http://www.midcurrent.com/articles/flies/hafele_mayflies.aspx (Oregon’s own Rick Hafele writes a good basic explanation of Mayflies. His fairly recent book (with Dave Hughes) Western Mayfly Hatches, From The Rockies To The Pacific (2004, Frank Amato Publications Inc.) is a great book re Mayflies. Hafele & Hughes rate the importance of various Mayfly characteristics and the Mayflies themselves. There is much to learn and it is not overly technical…a typical feature of Hafele/Hughes work.