearson

The scorpions or scorpions are a group of arthropod animals that belong to arachnids. They are characterized mainly by presenting an extension at the end of their abdomen that ends in a poison inoculating stinger. This order was first described in the 19th century by the German entomologist Carl Koch and is made up of approximately 1,400 species..

These animals have long been feared because they synthesize some of nature's most toxic and powerful poisons. However, in most cases they are unlikely to attack humans if left unmolested..

Scorpion. Source: Pixabay.com

Article index

  • 1 Taxonomy
  • 2 Features
  • 3 Morphology
    • 3.1 - Prosoma
    • 3.2 - Opistosome
    • 3.3 - Internal anatomy
  • 4 Habitat and distribution
  • 5 Classification
  • 6 Food
  • 7 Playback
  • 8 Representative species
    • 8.1 Androctonus crasicauda
    • 8.2 Leiurus quiquestriatus
    • 8.3 Parabuthus transvaalicus
    • 8.4 Centruroides exilicauda
  • 9 References

Taxonomy

The taxonomic classification of scorpions is as follows:

Domain: Eukaryota

Animalia Kingdom

Phylum: Arthropoda

Subphylum: Chelicerata

Class: Arachnida

Order: Scorpiones

Characteristics

Scorpions are considered multicellular eukaryotic organisms. In their cells they present an organelle called the cell nucleus, in which the animal's DNA is packaged, forming the chromosomes. In addition, they are made up of different types of cells that fulfill various specific functions.

Scorpions are triblastic animals, because during their embryonic development they present the three germ layers: ectoderm, mesoderm and endoderm. From them, the different tissues that will make up the adult animal are formed, with their specifications regarding functionality..

These animals belong to the group of organisms that present bilateral symmetry. This is explained because when an imaginary line is drawn along the longitudinal axis of the animal, two exactly equal halves are obtained from it..

One of the most interesting characteristics of scorpions is that they fluoresce. That is, when subjected to ultraviolet light, scorpions glow.

This is due to some chemical compounds that they have in their exoskeleton: 7-hydroxy-4-methylcoumarin and ß-carboline. This feature has been very useful, especially to locate them in dark places for study.

Fluorescence of scorpions. Source: Pixabay.com

Morphology

Taking into account that scorpions belong to the phylum Arthropoda, it is correct to affirm that they have a body divided into two very well differentiated sections: the prosoma (also known as cephalothorax) and the opistosoma or abdomen..

Regarding the size, this varies depending on the species. There are scorpions so small that they only measure 8 mm, while there are other more robust ones that can measure up to 25 cm.

Likewise, scorpions have varied colors, having dark colors such as black or brown, even going through yellow or cream specimens..

- Prosoma

It is the anterior segment of the animal. It is covered by a kind of shell that is known as the prosomic shield. The texture of this can vary according to the species. This is how it can be rough, smooth, grainy or even have combined regions.

On the dorsal surface of the prosoma are the eyes distributed as follows: a pair in the middle and in the anterolateral region the lateral eyes. The number of eyes is variable. There are species that do not have lateral eyes, as well as other species that can have up to five pairs of eyes..

The ventral surface of the prosoma is almost entirely occupied by the coxae of the articulated appendages and by the sternum..

From the prosoma all the articulated appendages of the animal originate: two chelicerae, two pedipalps and eight legs. All these are distributed in pairs.

Cheliceros

They constitute the first pair of appendages of the animal. They are short in length, but they make up for this with the robustness of their build. They are shaped like a forceps and are located on both sides of the oral opening.

Each chelicerae is made up of three pieces. The clamp-shaped structure that has the distal end of the chelicerae is made up of a so-called fixed finger and another of the mobile type..

Likewise, chelicerae may present certain structures such as silks that fulfill sensory functions..

Pedipalps

They constitute one of the most representative anatomical structures of these animals. They are the second pair of jointed appendages that emerge from the prosoma.

They are made up of a total of six knuckles: tarsus, tibia, patella, femur, trochanter, and coxa. It is important to note that not all the knuckles have the same thickness. The tibia is noticeably thickened. The tarsus, together with the terminal end of the tibia, forms the clamp of the pedipalps.

Terminal forceps are very useful for scorpions, since they use them to capture prey and even tear them.

The pedipalps of scorpions also fulfill sensory functions, since they are practically covered with sensory receptors that allow them to perceive and capture signals from the external environment..

Legs

Scorpions have four pairs of legs. These are distributed directly from the prosoma.

They are made up of seven pieces. From the distal to the proximal are the following: telotarso, basitarso, tibia, patella, femur, trochanter and coxa. The first legs are short and this is increasing in the rest of the pairs.

The terminal segment of the legs (telotarso) has certain extensions of different texture, which depending on the species can be bristles and even spines. It also has two nails.

Although it is established that the main function of the legs is the locomotion of the animal, these also fulfill other functions such as digging the ground, to mate or during the time of the birth of the young.

