May Long Weekend Flashbacks

One hatch that you will likely encounter on most trout streams this May long weekend will be Blue Winged Olive mayflies (Baetis). This hatch really is a one stop smorgasbord that provides opportunities for trout to feed on all stages of the mayfly lifecycle. Baetis Nymphs are the prime target during pre-hatch migration and in the early stages of a hatch, and Emergers provide consistent surface action once the hatch gets rolling. But if these two life stages are considered to be the main meal, then it is the adult spinners that are served up as leftovers the day after.

Most fly anglers are familiar with a conventional spinner fall – once adult spinners have completed the task of laying eggs they fall to the surface with wings spread and float helplessly downstream.  Trout capitalize on this easy meal whenever possible, and the appropriate spinner pattern can be quite effective in the morning hours after a mayfly hatch. But some Blue Winged Olive mayflies (along with several species of caddisflies and damselflies) have a different egg laying strategy that exposes them to trout in an entirely different manner. I am talking about mayflies that crawl under water to lay eggs on the undersides of rocks and logs rather that fluttering over the water and dropping their cargo on the surface.

BWO adult spinner as it disappears below the surface
(once fully submerged the wings will slick back from their traditional upright position)

As the female spinners crawl under water their wings press back over the body and trap air that will sustain them through the egg laying process. The trapped air gives the adults a silvery sheen that is visible from quite a distance. Once egg laying is complete the spent adults are swept downstream, tumbling in the current. The slicked back wings still have air trapped on, or under them, and this is what many trout key in on when feeding on the submerged spinners.

The ubiquitous flashback pheasant tail nymph is a pattern that effectively imitates drowned BWO spinners. The wing case is tied with some sort of reflective material – usually silver tinsel, but Crystal Flash is also a popular choice. One school of thought is that the reflective wing-case represents air trapped under the cuticle of an ascending nymph. But that sheen can also look like the air trapped under the wings of a spent egg laying adult.

While the flashback pheasant tail nymph can be an effective choice when fished the morning after a Baetis hatch, a better choice is to tie a slim, mottled olive nymph-like pattern with the reflective material tied in as a trailing set of wings that reach beyond the tip of the abdomen. My preference is for two strips of silver Flashabou (at least on the smaller sized flies) tied in as a trailing wing.

This weekend is looking like a prime Baetis weekend; with the forecast calling for cooler temperatures and a little rain, hatch conditions will be optimal. Be prepared with #16-18 BWO nymphs for early hatch activity, emergers for the peak of the hatch, and some flashback “nymphs” to cover the spinner drift the following morning.