Stonefly · Pteronarcys californica
Salmonfly
Also called Giant stonefly, Pteronarcys.
Short answer
The salmonfly is a giant stonefly, two to three inches long and tied on hook sizes 4 to 8, that hatches on western freestone rivers in late spring. The hatch moves upstream a few miles a day, lasts about a week in any one place, and brings the largest trout in the river to the surface.
What a salmonfly is
Pteronarcys californica is the largest insect a western trout will ever eat off the surface — an orange-bodied, dark-winged stonefly big enough to be unmistakable from the bank. The nymph lives in fast rocky water for three or four years before crawling out onto a rock or a willow to hatch, which means the adults appear on the bank rather than on the water, and get blown back onto the river in numbers. The hatch progresses upstream as water temperature climbs, moving a few miles a day, so the same river can be finished at the bottom and not started at the top in the same week.
- Hook size
- Hook sizes 4 to 8
- Colour
- Bright orange underbody, dark brown-black wings and thorax
The stages trout eat
- Nymph
- Large, dark and clinging to rocks for three to four years. A Pat's Rubber Legs is one of the most useful flies in the West.
- Migration
- Nymphs crawl to the bank before hatching. For a week beforehand, fishing a big nymph tight to the edge is deadly.
- Adult
- Hatches on land, then blows onto the water. Trout look for them against the bank and under overhanging willows.
- Egg-laying
- Females return to the water to drop eggs, which is when the surface fishing is at its most frantic.
When does the salmonfly hatch?
| When | What is happening |
|---|---|
| Late May | First emergences on the lower, warmer reaches. The hatch starts downstream. |
| June | Peak, climbing the river. A week of it in any one place and the busiest guiding weeks of the year. |
| Early July | The upper reaches and the high-altitude rivers, as the last of the snowmelt clears. |
| Rest of the year | No adults, but the nymph is in the river every day of its three-year life and always worth fishing. |
Emergence dates move with latitude, altitude and the weather of a given year. Treat these windows as a shape, not a diary, and check a local report before you travel.
Where it matters
Western freestone rivers: Montana's Big Hole, Rock Creek and Madison, Idaho's South Fork of the Snake and Henry's Fork, Oregon's lower Deschutes, and Colorado's Gunnison. The Montana, Idaho, Oregon, Wyoming and Colorado pages all name it.
Fly fishing in Montana Fly fishing in Idaho Fly fishing in Oregon Fly fishing in Wyoming Fly fishing in Colorado
How to fish it
Fish the banks, not the middle. The adults are blown off the willows, so the trout are tight to the edge, often in water you would walk through. Use a heavier tippet than the hatch would suggest — 3X is sensible with a size 6 fly and a big fish. In the week before the adults appear, fish a large dark nymph right against the bank and you will often do better than the people who arrive for the hatch itself.
- Fish the bank. The adults fall off willows, not out of the sky.
- Arrive a week early and fish the nymph rather than chase the adults.
- The hatch moves upstream daily. Yesterday's report is already out of date.
Flies that imitate it
Each of these is a card in the deck, and each has a full page in Our Fly-brary.
Keep reading
- Dry fly vs nymph — which stage to fish, and when
- Why trout refuse your fly — usually the wrong stage, not the wrong pattern
- Best time of day to fly fish — the daily logic behind the table above
- Our Fly-brary — every fly in the deck, explained