Distribution of linyphiid spiders in relation to capture of prey in cereal fields.

Abstract

Many authors consider spiders to be the most important insectivores in terrestrial communities (e.g. BRISTOWE 1971, ENDERS 1975). Some descriptions of the spider fauna of cereal fields in Europe outside the UK are available (.RAATIKAINEN & HUHTA 1968, ASHIKBAYEV 1973, BASEDOW 1973, HUHTA & RAATIKAINEN 1974, LUCZAK 1975, COTTENIE & DECLERQ 1977, NYFFELER & BENZ 1979a, ROESGAARD & LINDHARDT 1979) but data are sparse for the UK (VICKERMAN & SUNDERLAND 1975, 1977, DUFFEY 1978, LOCKET 1978, FRASER 1982, WALOFF & HASSELL 1982, THORNHILL 1983) and information on spider predation in cereals is very limited (VICKERMAN & SUNDERLAND 1975, FRASER 1982, NYFFELER & BENZ 1982, SUNDERLAND et al. 1984). Linyphiids are the dominant group of spiders in Britain and in all temperate regions of the northern hemisphere (BRISTOWE 1971). Frequently they form more than 90% of the spider fauna in cereal fields, in terms of numbers of both species and individuals (ROESGAARD & LINDHARDT 1979) and the situation is similar in other arable crops (EDWARDS et al. 1975, LUCZAK 1979). They make horizontal, non-sticky sheet webs (described by BRISTOWE 1971 & FORD 1977) and can reach high population densities (e.g. 160 per m² in cereal fields, SUNDERLAND unpubl.). There are some reports that they will also leave their webs and hunt for prey (FOSTER 1972, CHANT 1956, WHEELER 1973) but it is not known how common this is (THORNHILL 1983). This paper reports seasonal variations in the number and composition of the spiders, the position, size and density of their webs, and capture of prey in cereal fields. Data are also given on the variation in prey availability and rate at which prey encounter webs.