The diets of the wolf spiders Pardosa pseudoannulata and Pirata subpiraticus were elucidated by direct observation in paddies from July to September 2000. In July, dipterous insects were the most numerous prey consumed by P. pseudoannulata and the second numerous prey consumed by P. subpiraticus, comprising over 50% and over 20% of their respective diets. In contrast, in August, the proportion of dipterous insects decreased dramatically and hoppers were the most numerous prey, comprising over 60% and over 70% of all insects and spiders consumed by P. pseudoannulata and P. subpiraticus, respectively. In September, predators such as wolf spiders and aquatic Heteroptera were frequently observed in their diets. Overall, the green rice leafhopper, Nephotettix cincticeps, was the most numerous prey consumed by P. pseudoannulata and P. subpiraticus, followed by chironomids.

To examine the effects of tillage practices on spider assemblages in rice paddy fields, we investigated the abundance and biomass of spiders in untilled and tilled paddy fields over three cropping seasons (from 1999 to 2001). In total, we collected 6,829 spiders, consisting of 13 species in seven families. The family Lycosidae was the most abundant, followed by Tetragnathidae, Linyphiidae, and Salticidae. Spider abundance and biomass were greater in untilled than in tilled paddies during each cropping season. Although we detected no significant effect of tillage on spider abundance, we did observe a significant effect of tillage on spider biomass in 2000 and 2001. No differences were found in the abundance and biomass of tetragnathid and linyphiid spiders during the cropping season. In contrast, the abundance and biomass of lycosid or salticid spiders tended to be larger in untilled paddies than in tilled paddies, especially later in the cropping season.

To examine the effects of spider predation on pest populations in untilled paddy fields, we constructed life tables for immature stages of the migrant skipper Parnara guttata guttata Bremer et Grey artificially inoculated into untilled and tilled paddies in 2000 and 2001, and conducted a spider removal experiment in 2001. The life tables showed that the migrant skipper larval mortality rate was significantly higher in untilled than in tilled paddies. Unknown factors mainly contributed to this high mortality rate in untilled paddies. The spider removal experiment suggested that the presence of spiders was related to the high mortality rate of migrant skippers in untilled paddies.