Scorpions. What is truth and what is wrong.
Scorpions are among the most feared animals. Nevertheless, they are poorly known by people. In this article are presented the most generalized erroneous concepts on them, as well as some of the peculiarities that make them amazing organisms.
Were scorpions the first air-breathing animals on the terrestrial habitats?
If you rely on an old text-book or even on a contemporary source that is not up to date, you could get a wrong answer to this question because despite what such sources claim, most recent discoveries have confirmed that myriapods and some primitive arachnids colonized terrestrial habitats earlier than scorpions.
Scorpions originated during the Silurian time (about 430 millions years BP) in shallow lakes and seas, having an aquatic life. In those habitats they lived together with sea scorpions (Eurypterida), a chelicerate group that is believed has a very close relationship with scorpions. However, scorpions were preceded in the colonization of terrestrial crust by other groups of arthropods: the millipedes (class Diplopoda) and the trigonotarbid spiders (fossil arachnids of the order Trigonotarbida).
Do offspring eat their mother?
Some people believe that offspring kill their mother and eat it. Notwithstanding, it has largely been proved that newly born scorpions (sometime called larvae) are incapable of feeding because in that first instar, chelicerae, pedipalp, and telson are non functional organs. Therefore, newly born scorpions are not able to catch a prey by themselves, or to do feeding activities that involve the use of chelicerae. Scorpions, as other arthropods (v. gr.: insects, crustaceans, centipedes), moult in order to grow. As a result of this physiological activity, they leave an exuvial rest resembling a desiccated scorpion.
On the other hand, when a pregnant female scorpion gives birth, her babies immediately climb on their mother's back, sometimes helped by her.
Perhaps, due to separate observations made by the same person of both phenomena (exuviae and offspring on the mother back), it is thought that the exuviae was what the baby scorpions left after having "sucked" their mother. On the contrary, it has been experimentally demonstrated that female scorpions can give birth several times in a year.
Do scorpions kill themselves when surrounded by fire?
It is a common belief that scorpions commit suicide when they are surrounded by fire, probably due to its dramatic behavior in such extreme situation. During this despicable practice, the scorpion senses that it is being attacked by invisible enemies and then stings all around itself giving the impression that it is self-stinging. However, the correct explanation is that the high temperatures due to the fire cause dehydration and the proteins denaturalization (not reversible over 60 ºC). As a consequence, the scorpion experiences dramatic convulsions, and finally dies.
Experiments in laboratory were carried out some decades ago by the late French arachnologist Max Vachon, and clearly demonstrated that this is the scientific explanation to this phenomenon.
Are scorpions big and very lethal animals?
Because scorpions do not exist in some countries, and are very rare in others, some people are not familiarized with them. In addition, some fantastic literature and films have contributed to create an inappropriate image of these arachnids.
It is known that fossil scorpion Praearcturus gigas
reached one meter in total length, but the longest living species, the Indian Heterometrus swammerdami swammerdami
, reaches less than 30 cm (almost one foot). The largest North American scorpion species is Centruroides gracilis
(a male taken in the Mexican state of Quintana Roo had 145.8 mm in total length).
Other scorpion species are tiny; for example, the Mexican Typhlochactas mitchelli
(male has 8.5 mm in total length, a real world record!). Some small members of the family Buthidae measure between 11 and 20 mm.
Regarding lethal venom, it is present in less than 2% of the almost 1,500 known species. Curiously, the most dangerous species are not the largest ones. For example, the Mexican Centruroides noxius measures 40 to 45 mm in total length; Centruroides suffusus
(Durango’s scorpion), 60–85 mm; and the Brazilian Tityus serrulatus
, 55–70 mm. On the other hand, the very lethal Leiurus quinquestriatus
may reach more than 100 mm (about one-third foot).
Besides, a lot of scorpion species, as those of the family Scorpionidae
, have innocuous venom. I have personally being stung by Mexican and Caribbean members of the subfamily Diplocentrinae
(treated as family Diplocentridae
by some researchers). I only felt a minor pain that compares to the one caused by a fire ant (Solenopsis geminata
), and with no other consequences.
The most dangerous species and their geographical distribution are as follows (in alphabetical order):
- Androctonus australis [AFRICA (Algeria, Egypt, Libya, Sudan?, Tunisia) and ASIA (Israel)]
- Androctonus crassicauda (ASIA: Armenia, Azerbaijan, Bahrain, Egypt, Iran, Iraq, Israel, Jordan, Kuwait, Oman, Saudi Arabia, Syria, Turkey, United Arab Emirates, Yemen)
- Androctonus mauritanicus (Mauritania, Morocco)
- Centruroides elegans (Mexico)
- Centruroides sculpturatus (southwestern USA, northwestern Mexico?)
