Intro to Montana Stonefly Hatches

Only six types of Montana stonefly hatches are of any importance in the Yellowstone area, and two of these are only of minor importance. Moreover, Montana stonefly hatches take place almost exclusively on freestone streams, and are really only abundant in large, freestone rivers. To top it off, most Montana stonefly hatches are only of brief duration, with most species only hatching for a week or two in any one location. Despite these facts, stoneflies are of absolutely vital importance to anglers visiting the area.

The reasons for this are simple: of the four important species of stoneflies, three of them are the largest trout stream insects found in the region, sometimes reaching the size of an adult woman’s finger. and their nymphs mature in rivers for two or three years before adulthood. This means that they provide large meals for the fish, and they do so year-round. While everyone likes fishing dry flies, and the early summer hatches of two species of stoneflies rank as “bucket list” events for many anglers, stonefly nymphs rank among the most consistent flies you can use here.

All stoneflies require turbulent, well-oxygenated water with a bottom substrate comprised at least partially of large cobble and boulders. They also require water temperatures to go through wide swings over the course of the season. For these reasons, they primarily inhabit large, freestone rivers: the Yellowstone, Gallatin, Boulder, Stillwater, Gardner, and Madison between Quake and Ennis Lakes. There are also fishable but less important populations in rougher portions of the Lamar and its tributaries, the Lower Madison, the lower Firehole, the rougher sections of the Madison within Yellowstone Park, and rough portions of the Gibbon River. Small stonefly species, in this area meaning Yellow Sallies and Little Olive Stoneflies, also inhabit many small streams and faster-flowing sections of meadow rivers like the Lamar. Elsewhere, you should not expect to use any stonefly patterns, big or small.

Note that all stoneflies emerge in a different fashion than the vast majority of mayflies and caddisflies. Instead of drifting or swimming to the water surface, then emerging from their nymphal or pupal shuck and flying away, all stoneflies crawl ashore on bankside rocks or vegetation, then shed their nymphal shucks. They then mature in bankside vegetation before returning to fly over the stream for mating and egglaying. Stoneflies live for several days once they climb out of the river, longer than any other trout water insects besides damselflies and dragonflies.

Because of this life cycle, stoneflies are good choices in extremely shallow water (right next to the bank), while there is never a concentrated “hatch” of insects that gets the trout concentrated and rising consistently. Instead adult insects matched by dry flies are available when they fall out of streamside vegetation (again, right next to the bank), when they mate over the river (usually in the evenings), and when they lay eggs and drown. You can therefore expect to fish dries all day long when trout are keying on stoneflies, but you should not expect to find the fish concentrated or to find specific brief periods when lots of fish will be eating them. Instead, cover a lot of water and generally fish your stonefly dries tight to the bank except when you are seeing swarms of mating or egg-laying insects flying over the river.

Montana Stonefly Hatches Chart

The following table covers important stonefly hatches region-wide, from the most common and important insects to the least. Note that this is a general chart. Crucial insects on one body of water might be rare or even absent in others. Check the appropriate page under the Our Waters menu above for hatch charts specific to all area waters. In particular note the timing given on these dedicated pages: stonefly hatches are highly water temperature-dependent and so occur at very different times ranging from late May through late July or even early August depending on the river in question and the amount of winter snow. This is particularly true of the marquee Salmonfly and Golden Stonefly hatches.

montana stonefly hatches chart

Discussion of Specific Montana Stonefly Hatches

Salmonfly (Giant Black Stonefly, Pteronarcys)

Salmonflies, often called Giant Black Stoneflies or by their Latin genus Pteronarcys, provide not only the most famous Montana stonefly hatches but also the most famous hatch in the entire Yellowstone area overall. These insects are huge as adults and mature nymphs, often as long as an adult’s pinkie finger, and they hatch in profusion. While all stonefly nymphs can produce big trout, even dry Salmonflies can get some of the largest trout in the river to rise. Because of this fact, and just the sheer spectacle of so many insects the size of hummingbirds swarming bankside bushes, hitting a Salmonfly hatch just right is one of those events that anglers will keep talking about years later.

Salmonflies are unmistakable. The nymphs resemble prehistoric monsters, being dark brown to black in color, somewhat resembling aquatic cockroaches. Adults are orange and black with tan or gray wings with pronounced venation. They range from an inch and a half to three inches in length, and are best-imitated by #4 to #8 flies tied on 3xl hooks as adults, with #6 the best overall size for both nymphs and dry flies.

