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November 2002

Feature

 


The baboon spiders of South Africa

by Dr Ansie Dippenaar-Schoeman

Baboon spiderBaboon spiders or tarantulas, as they are known outside Africa, are the giants of the spider world. The last two leg segments resemble the finger of a baboon hence, the common name, baboon spiders. The first South African spider known from literature was a baboon spider mentioned in 1702 by Petiver. More than a hundred years later in 1832 the first baboon spider Mygale atra was described from South Africa and only in 1871 the first genus Harpactira was established for Southern African baboon spiders.

The last two segments resembles the finger of a baboon, hence this spider's common name.The study of the Southern African baboon spiders form part of the South African National Survey of Arachnida (SANSA). SANSA was initiated in 1997 by the ARC-Plant Protection Research Institute's Spider Research Centre in Pretoria. One of the main aims of SANSA is to make an inventory of the Arachnida fauna of South Africa. An inventory of our present knowledge of the baboon spiders of Southern Africa was recently completed resulting in the publication of an identification manual of the baboon spiders of this region (Dippenaar-Schoeman, 2002). This data was also incorporated into the BioBASE project of the Mpumalanga Parks Board, the GAP project of Gauteng Nature Conservation and ISIS-2000. No red data information is yet available of the group. (Red data information gives an indication of a species population status - for example whether it is endangered or critically endangered)

Southern Africa has a rich fauna of baboon spiders, represented by seven genera and 42 species. They belong to the family Theraphosidae, a very diverse family, represented by 86 genera and about 612 species worldwide. The theraphosids have a pantropical distribution and are known from Africa, the Far East, Australia as well as parts of South, Central and North America.

Typical markings on a baboon spiderThe baboon spiders are large, with a body size varying from 13-90 mm. They are very hairy and their colour varies between hues of brown, grey, yellow to black. The carapace is frequently decorated with radiating bands while the abdomen has variegated markings. They are easily recognized by their large size, strong, hairy bodies, and the They are easily recognised by the thick pad of hair on the last two segmentsthick pad of hair present ventrally on the last two leg segments.

The baboon spiders are ground living animals and construct silk-lined burrows (Fig. 5) or retreats under stones and rocks. They use their chelicerae, fangs and pedipalps to excavate the burrows. They are found in a variety of habitats such as dry acacia scrubland, grassland or savanna woodland. In arid regions their burrows are usually deep to provide them protection from high temperatures. They are predominantly nocturnal sit-and-wait hunters and The baboon spiders are ground living animals and construct silk-lined burrows.most species await the approach of prey within the entrance of their burrows. Usually the silk lining extends past the entrance to form a silk rim that sometimes incorporates pieces of plant material. The silk threads warn the spider of approaching prey. Prey is usually captured at or near the retreat entrance. Presumably they rely on sensory detection systems consisting of special setae (trichobothria) to detect air currents generated by moving prey or soil- and The silk threads warn the spider of approaching prey.silk vibration detectors such as the slit sensilla or club-shaped trichobothria. They hide in their burrows during the day and the entrances are frequently silked over during daylight hours by a thin, transparent cover. The tarsal claws of the first and second legs and palp maintain contact with the silk encircling the burrow entrance. Prey are ambushed and dragged into the burrow. When they wander outside the burrow entrance, draglines of silk are usually left on the soil surface.

Before mating the male transfers sperm from the genital opening under the abdomen, to the secondary sexual organs on the pedipalps Mating usually takes place in spring and summer. Before mating the male transfers sperm from the genital opening under the abdomen, to the secondary sexual organs on the pedipalps. This is done by depositing sperm on a small sperm web. The sperm is then absorbed with the palpal organ, where it is stored until mating. At this stage adult males usually change their life-style completely to become wanderers in search of females. Sexual dimorphism occurs with the male being smaller than the female. To ensure recognition by the female, the male uses various techniques to approach the female. In some species the male reveals his presence, by tapping rhythmically against the sides of the burrow. Courtship in most baboon spiders is usually of short duration. If a mating spur is present on the front leg of the male it is used to force open the fangs of the female. This prevents her from attacking.

Eggs are usually laid during summer and this process does not necessarily take place directly after mating. In the horned baboon spiders the female sometimes only lays eggs five months after mating. The number of eggs produced by the different spider genera varies greatly. Eggs are usually deposited in a waterproof egg sac made of silk and deposited in the bottom of the burrow. The female tends the eggs and young. Newly hatched spiderlings are not always mobile after hatching. The spiderlings of the horned baboon spider only commence moving about 50 days after hatching. In some genera the young spiders stay with the mother for an extended period of time.

As young spiders grow they undergo a number of moults. The first moult already takes place in the egg sac. A few days before moulting commences, the spider stops eating. First the skin tears under the carapace just above the coxae of the legs. The carapace then lifts off like a lid but remains attached at the pedicel. Next, the skin of the abdomen tears at the side and the abdomen is freed. The legs, pedipalps and chelicerae are pulled free from the skin with rhythmic movements until finally the spider pulls free. At this stage the spider is soft and defenseless. The new skin hardens after a while. In young spiders, moulting is completed within a few minutes but as the spider matures the process may last for an hour or more. Males usually moult fewer times than females. In the baboon spiders a female can also moult after reaching maturity. If a leg is lost between moults, the spider is capable of regenerating a new one, which appears after the next moult. Initially, the new leg is shorter and thinner than the others are.

