Hendricksons are the East's first major mayfly hatch of the year. They emerge in mid-to-late April through early May, bringing rising trout to the surface for the first time after winter. Sizes 12–14 — bigger than most spring mayflies, which makes them satisfying targets.
The classic pattern is a Hendrickson Comparadun or a Catskill-style dry. The hatch is often heavy enough that fish key on duns specifically; a good drift in the seam below a riffle will produce.