Tie in a forked moose hair tail, split the fibers into two bunches with figure-8 wraps. Drakes are big mayflies; the tail should be a good shank length.
Tie in the yellow floss rib at the bend.
Dub a robust olive body forward to the 65% mark, fuller than your usual mayfly, with a real taper.
Spiral the yellow rib forward in 4-5 evenly spaced turns. That yellow-over-olive segmentation is a signature of the natural.
Stack and tie in an upright elk hair wing, one shank length tall.
Wrap two olive-dyed grizzly hackles behind and in front of the wing, packed reasonably dense. This fly needs to float a big body.
Whip finish, cement.
Substitutions
Body instead of Olive dubbing: Olive Superfine — Clean dubbing for the big body; Olive/yellow blended dubbing — Yellowish olive match
Tail instead of Moose body hair: Brown bucktail — Similar stiffness; Micro Fibbets — Precise split, durable
Wing instead of Elk or deer hair: Coastal deer hair — More buoyant for this big fly; Dyed olive deer hair — Matches the overall green tone
Other versions
3 more in the app: Gregg Dressing (1940), Fly Fish Food Tie, Jigged.