The North American sawflies (Hymenoptera) occurring north of Mexico with larvae feeding on ferns (Polypodiopsida) are reviewed. They include the introduced European stipe borer Heptamelus dahlbomi (Thomson) (Heptamelidae) and 21 external feeders in the tribes Aneugmenini and Strongylogastrini (Tenthredinidae: Selandriinae). Host and distribution records are summarized for each species, and descriptions of larvae are provided where available. The first USA records are given for the introduced Palearctic species Strongylogaster macula (Klug) (previously known from Canada). New host records include: Athyrium asplenioides var. angustum (Willd.) T. Moore (Athyriaceae) for Aneugmenus flavipes (Norton), S. macula, and Thrinax albidopicta (Norton); Onoclea sensibilis L. (Onocleaceae) for S. impressata Provancher; and Osmunda claytoniana L. (Osmundaceae) for S. polita Cresson. A list of fern species and their sawfly associates is provided, including descriptions of unidentified larvae.