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April 2005

Feature

 

The button spiders of southern Africa


Ansie Dippenaar-Schoeman

We all know the old saying that dynamite comes in small packages. In the case of spiders, some of the most severe spiderbites come in small packages too - namely the button spiders. In this article Dr Ansie Dippenaar-Schoeman, a spider expert, helps us understand how, why and where these spiders live and what to do should our paths cross in a 'painful' way…

Female button spider

A variety of spiders occur in houses and outbuildings and it is inevitable that they often come into close contact with man. Most spiders will avoid physical contact, but when they are accidentally touched or squeezed, they might deliver a bite in self-defense. All spiders produce venom to kill their prey but only a few species are known to be potentially harmful to humans. The following may influence the action of the venom of the medically important species:

  • The size of the spider and the amount of venom injected. In most cases only a single drop is administered.
  • The part of the body where a person is bitten. A bite near the head is more dangerous than one administered on extremities such as a foot.
  • The age and health of the person bitten. Young children and persons with a medical condition may encounter greater problems.
  • The sensitivity of an individual to the venom. Just as some people are more sensitive to bee stings, the same holds true with respect to spiders.
  • The species of spider that administers the bite. The type of venom differs between species and it is therefore important to positively identify the spider so that the correct treatment can be given.

The venom of the medically important spiders can be divided into those that have neurotoxic (affects the central nervous system) or cytotoxic (affects the tissue around the bite site) venom.

Several spider species produce neurotoxic venom but in southern Africa the button spiders (elsewhere in the world known as widow spiders) are the most important group of medical importance. Six species occur here, belonging to the genus Latrodectus of the family Theridiidae. The button spiders can be divided into the black button spider complex (4 species.) and the brown button spider complex (2 species.).

The button spiders have round abdomens with slender legs of which the third pair of legs is the shortest. Their colour varies from cream to pitch black between species. The markings on the abdomen also vary from stripes to spots. In adult females the markings become less distinct. The patterns on the ventral side of the abdomen vary from having none to one with a distinct red hourglass pattern. Males are much smaller than females and the markings on their abdomen consist of red or white bands.

Female and male button spider

The female constructs her web, which contains a funnel-shape retreat on one side, usually close to the ground in bushes or under debris. The egg sacs are creamy-white and vary in shape from round and smooth to fluffy or spiky.

The female frequently kills the male after mating, hence the common name "widow spiders". The female produces more than one egg sac per season usually during the summer months. The egg sacs are attached with silk to the side of the web. The spiderlings hatch after a week or more and one egg sac can contains more than 100 spiders. They disperse by wind and construct their own webs. They undergo between 7-9 moults before reaching adulthood and can live between 12-18 months. They feed on a variety of insects such as beetles and termites.

Black button female with egg sacs

Brown button female with egg sacs

The black button spider complex contains the following four species: Latrodectus cinctus, L. indistinctus, L. karooensis and L. renivulvatus and they are regarded as the more venomous group. Although no documented records exist of fatality due to black button spider bites, they have the potential to cause severe symptoms with small children and elderly people being at greatest risk.

The black button spiders are black with red patterns on top of the body. The markings vary between species from stripes to spots. In adult females the markings become less distinct. There are no markings on the ventral side of the abdomen in adults. The egg sacs in all four species are creamy-white, round and smooth.

Black button spider egg sac

Zimbabwean button egg sac

The black buttons are widely distributed throughout South Africa and are more often found in natural habitats then in built-up areas. The four black button species have the following distribution pattern:

L. cinctus (east coast button spider) is found in the eastern parts of South Africa (KwaZulu-Natal, Eastern Cape). 

L. cinctus 

L. cinctus distribution

 

L. indistinctus (west coast button spider) is commonly found on the west coast of the Western Cape Province.

L. indistinctus

L. indistinctus distribution

 

