Stoneflies – A Fly Fishermen’s Guide to Fly Fishing’s Most Exciting Hatch

Fabled fly fishing moments and the best that the sport has to offer is often focused around hatches, breathtaking migrations, or epic moments where mother nature and fly fishing converge on simultaneous paths. The sardine run in Mexico, where every stripped marlin for hundreds of miles congregate and eat flies off the beach, and the blood worm hatch in the keys will make even the most stubborn tarpon lose their minds to name a few. In the American West, stone fly hatches on rivers in Colorado, Idaho, Montana and Wyoming is the pinnacle of iconic American fly fishing.

Stoneflies make up a significant portion of a trout’s diet. They are critical to fish growth. There are many different species of stoneflies worldwide. We will cover how they hatch, where they hatch, and why they are important to both fish and anglers. We will highlight the positive aspects that these aquatic insects have to offer, and touch on some of the realities of stonefly hatches. This will allow anglers looking to experience a stonefly emergence to set realistic expectations. At the end of this article, my hope is that you have a better understanding of fishing various stonefly hatches, and how to capitalize on some of the best fishing of the year.

What are Stoneflies?

Stoneflies are large or small winged aquatic insects. They are part of the order plecoptera, also known as stoneflies. They are a critical part of the ecosystem, and offer trout a high calorie meal year round, although active hatches happen between March and September depending on the species. They come in all different sizes, from tiny yellow sallies to gigantic salmon flies. They are crawlers. Spending the majority of their lives under rocks. However, they are sporadically and inadvertently pushed into the river’s current throughout the year, so fish will eat them any time they are given an opportunity to do so. That being said, the majority of the time they remain un-available as a significant meal for fish.

Stoneflies can reach enormous sizes for aquatic insects (up to 3 inches). A stonefly nymph has two antenna, two long tails, 6 legs, and a segmented armor like body. They are usually found under rocks in rivers. They can be black, brown, olive or yellow. Once they hatch, they grow two pairs of long flat clear wings. Unlike caddis, that also have downward laying wings shaped like a upright pup tent, stoneflies have wings that lay flat to their bodies. They are awkward fliers. Often times during a hatch, they fly clumsily around in the air and crash to the water’s surface to lay eggs.

The Stonefly Life Cycle

Female and male adult stoneflies, mate in stream side bushes. The female develops a dark black egg sack on the end of her abdomen. She takes flight to return to river’s surface. Landing on the surface of the river, she deposits her eggs. The eggs sink to the bottom of the river. The egg sack contains a sticky outer coating that allows it to adhere to river rocks. Stonefly nymphs hatch after 2-3 weeks. Crawling under rocks for shelter, a stonefly nymph, depending on the species, will spend 2-3 years developing during the nymph stage. It should be noted, that similar to a mayfly, stonefly nymphs require highly oxygenated water to thrive.

Stoneflies are some of the first large insects that you will see on the river in early spring or early summer. Once fully developed in the nymphal stage, it will be time for emergence. The key water temperature that fly anglers should look for as the colder months start to warm is 46 degrees Fahrenheit. This magic number is what coaxes the first stonefly hatches (Skwalas) of the year to migrate from river bottom to stream side banks. Stone flies are poor swimmers, as a result, they have adapted by crawling along the bottom of the river to the banks. Once out of the water, they can be found in all different types of vegetation. Their favorite place to find shelter is in tall stream side bushes where they will molt and shed their nymphal skin.

Even if there aren’t visible stoneflies in bushes or grass, fly anglers can discern that the hatch is happening by examining stream side rocks, concrete bridge trusses, and boat ramp structure. There will be nymphal shucks stuck to the various stream side structure. The shucks appear similar to locust shucks found in yard. At first, there will be a few on stream side structure. As the water warms, there will be more and more. This is the first clue that the hatch is on it’s way. I have fished the stonefly hatch many times, and unlike mayflies, the hatch is very predictable in that it always moves up stream. Slightly creeping further and further upstream day by day it is rather easy to predict what section is going to fish best if you spend consecutive days on the river.