This is really the only insect where it’s common to use hook sizes slightly smaller than the real thing: some bugs are so big that they’d require a #1 4xl hook to match, and it’s basically impossible to get a dry fly that large to look “alive.” The orange abdomens are the most prominent feature of these bugs. Sometimes it’s very prominent and bright, other times it’s more rusty and dirty orange, but it’s always present.

The best Montana Salmonfly hatches in terms of consistency, distance in river-miles the hatch covers, and duration take place on the Madison between Quake and Ennis Lakes, the Gallatin from near Big Sky down to Gallatin Gateway, and the Yellowstone from the Lower Falls of the Yellowstone all the way to Emigrant, with fractured hatches from Emigrant to Livingston and beyond. The most consistent of these is on the Madison. The longest-lasting and most potentially “epic” is on the Yellowstone.

Additional Montana stonefly hatches of shorter duration and much shorter distance in terms of river-miles occur on the Madison within Yellowstone Park, the Lower Madison below Ennis Lake, the Boulder, the Stillwater, the Lamar River, the Yellowstone immediately downstream of Yellowstone Lake, the Gardner, and the Firehole. Fishable hatches do not occur on the Missouri River, any small streams, meadow streams or meadow sections of larger rivers, or spring creeks.

Hitting the hatch is the hard part: these bugs typically last only a week or ten days in one location, with areas with both geothermal and cold surface water inputs seeing hatches last somewhat longer. In a general sense Salmonfly hatches advance upriver as runoff recedes and water warms, starting at lower elevations and advancing upstream at a rate of several miles per day, with the speed of advance largely determined by air temperature and water level: if it’s hot out and the snowpack the previous winter was low, the river will warm at a similar rate from top to bottom and the hatch will advance upriver quickly or even pop almost everywhere all at once, while if air temperatures are cool and the winter was snowy, the hatch will be drawn-out and last a long time.

If you’re trying to plan to fish a specific Salmonfly hatch, be flexible: you want to come just as snowmelt recedes enough for a given river to be fishable. If you take the Yellowstone outside Yellowstone Park as an example, this might occur on June 15 following an extremely dry winter with a warm spring, or it might occur on July 10 following a wet winter and cold spring. Keep in regular contact with your chosen outfitter (preferably us) all through the spring to get a good sense on when to come.

Regardless of river or year, here’s a good general template to follow as far as tactics: Fish nymphs ahead of the hatch, meaning for the week or so before the hatch begins or upstream of the heaviest concentrations of adult bugs. Don’t hesitate to fish these right next to the banks, since as-noted all stoneflies climb out on bankside rocks when they emerge. Once adult insects are present, fish high-floating flies tight to the banks to imitate bugs that fall from bushes. Fish lower-floating or even drowned dry flies anywhere the water is turbulent to imitate egg-laying or drowned bugs. Continue to fish the drowned flies after the hatch is largely past to imitate the last, straggler insects.

The best dry fly fishing is usually for the first day large numbers of adults are present and after the hatch has begun to wane, since these bugs are so big and so numerous that the fish can and do become glutted on them and do not feed for a while in the middle of the hatch. Besides that, the peak of the hatch also sees peak traffic: some stretches of river will see 100+ guided parties on the water at the peak, almost all of them throwing Salmonflies, so the fish do get stung. Once the hordes have moved on, the fish go back to eating dries again.

Salmonfly nymphs are good choices all year. Our favorites are Minch’s Black Stones, Brown Girdle Bugs, and Double-Bead Bitch Creeks, particularly just before and during the hatch, since Salmonfly nymphs begin taking on an orange hue just before hatching and these orange-bodied patterns can also look like drowned adults. Black or Black and Orange Woolly Buggers can also be good right before the hatch.

Good high-floating dries, which are most effective in remote hike-in stretches of river (like the Black Canyon of the Yellowstone) or towards the beginning of the hatch, generally include foam components. Our favorite choices include Salmonfly Chubby Chernobyls, Mystery Meats, and Carnage Salmonflies. There are a ton of Salmonfly patterns that fit in this category, all of which work, so feel free to pick your favorites.

