Parks' Fly Shop: Guide to Yellowstone Area Stonefly Hatches, Yellowstone Hatch Chart

Guide to Yellowstone Area Stoneflies

Of the "big three" families of insects important to trout in our area: mayflies, caddis, and stoneflies, stoneflies are the least important in duration. When they emerge, however, they are usually the most important flies on the water. The following guide includes general descriptions of the physical characteristics, flight times, and seasons of emergence for the most important stoneflies in the region under the purview of our Trip Planner. Suggested patterns are also given. Individual hatch guides for the most prominent streams in the area, with individualized season information and flight times, are given on the appropriate page in the Our Waters section of the site.

The most important things to remember about stonefly emergences in general are:

1.) All stoneflies crawl to the bank to emerge, meaning there's no such thing as a "stonefly emerger."

2.) Adult stoneflies are available to trout when they fall off streamside branches they're resting on, meaning casts have to be close to the bank, when they hover over the river during mating flights, and when they return to lay eggs.

3.) Nymphs draw tremendous action for some weeks prior to the hatch for the larger, more-important species, provided the water is clear enough.

Please contact us for more information on area hatches and the flies to match them.

The first portion of the following guide consists of an emergence table and notes. The second portion consists of longer descriptions of each listed insect.

Yellowstone Area Stonefly Emergence Table

Table Key: X=primary hatch period, x=secondary hatch period, blank=no hatch
Name Description Active Time Emergence Month
      Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Salmonfly Very large, orange and brown/black body with well-marked tan/clear wings. #2-8 2-3xl Usually afternoon to evening, but bugs falling from bushes are always gobbled up.         x X X x        
Early Summer Golden Stone Golden brown with yellow highlights. Slighly smaller than the Salmonflies. #6-10 2-3xl. Same as Salmonfly, but not in swarms that are as large.           X X x        
Yellow Sally (Two Species) Creamy yellow to pale neon green bodies. Egg sacks and lower intestines are bright red and often visible. Wings cream. #14-16 3xl, #12-16 standard. Late morning through evening.           x X X        
Little Olive Stone Olive body, tan wings. #16 Stimulator is what you need. Late morning through late afternoon.         x X x          
Late Summer Golden Stone (Midnight Stone) Tan and brown, large, usually the shucks are seen rather than the insects. #4-10 2-3xl. The name should be a clue... very occasionally one will be seen flying early in the day.             x X x      
Snowfly Black with pale tan wings. Small. #16-18 standard. Afternoon.   x X x                
Summer Black Stone Short dark tan wings, black body. Runs around on shore like its on a caffeine rush. #12 3xl. Unknown             X          

Discussion of Insects

Boldface type indicates fly patterns. Italics are used for scientific names.

Salmonfly (Giant Black Stonefly)

Pteronarcys californica

The Salmonfly is probably the most well-known hatch in the entire Rocky Mountain region, and Yellowstone-area rivers are home to some of the best hatches. The Yellowstone sees a trickle as far downriver as Columbus, with the core of the hatch from Emigrant upstream all the way to the head of the Grand Canyon, well into the Park. There are a few in the reach between the Lake and Upper Falls, as well. The Gardner and the Lamar (in its canyons) also see excellent hatches, with spottier emergences on the Madison in the Park and in the Firehole Canyon. Outside the Park the Madison sees a good hatch in the 50 mile riffle. Except on the Yellowstone, Madison, and Gardner, this is a brief hatch, lasting no more than a week. On the Gardner it can stretch to two weeks and three on the Yellowstone.

Salmonflies are impossible to mistake for anything else. Salmonflies are large, orange and black or orange and dark brown insects that vaguely resemble locusts. At the peak of the hatch, there are enough mating insects in the air to fill the sky. The hatch tends to move upstream, though in recent years the progression has seldom been orderly, with bugs instead hatching in fits and spurts over several reaches of river at once. The best fishing is found by nymphing immediately ahead of the hatch.