- Centruroides infamatus (Mexico)
- Centruroides limpidus (Mexico)
- Centruroides meisei (Mexico)
- Centruroides noxius (Mexico)
- Centruroides suffusus (Mexico)
- Leiurus quinquestriatus [AFRICA (Algeria, Chad, Egypt, Ethiopia, Libya, Mali, Niger, Somalia, Sudan, Tunisia) and ASIA (Egypt, Iraq, Israel, Jordan, Kuwait, Lebanon, Oman, Qatar, Saudi Arabia, Syria, Turkey, United Arab Emirates, Yemen)]
- Tityus bahiensis (Brazil)
- Tityus serrulatus (Brazil)
Some interesting records and data
In the book Biology of scorpions appeared a citation from Wilson R. Lourenço in which he recorded the capture of an Andean scorpion Orobothriurus crassimanus at 5,500 m a.s.l., but he later amended this data as 5,550 m a.s.l.
In 1954, J. Baerg recorded a female of the Jamaican striped scorpion Centruroides insulanus that gave birth to 105 babies in a single brood. In 1995, a female of the large scorpion Centruroides margaritatus was found by me in a field of northwestern Nicaragua (Central America) having 104 larvae on her back.
Most scorpions are short-living organisms that live 3 to 5 years as an average, but some species may live almost a quarter of century. According to Gordon’s Scorpion Page
, the Australian Urodacus yashenkoi
could live up to 24 years.
Resistance to submersion in water
Observations in the laboratory have shown that scorpions are capable of long stays under the water. Some Central and North American species of the genus Centruroides resist three to four hours submerged in water without affecting them. The French arachnologist Max Vachon recorded a higher resistance for some African scorpions. This resistance to submersion may be interpreted as adaptation in order to escape from floods.
Resistance to inanition
Scorpions have a low metabolism (i. e., they need few energetic resources). Observations carried out at the laboratory have demonstrated that some species may survive three years without eating anything after the last feeding. This should come as no surprise since most scorpions can tolerate periods of one year without feeding.
These formidable arachnids can also survive until nine months without neither eating nor drinking anything, including water.
Resistance to radiation
Scorpions are among the most resistant animals to the dangerous effects of radiations. In this respect, they go beyond vertebrates, mollusks, spiders, and most insects. It has been experimentally proved that some species are capable of resisting doses of radiation as high as 154,000 roentgens and then survive for at least one month.
Insects, arachnids (including scorpions of the same species and others), myriapods and terrestrial isopods or wood lice are common prey of scorpions, but small vertebrates (lizards, geckoes, snakes, frogs) are not excluded of the diet.
During the difficult drought undergone by the southern territories of Africa in 1970, some scorpions of the species Opistophthalmus carinatus caught terrestrial snails and broke their shells in order to eat the mollusk inside them.
The shortest gestation period (54 days) belongs to the Cuban striped scorpion Centruroides anchorellus.
The longest gestation period (18 months) it is shared by Opisthacanthus asper, Opisthacanthus cayaporum and Urodacus yaschenkoi
Among the arachnids (true spiders, mites, ticks, vinegarroons, whip spiders, pseudoscorpions and other relatives), scorpions are the only ones having:
• Abdomen (= opisthosoma) divided into preabdomen (= mesosoma) and post abdomen (= metasoma)
• A pair of ventral abdominal comb-like appendages: the pectens or pectines
• Telson with two venom glands
• Cuticle containing coumarin, a toxic substance mainly restrict to plants
• Hemolymph containing hemocyanin for oxygen transport
A three-tailed scorpion?
Two-tailed scorpions are known since Pliny “The Elder” times, about 2000 years ago, although several cases were recorded during the last century. Nevertheless, the most anomalous case corresponds to a second instar of Centruroides gracilis that was born with three complete tails and six telsons.
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- ARMAS, L. F. DE. 2001. El alacrán en la cultura cubana contemporánea. Una aproximación. Revista Ibérica de Aracnología 4: 99–103 (abstract available at: http://entomologia.rediris.es/sea/publicaciones/ria/index.htm)
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- BAERG, J. 1954. Regarding the biology of the common Jamaican scorpion. Annals of the Entomological Society of America 47(2): 272–276.
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- FET, V., W. D. Sissom, G. Lowe & M. E. Braunwalder. 2000. Catalog of the scorpions of the world (1758-1998). New York, The New York Entomological Society.
- LAMORAL, B. H. 1971. Predation on terrestrial molluscs by scorpions in the Kalahari Desert. Annals of the Natal Museum 21(1): 17–20.
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- STAHNKE, H. L. 1966. Some aspects of scorpion behavior. Bulletin of the Southern California Academy of Sciences, 65(2): 65–80.
- VACHON, M. 1953. Quelques aspects de la biologie des scorpions. Endeavour 12(46) :80–89.