1. Between April 1963 and March 1964 the drift activity of five species of Hydrachnellae was analysed at two-hourly intervals in the "Breitenbach", a brook which flows into the Fulda river. 2. Sperchon glandulosus, Sperchon setiger and Atractides nodipalpis are day-active, Lebertia glabra is night active and Lebertia salebrosa is twilight-active. 3. The annual periodic pattern of the drift activity of Lebertia glabra, Lebertia salebrosa and Atractides nodipalpis has one peak, that of Sperchon glandulosus and Sperchon setiger two peaks. 4. The two Lebertia species have their daily drift maxima at different times, their yearly drift maxima, however, are simultaneous. The two Sperchon species have their daily drift maxima at the same time, their yearly drift maxima, however, differ by two months. 5. A large number of oviferous females are found during the yearly drift maxima. The drift is correlated with spawning and a possible colonization cycle for Hydrachnellae is discussed.