Understanding how community composition of service-providing organisms affects ecosystem functioning is a key challenge in ecology. Although it has been proposed that taxonomic diversity and functional traits mediate this relationship, how several facets of community structure affect the delivery of key ecosystem services remains to be explored. In this study, we investigated how abundance, taxonomic richness as well as the shape of biomass distribution in predator communities affect biological pest control services in vineyard landscapes. Our analyses were based on a dataset combining samples of arthropod predators, measures of predation rates of grape pests and characterization of environmental covariables for 42 fields located in South-Western France. We found that beside the abundance or the taxonomic richness of predators, the shape of biomass distribution (mean, variance, skewness and kurtosis of the distribution) influences the level of biological control. Predator communities largely dominated by low biomass species provided the bulk of biological control services. Lower levels of predation resulted from increased proportions of large biomass species and more evenly distributed biomass values in the communities. Our results indicate that the top-down control provided by low biomass species decreases as the relative proportion of large biomass species increases in the predator community. This suggests that biological control may be affected by negative interactions (e.g. intraguild predation, behavioural interactions) between predators arising from the recruitment of large individuals in the community. Our study revealed that the shape of biomass distribution is a major aspect of functional diversity in predator communities providing insights into the mechanisms that link biodiversity and ecosystem services. While our study focuses on biomass, considering other traits involved in trophic interactions may increase our ability to predict the level of biological control in ecosystems. A freePlain Language Summarycan be found within the Supporting Information of this article.