Predation on the eggs and adults of native Hawaiian lymnaeid snails by two non-native species of sciomyzid flies, marsh fly "Sepedomerus macropus" and "Sepedon aenescens" represents a significant threat to the survival of Newcomb's snail. They feed on lymnaeid snails and were introduced into Hawaii in 1958 and 1966, respectively. These predatory flies were intended to act as biological control agents for the non-native lymnaeid snail "Galba viridis" (="Fossaria viridis"), (an intermediate host of the cattle liver fluke "Fasciola gigantica"). These biological control species may represent a significant threat to Newcomb's snail and other native lymnaeid snails.