none Larvae of Chirosia betuleti cause the formation of cover galls in the vegetative leaves of the ostrich fern, Matteuccia struthiopteris. This is the first record of this anthomyiid fly in North America. Females lay their eggs on the unfurling fronds. Newly emerged fly larvae feed on glandular hairs causing the pinnules to curl around the midrib, and partially or completely loop around the feeding larvae. Fly eggs and larvae have been found contaminating the fiddleheads of this edible fern. Larvae were parasitized by braconid wasps of the genus Aphaereta and eulophid wasps of the genera Dimmockia and Elachertus. Larvae of the chloropid fly, Elachiptera costata, were secondary invaders of the vacated galls. Larvae of Chirosia betuleti and Elachiptera costata are described in detail for the first time. Effects of the gall on leaf growth are outlined, and the distribution of the galls in a sampled population is described. A cursory description of a gall caused by the tortricid moth, Olethreutes auricapitana, is given, and a list of the primary insects collected and identified from the fern is also provided.