I have been using this pattern with tremendous success over the past few years when Needle Fly (small stoneflies) are fluttering about. Particularly good in fast water and I had one of my clients hook and land 30 fish one day with this pattern.
I originally thought that these flies had a small egg sac attached when they were ready to lay eggs. I presumption I have since discounted this idea but have kept it in the pattern.
This fly also works well as a Grannom.
Hook: Teimco 103BL
Thread: Black Uni 8/0
Tag: Flouro tying silk
Body: CDC
Wings: 2 CDC tied 'wonderwing style'
Thorax: CDC