As a large number of spiderlings emerge from the nest simultaneously, it can quickly lead to local overpopulation. Competition for available food and cannibalism occur frequently. Baboon spiders disperse by walking away from the mother's burrow. If a favourable patch of ground is found around the burrow of the matriarch, the small spiderling will settle there. They aggregate in such a way that many burrows of juveniles are frequently found grouped around the burrow of the adult female (she is known as the matriarch in the cluster). Such colonies can count up to 106 burrows in 80 square metres. Baboon spider may live up to 25 years and take about 10 years to mature.

Baboon spiders prey on a variety of small animals such as: insects - ants, beetles (e.g. tenebrionids), cicadas, cockroaches, Orthoptera (e.g. grasshoppers, locusts, crickets), Isoptera (termites), Lepidoptera (mostly Saturniidae and Sphingidae, Hymenoptera (driver ants of the family Dorylidae); arachnids - spiders, solifugids and scorpions; millipedes, reptiles, amphibians and snails: frogs and lizards.

Spiders of all stages are attacked by a wide variety of predators, parasitoids and parasites. They are a food source for a number of animals such as: birds, centipedes, reptiles (lizards, chameleons); insectivorous mammals (honey badger, shrews, bats, mice and baboons); other arachnids such as scorpions, solifugids and spiders. They are also attacked by various fungi. A number of insects are specialized predators or parasites of spiders: Hymenoptera (Sphecidae, Pompilidae, Ichneumonidae); dipterous parasitoids (Drosophilidae, Phoridae, Chloropidae); predators of the eggs (Sarcophagidae) and endoparasites (Acroceridae). Spiders also have endoparasites such as the parasitic nematodes of the family Mermithidae.

Large fangs of a baboon spider.Baboon spiders use different mechanisms to defend themselves against their enemies. They use their ability to produce venom to defend them against predators and with their large fangs  they are able to deliver a nasty bite. When alarmed baboon spiders will throw their front legs backwards and open their chelicerae. Some are able to produce a hissing sound similar to snakes, when setae on the chelicerae and palp are Baboon spiders on the defense.rubbed together. The release of urticating hairs from the abdomen of the spider is commonly found in the Theraphosidae of the New World. The hairs can be shed or inserted by direct contact with potential predators by rubbing the region with urticating hairs. Urticating hairs are absent from the theraphosids of the Afrotropical Region.

Some theraphosids are known to deliver painful bites. Harpactira lightfooti, a baboon spider known from Cape Town and the Paarl region in South Africa are fairly aggressive and people sometimes get bitten. They produce a neurotoxic venom. Bites in humans results in a burning pain at the bite site. The patients after about two hours start to vomit; they show marked signs of shock, become pale and have difficulty walking. Bites are however, never fatal.

Owing to the demand for baboon spiders as pets they are classified as Commercially Threatened in terms of the IUCN system. In February 1987 three genera: Ceratogyrus, Harpactira and Pterinochilus were added to Schedule VII of the Transvaal Provincial Nature Conservation Ordinance of 1983 as Protected Invertebrate Animals. This restriction is still in place in all of the South African provinces. Therefore they may not be collected, transported or kept without a permit.

Some of the more common Southern African baboon spiders
Genus CERATOGYRUS (horned baboon spiders). 

The horned baboon spiderThe horned baboon spiders are a very unique genus having a distinct horn-like fovea on the carapace. Unfortunately this makes them very sought after collectors specimens. Ceratogyrus is endemic to Southern Africa and represented by eight species. Their distribution is restricted to the 16 to 28 southern latitude.

The common baboon spider. Genus HARPACTIRA (common baboon spider) 
The common baboon spider is represented by 16 species and is endemic to Southern Africa. Only two species of the 16 are found outside South Africa in Namibia and Zimbabwe. They are large spiders with a body size of between 26-64 mm.

The lesser baboon spiders Genus HARPACTIRELLA (lesser baboon spiders) 
Harpactirella is endemic to Africa and occur in West and Southern Africa and South Morocco. Twelve species are known from Southern Africa. They are slightly smaller spiders and their body size varies from 13-27 mm.

Genus PTERINOCHILUS
After a recent revision the genus Pterinochilus only 10 species are recognized in Africa (Gallon, 2002). They are more commonly found in the Eastern and Central parts of Africa with only two species recorded from Southern Africa.

Starbust spiders Genus AUGACEPHALUS (starbust spiders)
This genus was described earlier this year (Gallon, 2002) and is endemic to Southern Africa. It is represented by two species that occur in the Northern and Eastern parts of South Africa, Namibia, Botswana and Zimbabwe. The generic name refers to the prominent, radial markings on the carapace of the spiders.

Genus IDIOTHELE
Only one species I. nigrofulva is presently recognized from this genus (Gallon, 2002). The species is known from Botswana, Mozambique, Namibia, Zimbabwe and South Africa. Their colour is light brown with yellow striae on a dark background.

Genus TRICHOGNATHA
This new genus is endemic to South Africa and represented by one species (Gallon, 2002). It is known from South Africa as well as Tanzania.


Dr Ansie Dippenaar-Schoeman is a Specialist Scientist at the ARC-Plant Protection Research Institute, Spider Research Centre, Pretoria (rietasd@plant2.agric.za)

Also see: Baboon and trapdoor spiders: an identification manual. Link
             The Spider guide of Southern Africa. Link

References:
Dippenaar-Schoeman, A.S. 2002. Baboon and Trapdoor spiders of Southern Africa: An identification Manual. Plant Protection Research Institute Handbook no. 13, Agricultural Research Council, Pretoria.
GALLON, R.C. 2002. Revision of the African genera Pterinochilus and Eucratoscelus (Araneae, Theraphosidae, Harpactirinae) with description of two new genera. Bulletin of the British Arachnological Society 12: 201-232.

 

 

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