Larvae of six species of Sciomyzidae, commonly called marsh or snail-killing flies—New Zealand's Eulimnia philpotti Tonnoir and Malloch; the Palearctic Ilione lineata (Fallén); the Nearctic Renocera cressoni Mathis and Knutson, R. longipes (Loew), and R. pallida (Fallén); and the Holarctic R. striata (Meigen)—kill and feed only on freshwater Sphaeriidae clams. These sciomyzid species are the only insects that are well documented as obligate natural enemies of bivalve Mollusca. Herein we report on the sciomyzid genus Renocera Hendel, 1900, one of the most biologically and phylogenetically important genera of this extensively studied family. We present a comprehensive taxonomic revision of the six valid species of Renocera: R. cressoni, R. johnsoni Cresson, R. longipes, R. pallida, R. striata, and R. stroblii Hendel. We divide the genus, for the first time, into subgenera: Aporenocera, new subgenus, comprising only R. johnsoni, and Renocera sensu stricto, comprising the other five species. We compare the distribution and biology of immature stages of E. philpotti and I. lineata with those of Renocera species, discuss our results and conclusions in relation to cladistic analyses of Sciomyzidae and to the evolution of behavior in Sciomyzidae, designate lectotypes for Sciomyza affinis Zetterstedt, R. pallida, and R. stroblii, describe the subgenera Aporenocera and Renocera sensu stricto, rede-scribe the six valid species of Renocera, and place Renocera lyami Withers, new synonym, as a junior synonym of Tetanocera arrogans Meigen.