Start the yellow 70D at the 70% mark and wrap back to the bend, then dub a small tight ball of berry microflash dubbing right at the rear. The bright egg sac on the back end is what the fly is named for and it is the trigger a trout sees first from below.
Tie in a strip of 2mm yellow foam at the bend, on top of the shank, pointing rearward, and leave it hanging for now.
Dub a slim yellow body forward from the egg sac to the 65% mark, keeping it thin so the finished fly still looks like a small stonefly rather than a hopper.
Pull the yellow foam forward over the top of the body and tie it down at the 65% mark, then take a couple of extra wraps back through it to segment it. The foam back is the flotation and it also gives the flat-backed silhouette a yellow sally has when sitting on the water.
Tie in a yellow CDC feather at the 65% mark and let the tips lie back over the body as a low wing, no longer than the end of the egg sac.
Spin a second yellow CDC feather in a short dubbing loop and take two turns as a head and legs behind the eye, whip finish, and put a spot of Bone Dry on the foam tie-down only, keeping resin well away from the CDC.