The major biological features of 53 of the 70 Swedish species of Sciomyzidae (Diptera: Acalyptratae) are summarized. The larvae are found in many kinds of aquatic and terrestrial habitats, and those of most species are air-breathing, overt, polyphagous predators of aquatic and hygrophilous, non-operculate snails. Larvae of a few species are predators or oligophagous, solitary and internal parasitoids of terrestrial snails, Tetanocera elata attacks slugs, and Antichaeta spp. feed in egg-masses of Lymnaeidae and Succineidae. Knutsonia lineata and certain Renocera spp. are the only insects known to feed obligatorily in bivalve Sphaeriidae.