I can’t recall the last time someone spoke with me about stoneflies—you know, the order Plecoptera? There are reasons for that, especially here in the Eastern U.S. and, in particular, our …
I can’t recall the last time someone spoke with me about stoneflies—you know, the order Plecoptera? There are reasons for that, especially here in the Eastern U.S. and, in particular, our rivers in the Catskill Mountains. For one thing, most of the stonefly species indigenous to this region—and there are several—emerge at night, particularly the larger ones. Secondly, stoneflies are not as widely distributed in Catskill rivers as mayflies and caddisflies. The irony here is this: Where larger flies are present, they make up a significant portion of the biomass that constitutes trout food; we’re talking nymphs that measure up to two inches in length and that take up to three years to mature and hatch, compered to our largest mayfly, the green drake, where the nymphs are about an inch and a quarter in length. The larger species of stonefly that inhabit certain rivers in the Catskill region are by far our biggest aquatic invertebrates.
Like mayflies, immature stoneflies are called nymphs when metamorphosis is incomplete because the immature insects quickly transform to adults without a pupation stage. And as the name implies, all stoneflies migrate to the shallows, climb out of the water and hatch on stream-side river stones or logs.
Our species include early brown stoneflies and little green stoneflies, which are on the small side, ranging from 1/4 to 3/4 of an inch. Then there are the larger species, members of the families Pteronarcyidae (salmonflies) and Perlidae (“golden” stoneflies). These insects range in size from one to two inches. Stoneflies are found in rivers with well oxygenated water and plenty of bottom detritus (dead leaves) to feed upon, although some species prey on other insects. From my observations, stoneflies do not appear to inhabit the upper reaches of our colder tailwaters. Instead, they’re found in most of our freestone rivers. For example, one June day, I found a rare, large daytime hatch of golden stoneflies along the Delaware River near Lordville, NY. Unfortunately, very few flies from that hatch ended up on the river, so there was no dry-fly fishing that afternoon.
From a fly-fishing standpoint, at least in the Catskills—a bit more irony, here—unless anglers happen to find a daytime hatch of large stoneflies, which is extremely unlikely, there is very little dry-fly fishing. However, the nymphs are recognized by trout and are greedily taken when dislodged from river stones. So, if fly fishers are interested in fishing with imitations of these large stoneflies, it means drifting big artificials along the bottom in those rivers where good populations are known to exist. Most anglers are not interested in this type of fishing because it is difficult, preferring instead to cast their dry flies to hatching mayflies and caddisflies.
Stonefly hatches in the Rocky Mountain West are a completely different phenomenon. Large, sometimes huge hatches occur during the day and are the most eagerly awaited emergences of the season. As in some of our rivers, there are several species of very large stoneflies. Some of the earliest to emerge are from the Perlodidae family, commonly known as spring flies. Spring fly hatches begin in March, when water temperatures reach or exceed 43 degrees and before runoff begins. Then about the fourth week of June, the salmonfly hatch begins. Salmonflies are also members of the Pteronarcyidae family, just different species than we see here in the East. Salmonflies are the largest of western aquatic insects. And like our green drakes, the hatches are spectacular—even more so. These huge flies hatch by the thousands and bring large trout to the surface, beckoning anglers from all over the country—even other countries. There are so many anglers and guide boats on western rivers during the salmonfly hatch that finding a place to fish can be a problem. Because of all the pressure, I’m not sure that the fishing is as good as the hatch. Salmonfly hatches begin in the lower reaches of western rivers where water temperatures are a bit warmer and move upstream over time. This hatching behavior provides anglers with the opportunity to follow the flies as they emerge upriver.
One afternoon, while studying at the University of Montana in Missoula, several of us were fishing the Clark Fork River, which flows right by the campus. It was sometime in March when I saw some large stoneflies on the water without a clue as to what the species could be. There was a rise mid-stream; I made a cast with a large dry fly and landed a nice Clark Fork brown. Later that same year, I caught the tail end of the salmonfly hatch on Rock Creek, which is about 20 miles east of Missoula and a tributary of the Clark Fork. I saw some huge rises but did not move a fish during that hatch.
Sadly, those two fishing trips amount to my total exposure to stonefly hatches in Western Montana. That being said, anglers who have the opportunity should definitely plan to fish these western stonefly hatches. The huge amount and large size of these insects, particularly salmonflies, that emerge during these hatches are spectacles that should not be missed—the fishing aside!