John Bush’s Styrofoam and Pantyhose Emerger Fly (from Skip Morris book) Recipe:

Hook: Tiemco 2487 size 16-20, could use Tiemco 100, light wire is desirable
Thread: Olive, could use any small diameter thread, any appropriate color
1) styrofoam ball approx. 1/8” diameter wrapped in
2)panty hose, approx. 1” square
Abdomen: thread base
Shuck: Sparkle emerger yarn, may have to split strand with bodkin

Debarb Hook, set in vice.
Start thread wrap behind hook eye and wrap shank halfway to across from hook point and back to behind eye.
Use bodkin to tease styrofoam ball out of packing material.
Place that ball in the middle of a one inch square piece of pantyhose and gather it around the ball.
Tie the gathered panty hose material to top of hook securely.
Cut off excess of panty hose material.
Tie on sparkle emerger yarn to make a trailing shuck.
Continue wrapping thread to build a slight taper between panty hose material and hook shank.
Cut off any shuck material ahead of tie-in point, leaving trailing shuck.
Wrap thread forward to just behind the hook eye and whip finish.
Trim trailing shuck material to desired length (approximately the length of the thread abdomen).

Fish it to imitate an emerger at the underside of the water surface.

This fly recipe is a generic emerger pattern that can be modified to imitate a number of insect variations. The shuck could be sparkle emerger yarn, antron, or any substitute of your choice.  John used sparkle emerger yarn for this one because it was supposed to imitate a blue winged olive. You could use antron in a brown olive color for a PMD imitation.