It is important to know the specific mayflies that will be hatching as the season progresses so you know which fly with which to fish. An easy way to predict this as I see in 30 years of my stream notes is to watch the wildflowers in the mountains.
*When the blood root is out full the Quill Gordons are hatching well so use a Mr. Rapidan Dry size 14.
*When the Trillium are beginning to break through the little Blue Quills are on in good numbers so use a Blue Quill Dry size 16 or 18.
*When the Trillium are out full all around the streams the March Browns are hatching well so use a Mr. Rapidan Dry size 14.