Sciomyzidae of 6 spp. in 5 genera were reared from larvae that fed on living or freshly killed snails. Since flies representing 5 additional genera have been reared from snails by others, larvae in 10 genera distr. among 3 subfamilies of Sciomyzidae apparently feed on snails. Snail eating appears therefore to be widespread among larvae of this family, and the Sciomyzidae may serve as subsequent hosts of helminth or protozoan parasites found in snails. Reared larvae of the tetano-cerine genera Dictya, Hedroneura, Sepedon and Tetanocera attacked snails of at least 9 spp. in 6 genera (mostly aquatic), killed them quickly and consumed most of the soft parts in a few hrs. It is suggested that these relatively unselective snail predators may prove useful in the control of undesirable snails. Additional data on biology, morphology, ecological relationships and seasonal aspects of Nearctic Sciomyzidae are presented. Living or reared specimens of Diptera that feed on snails are solicited.