none Eggs of Korscheltellus gracilis (Grote) hatch after 16-19 d at 22 degree C in saturated atmospheres. Most larvae take 2 yr to mature, then pupate in elongate cocoons spun in forest floor litter in late May and June of the second year. Adults emerge about 1 mo later. Larvae are among the most polyphagous Lepidoptera, consuming leaf litter, fungi, mosses, and below-ground tissues of sundry ferns, gymnosperms, and angiosperms. Egg, larval, and pupal stages of K. gracilis are described and illustrated. Characters serving to differentiate larvae and pupae of K. gracilis from other sympatric Hepialidae are discussed. Two tachinids, Lixophaga unicolor (Smith) and a species of Lydina Robineau-Desvoidy, and the ichneumonid, Pterocormus feralis (Cresson), are parasitoids of the immature stages. Mesodiplogaster sp., a diplogasterid nematode, commonly infests the larvae. Three entomophagous fungi, Beauveria Vuill., Entomophthora Fres., and Hirsutella Pat., are pathogens.