Nymphs you should carry are the Minch's Black Stone, the Double-Bead Bitch Creek, the Brown Girdle Bug, and the Bitch Bugger (which is a streamer-Salmonfly combo). Of these, the Black Stone should be your go-to fly, especially on the Gardner. The dry fly fishing is best at the forefront of the hatch or behind it, because the peak frequently finds too many fishermen on the river and the fish either glutted or hook-shy. The best dry flies are: Wiese's Prom Queen Salmonfly and Roman's Thing from Uranus in foam patterns and the Parks' Salmonfly and Gould's Half Down Salmon in "fur and feather" patterns. I carry one of each, since the primary benefit of foam is its flotation, but you sometimes want a Salmonfly to sink. They don't float well themselves, and egg-layers and others frequently get waterlogged and sucked under slightly. Imitating this is not possible with foam. The Half Down is better late in the hatch because it imitates an egg-layer, while the Parks' works at any stage because its thick hackle suggests a fly trying to get airborne again.

Salmonflies are creatures of fast water and emergence times vary by several weeks due to differences in water temperature and level, so keep your eyes on our Fishing Report to know when to expect the hatch on a given body of water.

Golden Stonefly

Hesperoperla pacifica

Golden Stones are almost as large and almost as important as Salmonflies, but they don't have the same following. This is largely because Salmonflies all hatch in one push while Golden Stones have an initial strong emergence at about the same time as the Salmonflies but continue to hatch sporadically for a couple weeks. This gives the trout a lot more time to feed on them, but less of a mystique.

Good patterns for the Golden Stone emergence match those for the Salmonfly except in size and color, with golden-tan patterns in size-8 or 10 the best dry options and Minch's Golden Stone the best nymph. My favorite dries are Gould's Half Down Golden and Trina's Carnage Attractor Golden. Attractor/terrestrial patterns like Yellow Stimulators, Chubby Chernobyls, and Turck's Tarantulas also match this fly to a large degree. Indeed, many popular hopper patterns probably owe as much of their success to matching Golden Stones and Midnight Stones as to matching grasshoppers. One difference between Golden Stones and Salmonflies in our area is that Golden Stones thrive in the Gibbon Canyon, while there are only a handful of Salmonflies there.

Yellow Sally

Genus Isoperla

Yellow Sallies are generally size-14 or 16, making them the midgets of the summer stoneflies. They hatch to a degree from almost all streams in our area, including small meadow streams like Soda Butte Creek, which otherwise lack significant stonefly populations. Like Golden Stones, they typically last six weeks or so in varying numbers. Though Sallies are not a marquee hatch, trout will sometimes key on them, even when Salmonflies or large mayflies are present, so it's always a good idea to carry some. To imitate non egg-layers, a small Yellow Stimulator is as good as anything else. For the egg-layers, a small Elk Hair Hopper or Korn's Sally Tweeter works well in fast water because it floats well, while in slower water a dedicated Sally pattern such as the Goldie Hawn is a better choice. A yellow Copper John is a good match for the nymph.

Little Olive Stone

Scientific name unknown.

All you need to know is that if you're fishing the Gibbon in mid-June, you've got to have some #14-16 Olive Stimulators. It's a good idea to have some on the Yellowstone and in the Lamar drainage in mid-July, as well, but they're not critical there are they are in the Gibbon Canyon.

Midnight Stone

Scientific name unknown.

This is why hoppers work before there are too many hoppers bouncing around the shoreline of the Yellowstone. This is a Golden Stonefly (really more of a mottled tan and black) that crawls out at night and mostly hides out during the day. Sometimes you do see them flying around, but the trout sure look for them. This isn't surprising given that they're at least as big as the early summer Golden Stones, and sometimes as big as Salmonflies. When you see split and empty nymph shucks on boulders just above the water in late summer, you know these guys are around. Use multi-role patterns like Chubby Chernobyls, large gold GFAs, and Turck's Tarantulas rather than any dedicated pattern for the dry, since there are so few of them around at any one time. Minch's Golden Stone is the nymph.

Snowfly (Winter Black Stone)

Scientific name unknown.

One of two bugs often called Snowfly, the other being a midge that's remarkably similar in coloration. This insect is small and black with light wings, and may sometimes get fish active in February or March.

Summer Black Stone

Scientific name unknown.

With so much food in the river at the time the handful of these bugs stumbles out, right around the Salmonflies, Golden Stones, tons of caddis, Green Drakes, PMDs, and Epeorus, you don't need to imitate it. A #10 Coachman Trude would be close enough if you felt the need.

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