As part of an investigation to estimate the effect of resident spider populations onErythroneura variabilisBeamer, spider species composition, relative abundance, and seasonal occurrence were determined. Spiders were sampled monthly during the 1992 and 1993 growing seasons; their numbers were pooled and analyzed for species diversity using the Renkonen index of similarity and cluster analysis. Twenty-seven species of spiders were recorded, representing 14 families. The most common species wereCheiracanthium inclusum(Hentz),Trachelas pacificus(Chamberlin and Ivie),Theridion dilutumLevi,Theridion melanurumHahn,Oxyopes scalarisHentz,Oxyopes salticusHentz,Hololena nedraChamberlin and Ivie, andMetaphidippus vitis(Cockerell). Three species (C. inclusum,T. dilutum, andT. melanurum) constituted>30% of all spiders collected; however, species diversity varied among vineyard sites. In 4 vineyard sites, hunting spiders (C. inclusum,T. pacificus,Oxyopesspp., andM. vitis) dominated the fauna, representing an average of 79.7% of the specimens collected. In the other 3 vineyards, hunting and web-weaving spiders were more equally represented, averaging 43.5 and 50.0%, respectively, of all spiders collected. Species similarity between vineyards from both years ranged from 19 to 73% based on the Renkonen index. Similarly, cluster analysis showed a wide separation in species composition among sampled vineyards. The discrepancy in species similarity among sampled vineyards is discussed in reference to potential prey density and vineyard cultural practices. Seasonal abundance patterns of the 8 most common species are presented and discussed in reference to their respective phenologies.