They then emerge into the air, where they hang onto trees, rocks, or other stable structures. During this phase they are called subimagos. After molting one more time, the mayflies are sexually mature adults, and mating ensues. The female then rests on the surface of the water it lived in just one to two days before, where she lays eggs that fall to the bottom of the stream to restart the cycle. Trout of all sizes feed on mayfly nymphs, visually spotting them as the mayflies forage for their food - algae and other plants growing on the surfaces of underwater rocks, as well as dead leaves that have fallen to the bottom of the stream.
Trout also feed on adult mayflies while they rest on the water's surface to lay their eggs.
All of this makes mayflies good organisms to test for anti-predator responses that would occur only in the presence of trout. The specific objective of this study was to determine if mayflies from the family Heptageniidae showed behavioral responses to trout odor. As mayflies are heavily preyed upon by trout, it is reasonable to predict they have some anti-predator mechanisms to avoid them. They found that in the presence of trout odor, mayflies more often remained stationary during the day and drifted through the water at night. The behavioral responses that this summer's study looked at were much smaller and more intricate than the water column position used by McIntosh and Peckarsky.