Diet composition of Gerris lacustris in a rice-field was compared with the composition of insect fauna from sweep nets conducted in the same habitat. Diptera was the most common prey among the insects potentially available to waterstriders. Water striders consumed Diptera, Homoptera and Hymenoptera in larger proportions than proportions of these orders in the sweep samples. There was no indication of prey size preferences in water striders as they appeared to capture prey of various size classes in frequencies corresponding to the frequencies in sweep samples. This is the first report of the diet of G. lacustris and the second report of the diet composition of any Gerris sp. water strider.