Every year, anglers all over this great land eagerly await the largest fly hatches of the season. In the East, particularly in the Catskills, fly fishers wait for the green drake hatch, which occurs right around Memorial Day. 

On Michigan’s Au Sable River, anglers get ready for the hex mayfly (Hexagenia limbata) hatch. 

In the Rocky Mountain west, it’s the salmon fly hatch that brings fishermen to the region, hoping to land the trout of a lifetime. 

Unlike green drakes and hexes, which are mayflies, salmon flies are members of the order Plecoptera, the stoneflies. These very large aquatic insects are classified as Pteronarcys dorsata. 

They take three years to achieve maturity, spending all that time as nymphs in various stages of development. Hatching begins about the last week of June, and moves upriver in relation to water temperature as emergence progresses. Because of this type of hatching behavior, anglers can follow salmon flies, extending their fishing several days.

While green drake and hex hatches are spectacles to behold in their own right, no other insect can match salmon flies, because of their very large size and sheer numbers. Adults are over two inches long—a very big mouthful for even the largest trout. 

Green drakes and hex mayflies hatch at dusk and after dark, making sight-fishing difficult, while salmon flies emerge during the day. 

Hatching begins in the late morning, after the insects have migrated shoreward; at that point, they climb out of the water and leave their nymphal cases. There are excellent hatches on the Madison, Bitterroot and Big Hole Rivers and on Rock Creek in Montana, and on the Henry’s Fork River in Idaho. These are not the only rivers where these giants of the aquatic insect world thrive, so anglers should check with local fly shops if they intend to fish the salmon fly hatch in other parts of the West.

Of all the years I spent in Montana, at the university in Missoula, I caught the salmon fly hatch just once. That was because most years, classes ended before the hatch began, and I was on my way back to New York for the summer. Fortunately, during my final year, I stayed in Montana for the entire summer, in order to complete a degree in aquatic biology. At the end of June, a friend and I went to Rock Creek, which is about 25 miles east of Missoula, to see if there were any salmon flies still around. 

I had fished Rock Creek many times in the past, mostly in the fall, but also in late May when the trout season opened. The early-season trips involved high, off-colored water, due to snow melt. There was no fly fishing. Instead—and I’m a bit embarrassed to write this—we collected salmon fly nymphs from the river bottom and used the large, immature insects as bait. That practice was perfectly legal at the time, and it was possible to catch a limit of trout very easily using this method. Montana has since stopped anglers from taking salmon fly nymphs from trout rivers as bait. 

On the morning of that late June day, so many years ago, we caught the tail end of the salmon fly hatch. We were well up Rock Creek before we found the flies. There were not so many adults around that would land on our arms, hats and even in our mouths, but there were enough. 

I recall standing by the side of the river and watching the hapless females fluttering about, going through the egg-laying process. Enough of the large insects ended up on the water to bring huge, slashing rises from some very large trout. 

For whatever reason, the flies we were using to imitate the adults failed to bring any strikes. I don’t know if it was because of our particular patterns, or if the trout were full of salmon flies. Anglers need to keep in mind that with all the large-fly hatches we fish—whether it be green drakes, hexes or salmon flies—even a three- or four-pound trout can eat only so many of these very large insects. 

That’s why it is important to be on the water as soon as these hatches begin, rather than later in the day or in evening when feeding may be over, the trout satiated.  

For those anglers inclined to fish before or after the salmon fly hatch, nymph-fishing with large imitations can be very rewarding. Because these insects take three years to mature, there are always some nymphs of one generation or another available for hungry trout. I used a large black salmon fly nymph that I purchased from Bob Jacklin’s fly shop in West Yellowstone, MT, several years ago. I was fishing the Madison River, just outside Yellowstone Park, at the time and hooked a very nice brown while bouncing a big salmon fly nymph along the bottom.

Like the green drake and hex hatches, the salmon fly hatch is an event every serious angler should plan to observe. It is an absolutely natural phenomenon found only in the aquatic insect world and in the western United States. I’m willing to bet that once you arrive at a river where the salmon fly hatch is in full swing and see tub-size rises, your hands will tremble while tying on a very big dry fly!