Good low-floating dries, which are most effective in water that sees heavier pressure and towards the tail end of the hatch when trout are looking for egg-laying Salmonflies, either lack foam or have it concentrated at the front of the fly so that all or a portion of the fly rests in or under the surface film, while still being visible to the angler. Our favorites are Parks’ Salmonflies, Gould’s Half Down Salmonflies, and Sunken Stone Salmonflies. Don’t hesitate to fish such flies completely wet, just barely visible four or six inches under the surface film. This can be particularly effective in turbulent water where insects that either fall in the water or get sucked down while laying eggs will never get airborne again.

Golden Stonefly (Trout Fly)

Golden Stoneflies are the Salmonfly’s smaller and less impressive cousin, hence the name “Trout Fly.” They live in exactly the same water as the Salmonfly and hatch about the same time. The trout like them almost as much, even though they generally hatch in slightly lower numbers and are certainly less noticeable than the giant Salmonflies. Whenever you are seeing Salmonflies, you should also expect Golden Stoneflies. If the trout are ignoring your Salmonfly, fish a Golden Stonefly instead. It’s often a good idea to double up: fish a Salmonfly nymph with a smaller Golden Stone pattern behind it, or fish a Golden Stone nymph as your dropper below a dry Salmonfly.

In other words, the Salmonfly and Golden Stonefly hatches should really be considered the main Montana stonefly hatches taken together, rather than treated separately.

Note that the fly often called a “Late Summer Golden Stone,” especially by old-timers, is in fact a Nocturnal Stone. This fly has different habits and looks quite a bit different than a true Golden Stone.

Adult Golden Stoneflies are predominately golden yellow in color, as their name suggests. Their wings are paler than those of Salmonflies, usually translucent silver or cream. They range from #6 to #12, again on 3xl hooks, with #10 the single best size.

As with Salmonflies, Golden Stonefly nymphs can be good choices year-round. In addition, there’s a lot of overlap between flies that match the Golden Stone and flies matching assorted other insects. Many Golden Stonefly patterns could be mistaken for large caddis larvae, other species of stoneflies, or even sculpins (minnows) or drowned grasshoppers. This is true to a lesser extent for dry flies, which could be taken as grasshoppers, Yellow Sally stoneflies, or even large caddis in addition to Golden Stoneflies.

Because of the overlap, we generally suggest impressionistic flies rather than exact imitations. Our favorite nymphs (by far) are Minch’s Golden Stones and Tunghead 20-Inchers. You can also do well on more-exact nymphs, particularly on the Madison. Our favorite is the Lex’s Golden Stone. Good dry flies include gold Chubby Chernobyls, Gould’s Half Down Golden, Turck’s Tarantulas, gold Carnage Attractors, the classic Yellow Stimulator, and Carnage Golden Stoneflies.

Midnight Stone (Nocturnal Stone or Brown Stone)

Often thought of as a type of Golden Stonefly, the Nocturnal Stone is actually a very different animal. As its name suggests, it tends to hatch out at night and is almost never seen flying during the day, not least because the males are flightless. Nocturnal stoneflies provide the longest-duration Montana stonefly hatches, often continuing for six weeks or so at a slow boil.

Nocturnal Stones hatch later in summer than other stoneflies, beginning just as the Salmonflies and Golden Stoneflies are tapering off. They do not hatch in profusion for a short period of time as do other stoneflies, but string themselves out for several weeks, even a month or more, hatching in small numbers between sometime in early July through at least early August, and often into September. You will seldom see adult Midnight Stones even if you hunt for them. Instead you’ll find a nymphal shuck here or there. Because of these facts, Midnight Stones do not attract concentrated attention from either the fish or anglers. Instead, imitations of this insect (nymph or dry) make good searching patterns when you’re covering a lot of water, either on foot or from a boat. They’ll draw opportunistic fish, often big ones.

The Yellowstone River from Gardiner to Big Timber, the Stillwater River, the Boulder River and the Madison between Quake and Ennis Lakes produce the best fishing with these insects. I hesitate to say “best hatches” because there are almost never enough of these bugs around at any one time ton constitute a hatch. It’s just a function of how often the fish are willing to look up for a Midnight Stone imitation compared to something smaller.