L. karooensis (karoo button spider) is a species found only in the karoo.

L. karooensis

L. karooensis distribution


L. renivulvatus (inland button spider) is an inland species found in the central parts of South Africa.

L. renivulvatus

L. renivulvatus distribution

The brown button spider complex contains two species and they are regarded as less venomous: L. geometricus and L. rhodesiensis. They are very similar in appearance to the black buttons but their colour varies from cream, grey and brown to pitch black. The ventral surface of the abdomen in both species has a prominent red to orange hourglass marking, while the dorsal surface is covered with an intricate geometrical pattern in the paler specimens. A potential source of confusion with respect to the identification of these two species is that the most venomous species in Europe and America have the same red hourglass pattern as the two less venomous species found here.
· Latrodectus geometricus is an introduced species and very common in Southern Africa and is usually found in built-up areas, especially around houses and outbuildings. They construct a funnel-shape retreat in dark corners with silk threads radiating outwards. The egg sac is characteristic in having a spiky appearance.

L. geometricus

L. geometricus distribution

· Latrodectus rhodesiensis was originally described from Zimbabwe. They are usually paler in colour and their egg sacs are distinct in being larger and having a more fluffy appearance. They have been recorded from Zimbabwe and also small areas in Gauteng, Mpumalanga and the Limpopo Province

L. rhodesiensis

L. rhodesiensis distribution

Symptoms of Latrodectism: only the female button spider is able to pierce the skin in humans, and in most cases the potential full dosage of venom is not administered. The term latrodectism is used to describe the symptoms and signs caused by envenomation of the button spiders. The black button complex causes a more severe form of envenomation than the brown button spiders.

· Black button spiders: the bite of a black button spider is usually very painful and causes profuse sweating, raised blood pressure and restlessness and generalised muscle pain and cramps, stiffness of the stomach muscles, limb pain especially legs, weakness in legs. Although no documented records exist of fatality due to button spider bites, they have the potential to cause severe symptoms with small children and elderly people being at greatest risk.

· Brown button spiders: the symptoms occurring after a bite from one of the brown buttons are milder and tend to be restricted to the bite site, characterized by a local burning sensation, which may spread to the surrounding tissue and lymph nodes. The bite site is more evident and often seen as a red macular spot or blanched area surrounded by a localised rash. The condition usually clears up within a day or two.

Treatment

In the case of black button envenomation the patient must be hospitalized and vital functions monitored for up to 24 hours. The administration of black button antivenom is the only effective treatment for severe latrodectism. Antivenom (10 ml) is administered intravenously. A follow up dose of 5 ml is occasionally necessary after 4-6 hours. Patients usually respond dramatically within 10-30 minutes. The patient should be kept under observation for at least 6-12 hours after treatment for any allergic reaction (not common) to the refined equine antivenom serum. The only effective agent for the relief of muscular pain and cramps is intravenous calcium gluconate (effect last only 20-30 minutes). Spider bites may easily become infected and care must be taken. The antivenom is produced by the South African Vaccine Producers Institute in Edenvale or can also be obtained from the South African Institute for Medical Research in Johannesburg.


More information:

Dr Ansie Dippenaar-Schoeman is a Specialist Scientist at the ARC-Plant Protection Research Institute, Spider Research Centre, Pretoria DippenaarA@arc.agric.za 

For more information on these venomous spiders the following CD-ROMS and wall poster are available from the Agricultural Research Council (see www.arc.agric.za  Shopping).

Dippenaar-Schoeman, A.S. & Müller, G. 2000. Spiders and scorpions of medical importance in Southern Africa. CD-ROM version 2000.1 ARC-Plant Protection Research Institute, Pretoria.

Dippenaar-Schoeman, A.S. 2002. The Spider Guide of Southern Africa. CD-ROM version 2001.2 ARC-Plant Protection Research Institute, Pretoria.

Dippenaar-Schoeman, A.S. 2003. Venomous spiders of Southern Africa. Plant Protection Research Institute Poster series 2003.1, Agricultural Research Council, Pretoria.

 

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