An orchard survey determined that nymphs of M. caryaefoliae regularly feed on both surfaces of pecan foliage, while other pecan aphids feed predominately on the lower leaf surface. Aphid populations on laboratory pecan seedlings were similarly distributed. Comparison of M. caryaefoliae nymphs reared on each leaf surface found the upper surface offers no fitness advantage. Observations of aphid density found evidence that crowding by heterospecific aphids contributes to M. caryaefoliae movement to the upper surface, while conspecific crowding has no effect. Field observations and experiments on laboratory seedlings found that some aphidophagous lady beetle and lacewing larvae predominately search the lower leaf surface for prey. M. caryaefoliae may settle on the upper leaf surface because it is a habitat with reduced probability of enemy encounters.