The Slate Drake is an important mayfly hatch, particularly in the Eastern US, with an emergence that can run from May through September.
Slate Drake Emerger Material List
Hook: Dai-Riki #125, Size 12
Thread: Danville 6/0, Olive
Trailing Shuck: Z-lon, Brown
Body: Dry Fly Dubbing, Isonychia
Wing: Comparadun Hair, Dun