Coremacera marginata (Fabricius) (Dipt. Sciomyzidae) is found in woods, fields, and other terrestrial situations in much of the western Palearctic region. During laboratory rearings through the complete life cycle, each larva killed and ate I-3 immature to adult snails belonging to several terrestrial genera. The immature stages of C. marginata are described and figured, and the distribution is mapped. The taxonomic position of Coremacera is discussed, and a catalog of the genus and new distributional records of 4 rare species of Coremacera are included. A summary chart of the food of sciomyzid larvae is presented.