Biocontrol, the use of natural enemies to manage pests, has a long history in agriculture.  It has gained renewed interest because of its importance in sustainable agriculture.  To solve a long-standing puzzle in biocontrol—how well the ubiquitous generalist arthropod predators (GAPs) function as biocontrol agents—this study aimed to 1) quantify the diet composition of GAPs (spiders and ladybeetles) at different crop stages using stable isotope analysis, 2) examine the consistency of GAPs in pest consumption over years, and 3) investigate how abiotic and biotic factors (farm type, crop stage, surrounding vegetation, and relative prey abundance) affect pest consumption by GAPs. Specifically, we sampled arthropod prey and GAPs in seven pairs of sub-tropical organic and conventional rice farms over crop stages (seedling, tillering, flowering, and ripening) in three consecutive years.  Among our sweep-net samples, 352 arthropod predator and 828 prey isotope samples were analyzed to infer predator-prey interactions. Our results show the following:  a) The proportion of rice pests in GAPs’ diets in both organic and conventional rice farms increased over the crop season, from 21-47% at the tillering stage to 80-97% at the ripening stage, across the three study years.  The high percentage of pest consumption at late crop stages (flowering and ripening) suggests that GAPs can function as specialists in pest management during the critical period of crop production.  Regarding individual predator groups, spiders and lady beetles exhibited distinct dietary patterns over crop stages.  b) The high pest consumption by GAPs at late crop stages was similar across years despite variable climatic conditions and prey availability, suggesting a consistency in GAP feeding habits and biocontrol value.  c) The proportion of rice pests in GAPs’ diets varied with farm type and crop stage (e.g., higher in conventional farms and during flowering/ripening stages). Synthesis and applications: By quantifying the diet composition of GAPs over crop stages, farm types, and years, this study reveals that generalist predators have the potential to produce a stable, predictable top-down effect on pests in rice agroecosystems.  Therefore, promoting the field densities of ubiquitous generalist predators will likely enhance pest management and support sustainable agriculture.