Spiders are polyphagous and feed on a variety of available prey. Predation is not limited to adult insects only, but include the egg, larval and nymphal stages as well. As predators, spiders have a two-fold function. Not only do they feed directly on their prey, but their presence causes indirect mortality. The presence of spiders could disturb larvae who then drop from the plant and die, while the webs spun over the leaves also seem to make them less suitable for oviposition and feeding. With increased interest in non-chemical control strategies, the need to understand the diverse group of organisms that might play a role in our agro-ecosystems is increasing. It is predicted that hundreds of potentially useful biological control agents are still unknown to man. Thus before they can be economically used, these organisms must be collected, studied and integrated into our information systems. Therefore surveys of the araneofauna are essential before experimental work could be carried out.

Spiders were collected from 1977-2000 in 10 citrus-producing areas in South Africa. Thirty-five families, represented by 134 genera and 197 species were recorded. The Thomisidae were the richest in species (28) followed by the Salticidae (23) and Araneidae (22). The spider species with the widest range was Pardosa crassipalpis Purcell (Lycosidae) which have been collected from six of the localities followed by three orb web species, the sac spiders Cheiracanthium furculatum and a Clubiona sp, Enoplognatha sp. (Theridiidae), Eperigone fradeorum (Berland) (Linyphiidae), and Misumenops rubrodecorata Millot (Thomisidae).

The wandering spiders constituted 61.5% of the spider fauna collected and the web-builders 38.5%. Information on guilds, relative abundance and distribution are provided for each species in an annotated checklist. Spiders are common and occur in high numbers in citrus orchards and prey on a variety of citrus pests. Although spiders may be incapable of controlling major pest outbreaks by themselves their role in a complex predatory community may be important in regulating pest species at low densities early in the season and in between peaks of pest species activity. They therefore could play an important role in keeping pests at endemic levels and preventing outbreaks. This survey forms part of the South African National Survey of Arachnida (SANSA) in agro-ecosystems.

Peter Stephen (Citrus International); Dr M. van den Berg (ARC-Institute for Tropical and Subtropical Crops)

Read more:
Dippenaar-Schoeman, A.S. 1998.
Spiders as predators of citrus pests. In: Bedford E.C.G. & Van den Berg, M.A. (eds). Citrus pests in Southern Africa. Agricultural Research Council, Nelspruit.

Dippenaar-Schoeman, A.S., Van den Berg, A.M. & Stephens, P. (in preparation). Species in South Africa citrus orchards: species diversity and abundance (Arachnida: Araneae)

Stephen, P.R., Grout, T.G. & Dippenaar-Schoeman, A.S. 2001. The abundance and distribution of spiders in the South African citrus ecosystem. Abstract of the 15th International Congress of Arachnology, Badplaas South Africa p. 164.

Van den Berg, M.A., Dippenaar-Schoeman, A.S., Deacon V.E., Anderson, S.H. 1992. Interaction between citrus psylla, Trioza erytreae (Hem. Triozidae), and spiders in an unsprayed citrus orchard in the Transvaal Lowveld. Entomophaga 37(4): 599-608. [Pdf]

Sampling the citrus orchard

Miturgidae: Cheiracanthium sp.

Spiders in Agro-Ecosystems

Spiders in cotton orchards

Spiders in avocado orchards

Spiders in macadamia orchards

Spiders in pistachio orchards

Spiders in strawberry fields

Spiders on grapes

Spiders as predators of termites

Spiders as predators of mites

Clubionidae: Clubiona sp.