Seasonal and spatial distribution patterns ofCulicoides furens(Poey) andC. mississippiensisHoffman larvae were determined during a 19-mo study of a 5-ha salt marsh located near Yankeetown, Fla. Larvae of both species were found throughout the year in substrate samples taken from all vegetation types (includingSpartinaandDistichlis), but their relative distributions apparently changed according to annual tidal dynamics. Maximum larval production occurred when approximately equal flood index values were recorded; i.e., 0.22 (December–April) forSpartinaand 0.20 (May–September) forDistichlis. These values represent periods of least and most frequent flooding forSpartinaandDistichlis, respectively.C. mississippiensisandC. furenswere most abundant, respectively, inSpartinaandDistichlisareas.