There is no more essential fly required to sustain success throughout the season than a small blue winged olive imitation. These abundant mayflies hatch nearly year round, if one includes freestone and tailwater fisheries on one’s itinerary. Over the last ten years I settled on a CDC-wing BWO imitation, and it served me well. The CDC BWO is a tiny comparadun, however, I substitute medium dun CDC fibers for deer hair to form a wing. I tie exclusively size 22 and 24 flies, and deer hair contains too much bulk for these diminutive replicas of the baetis mayflies that populate Colorado streams. A slender profile is necessary to convince selective blue winged olive feeders to mistake my flies for naturals.
A critical feature of the CDC BWO is the delicate split tails. I use dun microfibbets and strive to create two tail fibers that split at forty-five degree angles from each side of the hook shank. Historically I struggled to acheive this goal while maintaining the tail fibers on an even plain. Last year I searched online and found a brief instructional piece that solved my problem. When I attach the thread, I make a small bump at the rear of the hook shank, and then allow a three inch tag end of the thread to dangle. I tie two microfibbets to the top of the shank and make thread wraps back until I am 1/8 inch from the thread bump. Next I pull the tag end of the thread upward and split the tails and then pull forward and down until the near fiber approximates the position I desire. I switch hands and hold the tag thread with my right hand while I lock it down with a couple thread wraps with the bobbin in my left hand. I once again switch hands, and I continue wrapping thread back toward the bump with my right hand as I preen the fiber on the far side into the correct angle and position. I find that this technique yields nearly perfect split tails every time.
I counted nineteen size 24 olives in my combined fly bins, so I manufactured six additional imitations to bring my total to 25. Next I inventoried my size 22 supply and discovered 34, so I made an additional six to bring my total to 40. If I am lucky, these flies will see action in the not too distant future, as blue winged olive hatches often commence in the middle of March.