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.