Scorpiones (scorpions)

Life > Eukaryotes > Opisthokonta > Metazoa (animals) > Bilateria > Ecdysozoa > Panarthropoda > Tritocerebra > Arthropoda > Arachnomorpha > Cheliceriformes > Chelicerata > Euchelicerata > Arachnida

Scorpions are ancient animals and fossil records indicate that they were already in existence about 425 – 450 million years ago during the Silurian period and evolved from an amphibious ancestor. They occur in habitats ranging from forest to deserts but it is in the arid areas that they are most common and diverse. Like the insects and spiders, scorpions belong to the phylum Arthropoda and like the spiders they belong to the Arachnida but belong to a different order, Scorpiones.  

Classification

Scorpions are a diverse group of arachnids and include 16 families, 159 genera with 1260 described species worldwide. In southern Africa they fall into two superfamilies and four families: 

Superfamily Scorpionoidea (thin-tail scorpions) - Non-venomous
	Family: Scorpionidae Found in Africa and Asia, with a total of 4 genera. Opistophthalmus the only southern African genus and includes 59 described species with 17 new species in preparation for publication. While the sting can be painful and some species (e.g. Opistophthalmus glabrifrons) are reported to have some unpleasant systemic symptoms, the venom of this group is of little medical importance.
	Family: Liochelidae Includes the genera Opisthacanthus, Hadogenes and Cheloctonus These scorpions and are not venomous to people. With the Scorpionidae, they belong to the group commonly referred to as the thin-tail scorpions and a sting from one of them should, at worst, be no more than a bee sting. This family was previously a subfamily of the Scorpionidae. It is distributed through Africa, south-east Asia, Australia and South America and its associated islands.
	Family: Bothriuridae The bothriurids are Gondwanaland relics and include 10 genera in South America, 1 in Australia and the endemic northern Namibian genus Lisposoma that includes 2 species. Lisposoma scorpions are small (18 to 32 mm body length) with a relatively thick tail. The chelae in males are only slightly thicker than the tail. These scorpions can be confused with smaller buthids but tails of the latter are considerably thicker than the chelae.
Superfamily: Buthoidea (thick-tail scorpions) - Highly venomous
	Family: Buthidae The buthids are commonly referred to as the thick-tailed scorpions and are generally venomous to people, the most venomous genera being Parabuthus and Buthotus. This is a large and widespread family with over 500 species occurring on all continents except Antarctica. Seven genera occur in southern Africa

Habits and behaviour

Scorpions are mostly nocturnal and they hunt insects, other arachnids and small reptiles and mammals. During the day they can be found under rocks, bark, cow-pats and rock crevices.

Often they are attracted to insect activity around lights and many queries received by the Museum relate to this. Many people leave lights on during the night and these attract insects that in turn attract the scorpions.

When aggravated, scorpions seem to make a hissing sound. This sound is produced differently by differently scorpions. One species scrapes its sting along a granulated area on the upper surface of the first two segments os the tale while another vibrates its pincers together.

Prey capture

Scorpions either ambush unsuspecting prey that wander close to their retreats, or they wander about actively hunting for prey. They detect prey by air movement over the trichobothria (long sensory setae) and when the tarsal sense organs detect the prey, within about 150 mm, this induces a dash to capture the prey. The prey is caught with the chelae. Buthids, the thick tail scorpions, have strong venom and small chelae so they sting almost instantly killing their prey and therefore do not require large chelae to hold onto prey. Other, non buthid species, the thin tail scorpions, have weak venoms but have large powerful chelae that enable them to either secure the prey until it dies from the sting, or to simply crush the prey. The prey is orientated specifically and is eaten head first. Scorpions do not eat every day and even if conditions are ideal, that is warm, windless nights, only a small percentage will feed. Some scorpions can survive 6 to 12 months without food. Prey includes insects, centipedes, millipedes, snails, spiders, soifugids, scorpions and even small reptiles and mice.

Scorpion reproduction and development

In most species (not all) the male initiates the courting. He grips the female pedipalps (chelae) and leads her in a mating dance that usually lasts about 30 to 60 minutes, but can vary from 5 minutes to 2 days and they can cover a distance of about 25 metres. Once a suitable substrate is found, the male deposits a spermatophore from his genital aperture and the female is then guided over the spermatophore that is taken up into her genital opercula. The sperm uptake lasts from a few seconds to 6 minutes.

Opistophthalmus capensis female with young. [photo N. Larsen ©]

Scorpions are viviparous (carry the eggs inside the reproductive tract and give birth to live young). After a 3 to 18 month gestation period, 1-105 live young are born, the average numbering approximately 26. The female, in most species, forms a basket with her first or first and second pairs of legs to catch the newborn at birth. They then climb up her legs onto her back where they will moult for the first time. The birthing rate varies from 1 per minute to 1 per hour and can continue from 12 hours to 10 days depending on the species. The young disperse after 3 to 14 days before they become a meal for their own mother. Food supply and temperature seems to influence the litter size  and gestation period and the latter can double in cold conditions. Embryos are reabsorbed if there is a lack of food. 

