We examined diel feeding periodicity of Ephemera simulans nymphs during summer and winter in a third-order stream in central New York. A total of 245 nymphs were collected at 4-h intervals over two 24 h periods and were immediately preserved in 80% ethanol. In the laboratory, we weighed each nymph and its digestive tract. The ratio of wet weight of the digestive tract to the total body weight at each 4-h interval was used to determine feeding periodicity. Diel feeding periodicity followed a similar pattern in summer and winter and was significantly higher at 08:00 hours. Feeding periodicity of E. simulans in Labrador Creek is asynchronous with the two most abundant fish species in the stream and may reflect predator avoidance behavior that has been shown for other mayfly species.