Ferrissia wautieri, a freshwater limpet, is a widely distributed species in The Netherlands. In a pond near Nijmegen samples were taken twice a month over the year to study the population size and structure of this species in relation to the water temperature. Only ancyloids were found. Production of juveniles is temperature-dependent; peak numbers occurred in July and August. Just-hatched juveniles (shell length 0.6 -1.0 mm) occurred over a lengthy period in the year, but were absent in March and April. During these months the collected numbers of specimens were very low. The largest specimens were collected dudng March, April and May.