Scorpions moult 6 times before maturity and that varies from 6 months to 8 years. Their life expectancy varies with the different species and ranges from 2 years to as much as 10 to 25 years.

Acknowledgements

Thanks to Lorenzo Prendini for his enthusiasm and assistance in producing this site and for the numerous unpublished papers made available. Thanks also to Drs Nils Bergman, Gerbus Muller and Ansie Dippenaar-Schoeman for permission to include information from several of their publications.

Publications

• Bergman, N. J. 1997. Scorpion sting in Zimbabwe. South African Medical Journal 87: 163-167.

• Bergman, N. J. 1997. Clinical description of Parabuthus transvaalicus scorpionism in Zimbabwe. Toxicon 35: 759-771.

• Croucamp, W. 2000. Scorpion stings - diagnosis and management. The rule of thumb to determine the danger level of a sting is explained. Journal of Continued Medical Education 18(8): 680-682.

• Dippenaar-Schoeman, A. and Müller, G. 2000. Medically important spiders and scorpions of southern Africa. (CD-Rom). Agricultural Research Council, Pretoria. 

• Eastwood, E. B. 1977. Notes on the scorpion fauna of the Cape. Part 1. Descriptions of neotypes of Opisthophthalmus capensis (Herbst) and remarks on O. capensis and O. grandifrons Pocock, species group (Arachnida, Scorpionida, Scorpionidae). Annals of the South African Museum 72: 211-226.

• Eastwood, E. B. 1977. Notes on the scorpion fauna of the Cape. Part 2. The Parabuthus capensis (Ehrenberg) species -group; remarks on taxonomy and bionomics (Arachnida, Scorpionida, Buthidae). Annals of the South African Museum 73: 199-214.

• Eastwood, E. B. 1978. Notes on the scorpion fauna of the Cape. Part 3. Some observations on the distribution and biology of scorpions on Table Mountain. Annals of the South African Museum 74: 229-248.

• Eastwood, E. B. 1978. Notes on the scorpion fauna of the Cape. Part 4. The burrowing activities of some scorpionids and buthids (Arachnida, Scorionida). Annals of the South African Museum 74: 249-255.

• Filmer, M. R. and Newlands, G. 1994. Araneism and Scorpionism in Africa south of the equator. Part 2 Scorpionism. Diseases of the Skin 8(2): 7-10.
• Harrington, A. 1982. Diurnalism in Parabuthus villosus (Peters) (Scorpiones, Buthidae). Journal of Archnology 10: 86.
• Lamoral, B. H. 1979. The scorpions of Namibia (Arachnida: Scorpionida). Annals of the Natal Museum 23: 497-784.
• Lawrence, R. F. 1955. Solifugae, Scopiones and Pedipalpi, with checklists and keys to South African families, genera and species. Results of the Lund University Expedition in 1950-1951. In B. Hanström, P. Brinck & G. Redebeck (Eds) South African Animal Life 1: 152-262. Uppsala: Almqvist & Wiksells.
• Leeming, J. 2003. Scorpions of Southern Africa. Struik Publishers, Cape Town.
• Müller, G. J. 1993. Scorpionism in South Africa. A report of 42 serious scorpion envenomations. South African Medical Journal 83: 405-411.
• Newlands, G. 1972. Ecological adaptions of Kruger National Park scorpionids (Arachnida: Scorpionides). Koedoe 15: 37-82.
• Newlands, G. and de Meillon, E. 1987. Venomous Creatures. Struik Pocket Guides for southern Africa. Struik, Cape Town.
• Newlands, G. 1985. A re-appraisal of the Rock scorpions (Scorpionidae: Hadogenes). Koedoe 28: 35-45.
• Newlands, G. Scorpion Defence Behaviour. African Wildlife 23: 147-153.
• Paalini, A. 1995. Treatment of Bites and Stings. Kagiso Publishers.   
• Polis, G.A. (editor) 1990.The Biology of Scorpions. Stanford University Press, Stanford, California.
• Prendini, L. 2000. A new species of Parabuthus Pocock (Scorpiones: Buthidae), and new records of Parabuthus capensis (Ehrenberg), from Namibia and South Africa. Cimbebasia 16: 201-214.
• Prendini, L. 2000. Phylogeny and classification of the superfamily Scorpionoidea Latreille 1802 (Chelicerata, Scorpiones): An exemplar approach. Cladistics 16: 1-78.
• Prendini, L. (in press). Phylogeny of Parabuthus (Scorpiones, Buthidae). Zoologica Scripta.
• Prendini, L. (in press). Substratum - specificity and speciation in southern African scorpions: Urba's "effect hypothesis" revisited.
• Prendini, L. (in press). Two new species of Hadogenes (Scorpiones, Ischnuridae) from South Africa, with a redescription of Hadogenes bicolor and a discussion on the phylogenetic position of Hadogenes. Journal of Arachnology.
• Prins, A. and Leroux, V. 1990. South African Spiders and Scorpions. Anubis Press, Cape Town.
• Shire, L., Muller, G.J. and Pantanowitz, L. 1996. The diagnosis and treatment of envenomation in South Africa. Journal of the South Africa Institute for Medical Research  :32-35.

Text and images by Norman Larsen ©.