Montana’s Classic Stonefly Bench: The Skwala, the Golden Stimulator, and the Little Yellow Stone
Series: Montana’s Classic Stonefly Bench — Article 3
Most fly fishers think the stonefly season begins when the salmonflies show up in late May and ends sometime around the Fourth of July when the hatch moves off the big rivers and into the high country. They are wrong on both ends.
The stonefly season in the American West begins in February.
While the rest of Montana is still arguing about whether it’s worth driving to the river, the Skwala is already hatching on the Bitterroot, the Clark Fork, and the Blackfoot. Skwala americana — a dark olive-brown stonefly roughly half the size of a salmonfly — crawls out of the gravel, climbs the bankside rocks, and starts showing up on the water before most fly fishers have pulled their rods out of the closet. The fish know. They’ve been waiting since October for something large enough to bother rising to, and the Skwala is large enough. In March on the Bitterroot, a size 8 Skwala dry on a short leader over the right bank structure will catch fish that have every reason to refuse it and not enough experience yet with what fly fishers are doing to know better.
The stonefly season also doesn’t end in July. The golden stonefly hatch — Calineuria californica and Hesperoperla pacifica — runs through July and August on rivers across Montana, Idaho, and Wyoming, quieter and less dramatic than the salmonfly event but often more fishable because the crowds have gone home. And behind the goldens come the little yellow stones — the Chloroperlidae, the yellow sallies, the small pale stoneflies that most anglers walk past without recognizing — hatching through August and into September on rivers that are otherwise considered post-season water.
Three hatches. Three patterns. Six months of stonefly fishing that most people leave on the table.
This is Article 3 of Montana’s Classic Stonefly Bench. Articles 1 and 2 covered the salmonfly patterns that define May and June. This article covers everything else — the early season nobody fishes, the mid-season hatch that outlasts the crowds, and the late-season opportunity that extends dry fly fishing into September on water you’ll often have entirely to yourself.
Table of Contents
The Stonefly Calendar Nobody Follows
Understanding when each hatch happens and where is the difference between planning a season and stumbling into one. Here is the practical western stonefly calendar, river by river:
Skwala Hatch — February through April
- Bitterroot: Late February through March
- Clark Fork: Early March through April
- Blackfoot: Mid-March through April
- Rock Creek: Late March through April
Golden Stonefly Hatch — June through August
- Madison: Late June through July
- Gallatin: July through early August
- Yellowstone: July through August
- Henry’s Fork: Mid-July through August
- Most smaller Montana tributaries: July through mid-August
Little Yellow Stone Hatch — July through September
- Present on virtually every Montana river during midsummer
- Peak activity late July through August on most drainages
- Often the only surface activity on low, clear late-season water
The angler who understands this calendar doesn’t have a salmonfly season. They have a stonefly season that runs eight months out of twelve, on different rivers, with different patterns, and with dramatically different fishing pressure at each stage. The Skwala hatch happens on uncrowded water in cold weather. The little yellow stone hatch happens on late-season rivers when most anglers have convinced themselves the dry fly fishing is over. Both are opportunities the stonefly calendar hands you for free if you’re paying attention.
