While fishing a quiet stretch of the Gunpowder River on Friday, I noticed a good stonefly hatch along the banks of a small glide. The size #16-20 stonefly adults crawling along the rocks, logjams and snow banks could easily have gone unnoticed as there were only two to three winged adults per foot spread over both banks. Few of the adults were flying about, as most were engaged in the act of mating or crawling on the snow. The sun was at just the right angle and intensity for a series of days to cause the stoneflies to emerge. Most of the stoneflies were a size #18-20 with a black body and mottled gray wing. A few larger size #14-16 dark brown stoneflies with a tan mottled wing were also present. This video short shows an up close look at these often elusive winter insects on a 42 degree day with bright sun.
Even with an abundance of insects, anglers walking and looking for rising trout may not notice a stonefly hatch. The adults tend to crawl more than fly and can remain unseen amidst the debris on the water’s edge. A single stonefly in flight, may not appear as much of a hatch, but may indicate that many more are present on the banks. Under ideal conditions, adults gather along the river’s edge and take to the wing in spurts, cued by mating and optimal conditions, bringing numerous trout to the surface.
The trout feed in sporadic bursts as the adults land in the water and may not rise until the next group of adults repeat the cycle. The cycle of rising trout to naturals can occur a few times an hour or more if the hatch really gets going. The sun and air temperature help determine this, but I have had good days when the air was in the upper 50s with intermittent sun, or in the low 40s and bright sun. Sections of river in direct sunlight over a series of days will have more insect activity, than areas shielded from the sun by hillsides.
On days when the trout are rising to stoneflies or midges the dry fly action is exceptional. Nymph fishing is effective all winter on the Gunpowder, but extremely effective when stonefly adults are present, and few fish are rising. Small black pheasant tails, wire nymphs, and sunk adult stonefly patterns are best fished close to banks, rocks and log jams. A size #18 black PT nymph produced five browns in quick succession at one pool where the bugs were hatching. The surface action never really got going that day, but the action on nymphs was steady in deeper areas.