The life history of Gynaephora groenlandica was studied in the high arctic at Alexandra Fiord, Ellesmere Island. Life history events occurred only in the 3-4 weeks before mid-July. Larvae fed mainly on Salix arctica . They stopped feeding by the end of June, hid, and spun hibernacula. Nineteen percent of third- and fourth-instar larvae were parasitized by the wasp Hyposoter pectinatus (Ichenumonidae); 52% of fifth- and sixth-instar larvae and pupae were parasitized by the fly Exorista sp. (Tachinidae). The authors estimated that G. groenlandica has a life cycle lasting 14 years. Parasitism caused 56% of overall mortality, whereas cumulative winter mortality was calculated as 13% of a cohort passing through a 14-year life cycle. The importance of parasitoids in the life history of G. groenlandica suggests that parasitism is as significant as climate in population regulation of insects living in the high arctic. none