I almost always find the shucks of numerous stoneflies on the boulders along Father’s Day Creek, my secret trout stream and “spirit-home” in Pennsylvania. I am impressed by three things — the size of the shucks, the abundance of them, and the fact that the transition from such a large nymph to fly takes place when I’m not there. In fact, I have never been there to see it because I don’t fish Father’s Day Creek at night, when most stonefly emergence takes place. (Here’s a great new video that shows the emergence.) All I see is evidence of it, these skeleton-like remains barnacled on the sides and tops of rocks, where the sun bakes them white. It’s one of the mysterious events that occur in the stream. Some stoneflies — and there are hundreds of species in North America — take two years or more to mature. So a large part of their life cycle occurs underwater. By the time they emerge and leave their exoskeletons behind, they have survived a long stretch of time among predators. The stonefly is an important food source for trout — they can represent as much as 10 percent of the invertebrate life in a stream — so if you see lots of their shucks on rocks, you’re usually in healthy waters.
Dan Rodricks 