Spiders are one of the commonest predator groups found in agro-ecosystems in South Africa. They have special adaptations towards a predatory way of life. Their soft abdomens enable them to consume large amounts of food in relatively short periods of time, while their rate of predation may greatly increase during short periods when plentiful supply of food is available. They have an exceedingly high resistance to starvation, which enables them to survive and maintain normal reproduction during periods of low prey availability. This is accomplished by the ability to decrease their metabolic rate. During their lifecycle, which varies from 9 months to 25 years, all instars feed actively as predators. Most spiders are polyphagous and feed on a variety of prey but some are specialists. Predation is not limited to adults only but includes the egg and larval or nymphal stages.

Insect predators and predacious mites have received much attention in biological control programmes of mite pests, while spiders appear to have been neglected. The natural occurrence of adult and immature spider species on plants places them in close contact with plant feeding mites. Laboratory experiments done at ARC-PPRI suggest that a variety of mites found on cultivated crops, are consumed by spiders while field experiments showed that spider populations have the potential to reduce a population of mites in certain crops to such a level that an substantial increase in yield may be expected.

Spiders can also inhibit the initial build-up of prey populations. The use of spiders as biological control agents will demand the conservation and possibly the augmentation of spiders in cultivated fields. This presents difficulties, as rearing techniques are as yet prohibitively time-consuming and expensive. Husbandry of spiders should rather be accomplished by means of environmental manipulation through adapted farming practices.

Further reading:

Dippenaar-Schoeman, A.S. 1976. An ecological study of the spider population in strawberries with special reference to the role of Pardosa crassipalpis Purcell (Araneae: Lycosidae) in the control of Tetranychus cinnabarinus (Boisduval). MSc thesis-Rand Afrikaans University 119 pp.

Dippenaar-Schoeman, A.S. 1977. The biology of Pardosa crassipalpis Purcell (Araneae: Lycosidae). J. ent. Soc. sth. Afr. 40: 225-236.

Dippenaar-Schoeman, A.S. 1979. Spider communities in strawberry beds: seasonal changes in numbers and species composition. Phytophylactica 11: 1-4.

Dippenaar-Schoeman, A.S. 1979. A simple technique for study feeding behaviour of spiders on mites. Bull. Br. arachnol Soc. 4(8): 349.

Van den Berg, A.M. & Dippenaar-Schoeman, A.S. 1991. Spiders, predacious insects and mites on South African cotton. Phytophylactica 23: 85-86.

Lycosidae: Pardosa crassipalpis

Spiders in Agro-Ecosystems

Spiders in cotton orchards

Spiders in macadamia orchards

Spiders in citrus orchards

Spiders in pistachio orchards

Spiders in avocado orchards

Spiders in strawberry fields

Spiders on grapes

Spiders as predators of termites