Specimen of Centruroides infamatus. Here their pedipalps, prosoma, mesosome, and metasoma are clearly seen. Source: Tomas Castelazo [CC BY-SA 3.0 (https://creativecommons.org/licenses/by-sa/3.0)]

- Opistosome

The opistosoma of scorpions has the peculiarity that it is divided into two areas: the metasoma or tail and the mesosoma or abdomen.

Mesosome

It is wide and is divided into seven segments. Most of the systems that make up the animal are contained in it..

It has some very important structures, such as the genital opening, which is where the ducts of the male and female genital apparatus lead. Likewise, it presents respiratory spiracles, specifically between segments 3 and 6.

In the mesosome, at the level of the second segment, there is a pectinal basal plate, in which sensory organs that are known as combs originate. These are found only in individuals of the order Scorpiones.

They are articulated mobile structures that are made up of three sheets. They also have teeth that vary in size and quantity according to the species.

Combs have sensory function, specifically as mechanoreceptors and chemoreceptors.

Metasome

It is a characteristic and distinctive trait of scorpions. In general, this anatomical structure is called the tail. However, it is nothing more than a prolongation of the opistosome..

It is made up of five segments. The terminal end is known as telson and is the one that contains the gland that synthesizes poison, in addition to the stinger with which it inoculates.

- Internal anatomy

Respiratory system

Scorpions have a respiratory system similar to that of other arachnids. This consists of a combination of tubes called tracheas. These reach organs known as book lungs. They are made up of a series of tegumentary invaginations, which are stacked one on top of the other, giving the appearance of the pages of a book..

The tracheas open to the outside through holes called spiracles, which allow the entry and exit of air. It is at the level of the book lungs that gas exchange takes place.

Nervous system

The nervous system of scorpions is of the ganglionic type. It is made up of ganglia that are made up of neuronal clusters.

The main element of the nervous system is a brain that is located around the esophagus. It is made up of two ganglia.

It also has a ventral ganglion that is divided into seven nodes. This emits nerve fibers to the different muscles of the animal.

Digestive system

Scorpions have a complete digestive system, with an entrance hole and an exit hole.

In the first place, it presents an oral cavity, which has chelicerae on its edges. It has two intestines, one front and one middle, in which the absorption of nutrients is carried out.

The terminal segment is the anus, through which the waste products of digestion are released.

It is important to mention that the digestive system of scorpions has a series of attached glands that synthesize and release digestive enzymes such as amylase, lipase and protease. These have the function of degrading the different ingested nutrients (fats, proteins and carbohydrates).

Circulatory system

The circulatory system of scorpions is almost entirely open. The circulating fluid, blood or hemolymph, does so through blood sinuses that are found in the different tissues that make up the animal.

Likewise, it has a kind of cylindrical structure, similar to a tube that has a dorsal position, also presenting a heart that has about seven ostioles. From this an aorta artery arises, which contributes to the distribution of blood fluid to every corner of the body..

Excretory system

Scorpions have the same excretory system as the rest of the arachnids. This is made up of tubular structures called Malpighi tubes that open at the level of the terminal portion of the intestine..

Reproductive system

Scorpions are dioecious, which means that the sexes are separate. The sex glands or gonads are represented by tube-like ducts that are grouped in pairs. Sex cells are produced in them: sperm in males and eggs in females..

Habitat and distribution

Scorpions are widely distributed throughout the planet, with the exception of the North Pole and Antarctica. 

They are particularly abundant and diverse in the tropical and subtropical region of the planet. Scorpions have managed to colonize a wide range of ecosystems such as deserts, savannas, jungles and forests. In the case of forests, they can be found in caves, buried in the ground or even on the branches of trees..

Scorpion specimen in its natural habitat. Source: Pixabay.com

The place on the planet where scorpions are most diverse is in the desert areas of Mexico. The scorpion that presents the deadliest poison in the world, the Androctonus australis, It is located in the north of the African continent and in Southwest Asia.

Classification

The order Scorpiones is made up of about 15 families.

- Microcharmidae: with a total of 15 species.

- Buthida: it is the most diverse family, with more than 90 species.

- Euscorpiidae: they are characterized by having very well developed pedipalps. They comprise approximately 58 species.

- Vaejovidae: its characteristic element is a keel that runs along its longitudinal axis.

- Urodacidae: it is endemic to the Australian continent. It only comprises two species.

- Bothriuridae: comprises a total of 151 species on average.

- Chaerilidae: encompasses 20 species that are only found in southern Asia. They present colors that cover various ranges of brown.

- Hemiscorpiidae: It is made up of large specimens that can reach up to 20 cm in length. Your metasoma tends to be very thin and disproportionate to your body.

- Heteroscorpionidae: it is made up only of endemic species of the island of Madagascar.

- Luridae: are located mainly in Greece, although specimens have also been collected in Turkey.

- Scorpionidae: includes large species, being able to measure up to 25 centimeters.

- Caraboctonidae: are characterized by presenting a large number of sensory receptors in the form of hairs.

- Chactidae: feature a fairingless exoskeleton, plus a hexagonal-shaped sternum.

- Pseudochactidae: It comprises a single species and is characterized by having a delicate and elongated body.

