Eleven species of the genus Ledermuelleria Oudemans were collected from mosses obtained at many localities in southern Quebec and in eastern Ontario (Canada), and also in the northeastern U.S.A. Altogether 160 moss samples were collected, almost half of which harboured the mites. The mosses comprised 55 species, 38 being Ledermuelleria-associated. Habitat records suggest that L. arctica Wood, L. gersoni ·wood and L. rhodomela (KocH) mostly occur on mosses colonizing open soils, whereas L. frigida Habeeb prefers moss growing in shaded, very humid places. L. frigida was studied in the laboratory. It feeds on moss leaves, sucking out cell contents but leaving cell-walls intact. The life cycle lasts about 30 days (at 23 ± 20 C). Reproduction is arrhenotokous, as isolated females have only male descendants. Females, whether confined with males or isolated, laid about 21 eggs. The mites reproduced freely under both long-day (r6 hours) and short-day (g hours) photoperiodic regimes. Transfer experiments showed that L. frigida will feed and survive on many moss species. Reproduction, however, occurs only whilst feeding on a few of these. Eggs placed in distilled water hatched and the larvae developed to the adult while thus immersed, but no oviposition took place under water. The species L. rhodomela, L. clavata (Canestrini and Fanzago) and L. schustteri Summers and Priee also fed on various mosses and had similar life cycles.