Rates of encounter with sedentary and active prey vary with a preda- tor's activity level. Experiments were conducted to determine whether observed changes in the diet of Nephelopsis obscura Verrill (Hirudinoidea:Erpobdellidae) could be attributed to reduced activity levels when hunger level is reduced. Activity levels of leeches were recorded for 1 hr in the light and the dark; when starved and when fed. The leeches were more active before feeding than after feeding, and more active in the dark than the light. These observations appear sufficient to explain the observed diet changes.