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.

Stoneflies - Round Two

I was out poking around on a few central Alberta trout streams this past weekend. Conditions were reasonable on Saturday – a little murky on most streams but definitely fishable. Winter stonefly hatches are winding down on the lower elevation streams with just a few Zapada cinctipes hanging around.

Zapada cinctipes (adult female)

Caddisflies are coming off sporadically. I noted two species of Limnephilus; one was your typical cinnamon sedge in size 12, the other was a smaller gray species in size 14 (sorry no specimens or photos).

The most significant hatch that is just coming on line is the Skwala stonefly hatch (Skwala americana or Skwala curvata, or both depending on your location). This hatch is the first of the larger stoneflies to hatch in the spring and when it is just starting, it is often missed by the casual observer. Early in the hatch, and before the streamside shrubbery has developed any leaves, there are few places to hide. For this reason, Skwala stoneflies spend most of their time hiding under the streamside rocks. Many anglers assume that the hatch is just trickling off when in fact it is moving along quite nicely – it’s just that most of the action at this point is out of sight.

If you lift a few rocks along the margin (in the water or just out of the water) you will see both nymphs staging in the shallows waiting to emerge, and adults that have just emerged and are waiting for their wings to fully extend and harden.

Skwala americana (nymph on stream margin ready to emerge)

Skwala americana (newly emerged adult female
waiting for wings to extend)

The males are easy to pick out as they are generally the most active of the sexes early in the hatch (waiting to ambush females as they emerge). Males have reduced wings (about half the length of “normal” wings) while the females have fully developed wings. Both sexes can have bodies up to 20 mm long and the wings of the female can extend to 25 mm. The undersides of the adults are generally shades of mottled yellow/olive and black.

Skwala americana (male and female in copula)

 

Skwala americana (adult male with reduced wings)

 

But at this stage of the game fishing a nymph is the way to go (dry fly action will not pick up until there are enough females returning to the water to lay eggs). Most of the action will take place late in the afternoon and into the evening. Look for current seams in areas with moderate to fast current and lots of fist size or larger rocks.