As adults, these are tan and black insects running about #6 to #10, always on 3xl hooks. Some also have gold markings. Nymphs should be tan and black or peacock-bodied. Since adult Midnight Stones look a lot like grasshoppers, it’s a good idea to use crossover patterns. Large Turck’s Tarantulas and tan or gold Chubby Chernobyls are good choices, but really any #8 or #10 rather drab-colored dry fly might be taken as a Midnight Stone (or a grasshopper). Nymphs are generally more productive than dries and should be fished in #8 through #12. Good nymphs are tan and black Girdle Bugs, 20-Inchers, peacock-bodied Mega Princes, and assorted patterns marketed as “brown stones.” These are often extremely effective when fished on very long (3-4 foot) droppers beneath huge dry flies.

Yellow Sally (Little Yellow Stonefly)

Yellow Sallies, comprised of two species of small yellow to yellow-green stoneflies, one basically size-14 and predominately yellow and one basically size-16 and often featuring a faint chartreuse tinge, are by far the most widespread stoneflies in the area. They are the only type of stoneflies that can be found in fishable numbers on meadow-type streams like most of the Lamar River and its tributaries and the upper Gallatin River. They are also common on many small streams. They are still basically absent from the Firehole and Missouri Rivers and spring creeks, as well as lakes. Anywhere they are present, Sallies begin hatching about the same time as Salmonflies and Golden Stoneflies (basically just after the spring runoff recedes) but last longer, usually about a month overall.

Though their overall size and coloration differ slightly, the two species of Sallies are generally matched with the same patterns, hatch from the same waters at the same time, and draw about as much interest from the fish.

Dry Sallies seldom get the fish very excited, but are good changeup choices particularly on waters where the trout are glutted on Salmonflies and on smaller streams, where they are sometimes the most widespread insects during their emergence period. Otherwise, their importance to the trout is spotty, differing from spot to spot, day to day, and especially year to year. Some years we have fantastic fishing with Yellow Sally patterns on the Yellowstone, other years we have had clients catch almost nothing on them, for example. Regardless of locale and general importance, you are most likely to do well on Yellow Sallies in late morning or early afternoon, particularly just downstream of riffles, since egg-laying and mating flights take place in these locations.

Nymphs are much more important than dries. They make excellent dropper nymphs through the entire hatch cycle and often well into August as well, probably because there’s a bit of crossover between most Yellow Sally nymphs and mayfly nymphs, as well as some caddis pupae.

Note that all Yellow Sally adults have faintly translucent abdomens. As the female insects mature, these abdomens begin to take on a faintly pink, orange, or red hue due to the developing eggs inside. Effective patterns often match this with either a reddish tail or back half of the body.

Good nymphs to match Yellow Sallies are my Amber Prince (which doubles as a caddis pupa), beadhead Baby Golden Nymphs (also called the “Boss Hogg”), and especially the Montana Sally, a heavy wire-bodied nymph often tied jig-style. Always fish Sally Nymphs as droppers under attractor, large caddis, or Salmonfly/Golden Stonefly dry flies (if fishing shallow) or with a larger stonefly nymph (if fishing deep). Our favorite dries are yellow Krystal Stimulators and pink Clacka Caddis if we think trout are taking Sallies only opportunistically and Goldie Hawns if we think the trout are keying in particular on Sallies.

Little Olive Stonefly

Little Olive Stoneflies hatch at about the same time and from the same water as Yellow Sallies. They are also about the same size. In fact, the only key differences are that they are dark olive in color and not as numerous. They are only occasionally important to the angler, but we find that when the fish do happen to be eating these bugs, they do so very particularly and aggressively. Therefore it’s important to always carry a few #14-#16 Olive Stimulators if you’re fishing freestone rivers in June or July. These are the only dry flies we use to match this insect.

We have had the most success with these flies in June on the Gibbon River and in July on Slough Creek, but have also had good fishing on assorted small streams, the Yellowstone, the Lamar, and Soda Butte Creek. One key benefit of these insects if you do encounter them is that most anglers and guides do not match this bug, so the fish will probably not be too suspicious of flies matching it. We don’t know if the trout ever key in particular on the nymphs of this fly, but #14 to #16 Olive Montana Princes (wire-bodied rubberleg Prince Nymphs) probably match it if they do, and work well as attractor nymphs in a general sense, too.

Winter Stone (Tiny Black Stonefly)

As the name suggests, these small (#18) black stoneflies hatch in late winter, primarily on the Yellowstone and Madison Rivers, where they are often seen in melting snowbanks. They are most common in March but may be spotted earlier as well. We don’t know if the trout ever key on this insect. If they do, odds are dark-colored mayfly nymphs and black midge dry flies are close enough, and also work to match the more-common late winter insects.