This is a very important stage, because the mayfly is very vulnerable. Many mayflies are eaten when they are an emerger because they are still subsurface, making this an important stage to understand. Trout feeding on an emerger can usually be seen visually as a dry fly feeding fish. This can easily be distinguished by watching the way the fish is feeding. If the trout is rising dorsal fin, tail, then kicking down either creating a bulge or splashy rise it is usually feeding on an emerger.
Large trout feeding on emergers usually just create a bulge.
The key is to see if the fish is showing its head, and if it is not then it is usually feeding on an emerger just subsurface. Seeing a hatch of mayflies, or being in the middle of one is a wonderful experience. These bugs hatch either under the water and swim to the surface, hatch on top of the water, or crawl to shore or a nearby rock to shed its shuck. At this time mayflies can be seen in the air, riding the water's surface, or fleeing to a nearby tree to await for its reproductive organs to develop. When the mayfly is fully developed it will mate preparing the female for egg laying.