Tiny Baetis mayflies are perhaps the most commonly encountered and imitated by anglers on all American trout streams due to their great abundance, widespread distribution, and trout-friendly emergence habits.
Roguerat's advice about using only a wisp of a wisp is good stuff.
There's not one ounce of fat on that bug...He's just built like a fire-plug. :) He is the Jake LaMotta of mayflies...