Farming relies heavily on pesticides in order to maintain/increase crop production, yet, awareness of the adverse effects of pesticides on the environment and on biodiversity has triggered the search for alternative, non-chemical, pest management strategies. In arable systems, weeds remain one of the most challenging management issue. Recent research suggest that the depletion of weed seeds by naturally occurring seed consumers could impact the dynamics of problematic weeds and in temperate systems, carabid beetles are the main invertebrate consumers of weed seeds. However, predicting weed seed depletion rates in field conditions remains difficult, as carabid trophic responses are still not clearly understood. In particular, density-dependence could strongly affect the outcome of this trophic interaction and thus the potential of carabid beetles to deliver the weed seed predation service. In this study, we conducted microcosms experiments in order to assess how weed seed density and carabid density affect the weed seed consumption rate of Poecilus cupreus and Harpalus affinis. Two weed species were tested, Taraxacum officinale and Viola arvensis. The microcosms were 45 x 30 cm boxes filled with sand; three experiments were conducted, i.e. two for P. cupreus with the two seed, and one for H. affinis with T. officinale. In each experiment, four modalities were tested (7 replicates) that were combinations of carabid density (1 or 6 individuals) and weed density (100 or 200 seeds for T. officinale and 25 or 100 for V. arvensis). Experiments were conducted for several consecutive days and the daily number of seeds eaten was monitored. We hypothesized that (i) the predation of weed seeds is positively correlated to the density of carabid beetles and to the density of weed seeds and (ii) the per-capita carabid consumption depends on the density of carabid beetles due to interactions between individuals. Our results generally validate these hypotheses but also suggest that these relationships are strongly dependent on the strength of the trophic interaction between each pair of carabid and weed species.