- Superstitioniidae: They are native to the north of the American continent and comprise a total of ten species. They are dark colored scorpions that are also characterized by their robustness.

Feeding

The eating habits of scorpions are mainly carnivorous. Scorpion species are very effective predators, thanks to the power of their pedipalps and the toxicity of their venom.

Scorpions' diet is based on small invertebrates, mainly other arachnids, including other scorpions. They can also feed on small mollusks and some vertebrates such as certain reptiles and rodents..

The time of day when scorpions tend to hunt their prey is at night.

Scorpions can perceive potential prey through an organ called the trichobotary, which allows them to pick up slight movements around them. Once it has identified its prey, making use of its pedipalps to capture it. Its claws are quite powerful and it keeps the prey immobile.

Then, with the help of chelicerae, it begins to tear the prey to pieces and also injects the various digestive enzymes to start digestion. If necessary, the animal makes use of its tail and inoculates its prey with venom..

After digestive enzymes have processed the prey to a certain extent and it is predigested, the animal ingests it to begin the internal digestion process..

Inside the body of the scorpion, the food is subjected to the action of the various digestive enzymes and is further degraded. At the level of the intestine, the absorption of nutrients is carried out and the waste is expelled through the anal orifice.

It is important to note that in scorpions, nutrients that are not used immediately by the animal's cells are stored in the form of glycogen..

Reproduction

Female scorpion carrying her young. Source: Fusion121 at English Wikipedia [Public domain]
Scorpions reproduce sexually, which requires the union of a male sexual gamete (sperm) and a female (egg)..

The reproduction process of scorpions is one of the most colorful and complex in the animal kingdom, since it involves a rather interesting courtship ritual.

In some species, females release chemicals known as pheromones into the environment, which have the function of attracting a male specimen that is nearby..

When the male approaches, he begins to perform various striking movements, in order to attract the attention of the female. Once it is captured, they link through the clamps of their pedipalps and begin to make an oscillatory movement that goes back and forth. This is known as the courtship dance of the scorpions..

The purpose of this dance is to place the female in the most suitable place so that the spermatophore can enter her body correctly. Once it has been introduced into the female, the fertilization process occurs. 

The fertilized eggs that are generated develop in the uterus and when a reasonable time has elapsed (up to 12 months), the young are born. This means that they are viviparous..

Scorpions that are born are very small and white in color. These climb towards the mother's back and remain there for a time, until they undergo a first molting process..

Eventually they descend and are able to fend for themselves. Then it continues its development, undergoing other processes of molting. They reach sexual maturity after about two or three years.

Representative species

The order Scorpiones encompasses a total of 1,400 species. Of these there are some that stand out, mainly due to the toxicity of their venom.

Androctonus crasicauda

He hails from North Africa and the Middle East. Because of this, it is known as the short-tailed Arabian scorpion..

It is typically black in color, although brown and even reddish specimens have been recorded. Likewise, its metasoma or tail has a robust appearance and culminates in a prominent stinger..

The toxin it synthesizes is very powerful and life threatening, even for humans.

Androctonus crassicauda. Source: Per-Anders Olsson [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0/)]

Leiurus quiquestriatus

Also known as the yellow Palestinian scorpion, it is found primarily in the desert environments of North Africa and southern West Africa..

It is one of the most poisonous scorpions in the world, since the toxicity of its venom is neurotoxic. Presents cardiotoxins that directly affect the functioning of the heart muscle.

Parabuthus transvaalicus

It is known as the Transvaal thick-tailed scorpion. It can reach up to 16 cm in length. It is located mainly in the desert areas of the south of the African continent.

It is considered one of the most poisonous scorpions in Africa, as it is capable of producing up to 14 milligrams of venom and spraying or inoculating it on its prey.

Centruroides exilicauda

It is commonly known as the Sonoran desert scorpion or Baja California bark scorpion..

During the 1940s, 1950s and 1960s, a large number of deaths were attributed to him as a result of his bite. This has radically changed, with few deaths it can cause because medicine has achieved a powerful antidote.

References

  1. Acosta, L. (2005). Scorpions - Scorpions or scorpions. Chapter of the book "Arthropods of medical interest in Argentina". Mundo Sano Foundation.
  2. Brusca, R. C. & Brusca, G. J., (2005). Invertebrates, 2nd edition. McGraw-Hill-Interamericana, Madrid.
  3. Curtis, H., Barnes, S., Schneck, A. and Massarini, A. (2008). Biology. Editorial Médica Panamericana. 7th edition.
  4. De la Fuente, J. A. (1994). Phylum Chelicerata. Pp. 126-159, in Arthropod Zoology. Interamerican.
  5. McGraw-Hill. Diplopoda: pp. 300-313.
  6. Hickman, C. P., Roberts, L. S., Larson, A., Ober, W. C., & Garrison, C. (2001). Integrated principles of zoology (Vol. 15). McGraw-Hill.
  7. Polis, G. (1990) The biology of Scorpions. Stanford University Press. Stanford_California.
  8. Teruel, R. and Melic, A. (2015). Order Scorpiones. IDEA-SEA Magazine. 18.

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