SUMMARY.1. Spatial and temporal variation in the diet of the univoltine predatory stonefly,Kogotus nonus, was studied over 3 years in a small Alberta stream to determine whether the relative abundance of prey types in the diet ofKogotusreflected relative prey densities in the stream and whether the variation in absolute feeding rate was related to either prey or predator density.2. The seasonal shift from sole utilization of Orthocladiinae to inclusion ofBaetisin the diet could not be attributed to seasonal changes in prey density, but was probably related to predator size and ability to handle very active prey. Most of the spatial variation in diet could be related to differences in background prey densities, but very high densities of Baetis caused the predator to specialize on this prey.3. Feeding rate onBaetis. as assessed by per capita gut contents, showed a seasonal shift from a positive correlation withBaetisdensity in winter to a negative relationship with predator density in spring. This suggested that feeding by smallKogotusis a function of prey density. while feeding by later instars is influenced by between predator interactions such as interference.