Although there are many species of Mycetophilidae (or Fungivoridae) and some that are quite common, little is known about the natural history of most species.The literature on the genus Leptomorphus is typically scanty: there are no descriptions of any activities of adults, and only brief descriptions of the general habitat and activities of eggs, larvae, and pupae of one species, L. walkeri (Edwards 1925, Brocher 1931, Madwar 1937).This report, which includes observations on all life stages of Leptomorphus bifasciatus and L. subcaeruleus , is the first study of the natural history of these species.Most of the observations were made during the summer of 1968 near Rensselaerville, N.Y., at the E. N. Huyck Preserve, and a few additional notes were made on individuals found near West Chesterfield, New Hampshire.Leptomorphus subcaeruleus was found near West Chesterfield, and both this species and L. bifasciatus (with L. subcaeruleus most common) occurred on the Huyck Preserve.I discerned no difference in the habits of the two species, and adult males and females of both species were found at the same time at several sites in the Huyck Preserve.Specimens of larvae, pupae, and adults of both species have been deposited in the Museum of Comparative Zoology in Cambridge, Massachusetts.*1 am grateful to the directors and staff of the E. N. Huyck Preserve for generously supporting a summer of