The venerable king of all hatches in Big Sky Country, the Salmonfly Hatch lives in infamy among fly anglers world wide. Nothing generates more excitement, for both fish and fishermen alike than salmonflies, and with good reason. The chance to see a wild trout rise to the surface and inhale a three inch long insect (or better yet, your three inch long fly) is the stuff that fly fishing dreams are made of.
Salmonflies are not unique to Big Sky Country. Pteronarcys californica (Tare-uh-nar’-sis cal-uh-for’-nuh-kuh) is found throughout the American West, and its diminutive cousins are found across North America. What sets Big Sky Country apart from other areas is how long the bugs are active during our season. From Mid-May through the end of July you can find salmonflies somewhere within striking distance of the Big Sky Anglers World Headquarters in West Yellowstone, Montana.
Timing this hatch from year to year on a particular river can often be an exercise in futility. On dry years it’s early. On wet year’s, it’s late. When the weather is hot, the hatch moves quickly upstream. When the weather is cold and wet, the hatch stalls out. Generally speaking, we see the first big bugs of the year in mid to late May on some of the area’s warmer waters like the Henry’s Fork and Firehole. As the activity is winding down on those rivers, we start to look to the Madison. Finally, we turn our attention to the high country, and rivers like the Yellowstone and Gallatin which are usually the last to warm up and clear from run off.
Everything about this hatch is big. The bugs themselves are massive. Mature salmonfly nymphs have two stout tails, a dark chocolate brown coloration, and can reach a length of nearly three inches. Fly imitations are a whopping size 4-6.
It takes 3–4 years, a virtual eternity in bug years, for the nymphs to reach their impressive size. This means that there are always multiple year classes, and multiple size classes of nymphs in the river at any given time.
The volume of insects can be staggering. Nymphs migrate to the stream bank of select areas in preparation to emerge, and it’s not uncommon to find handfuls of them under a single rock along the bank. To emerge, mature nymphs will crawl out of the water (usually at night) onto riparian rocks and vegetation to molt into winged adults. When conditions are right (warm, sunny, windy), clouds of adults swarm upstream in tremendous mating flights.
Salmonflies love big water. These studly bugs require a ton of oxygen, and they’re well-equipped with large, strong appendages to hang in rough, turbulent water. Luckily, from the Madison’s fifty-mile riffle to canyon sections on the Henry’s Fork, Yellowstone, Firehole, Gallatin and many more, we have no shortage of this type of water in Big Sky Country.
Big fish love these big bugs. On several area rivers this is one of the very few times of the season that you can find the largest fish of the system feeding aggressively.
All these big bugs and big fish can also draw some of the biggest crowds of the season. Boat ramps and fishing access sites fill to capacity as guides and anglers hope to catch the hatch just right. As the hatch moves upstream through a system there’s an imaginary line of “good fishing” that moves with it. Ahead of the line, the fish aren’t looking for the adults yet, but are keying on the nymphs. Behind the line, every fish is gorged on adults like a family sitting on the couch after a gluttonous Thanksgiving dinner, and not feeding. Further behind the line, fish have had some time to digest, and start to head back for second and third helpings.
The salmonfly hatch epitomizes everything in Yellowstone Country that anglers dream about - big landscapes, big rivers, big fish, and big hatches.