Stream side, the nymphs will cycle through their final molt. Once out of the nymphal shuck, they must expand and dry their wings. They will spend one to two days in the bushes, and it is during this time that they must find a mate. The female develops a large egg sack on the end of her abdomen. Once fully formed, she will take fight and return to the river’s surface to drop the egg sack. It will sink to the bottom of the river and the lifecycle will start over.

Stoneflies are poor fliers, and they appear to flutter rather then fly. This is an advantage to the fly angler, because much of their adult life is spent crashing to the rivers surface, and then running back across the surface of the water to the river’s banks. This is visible by a large wake thrown out from stoneflies running on the water. Big trout key in on the surface action caused by the running behavior. It will often result in a feeding frenzy with fish gorging themselves on the larger insects and explosive strikes. Casting a fly pattern to the bank, and using your rod tip to skate a foam fly can result in lots of fun top water fishing.

Moments of Vulnerability

No matter what hatch you are trying to fish, in my opinion it is always best to break the hatching insect down into moments of vulnerability. Moments of vulnerability are periods of time during the hatching process when insects are most available to trout, or when the insect is most helpless during the lifecycle. This makes hatches easier to understand, and allows me to focus on specific fly fishing techniques that will result in more fish caught.

For starters, stoneflies spend most of their lives underwater and under rocks. As we mentioned before, they are poor swimmers. Throughout the year, they will haphazardly experience natural drift. This is the result of accidentally being caught in swift currents, or most species will purposely drift to change locations to increase genetic diversity. They are such a large calorie meal, that stonefly patterns can be fished year round even in colder months. They are rarely passed upon by fish.

The first real opportunity of vulnerability is when water temperatures start move into the high 40’s or mid 50’s. This will prompt mature stonefly nymphs to attempt their migration to the shore. Large amounts of nymphs will be knocked free from the river’s bottom and float at the same speed of the current of the river. In addition, as the water warms a fishes metabolism speeds up to create a perfect storm of feeding frenzy. The reward and desire for calories is so high, that big trout and little trout alike will leave the safety of prime lies and follow the crawling stone flies to the banks.

Before you see mature stone flies on the surface of the river, you will start to see sporadic evidence of their shucks on river side structure. This is a a sure sign that stonefly nymphs are starting their migration to stream side vegetation.

It is at this moment, that anglers should be ready to nymph deep along banks. Grassy banks produce more fish, because that is a stoneflies preferred habitat. Not all banks will fish hot, and the goal here is to fish and move, fish and move, until you find a hot bank. The trout will follow the food, and the pre hatch migration of stonefly nymphs will have the trout following them to the banks of the river.

Most of the biggest trout of the year will be caught during this time. This is the first real opportunity for fish to eat stoneflies in large numbers. In addition, this process starts in spring and early summer. Trout have been in a state of hibernation for the last 5-6 months during the coldest months of the year. Their only sure source of protein has been tiny midges. Large stoneflies are a welcome meal. Spring time is spawning season for rainbows and cutthroat trout, and they are in desperate need of calories for the mating process that lays ahead of them.

Stone Fly Fishing Rig

You will most likely be fishing banks with structure close by. Use heavy gear to reduce break offs. Stonefly imitations tied on large hooks and fished 6′ to 7′ feet under a strike indicator with 2x tippet allows anglers a better chance to land big fish. I prefer to use a 7.5ft 2x leader, and then add 1.5′ of fluorocarbon tippet to the leader. There are number of stonefly flies that work well, but my preferred point fly is a size #4 or #6 orange and brown rubber leg. I also prefer a stonefly pattern tied double heavy with lead or a tungsten bead over a lighter one fished with split shot on the leader. My preference with fishing rigs, is the less the better, so if I can remove the split shot and just use heavy flies it makes fishing easier. Sometimes, I will fish two rubber legs in tandem if the “turd” bite is hot. The key is to fish tight to the bank and cover.

There is an old saying, that if you aren’t losing flies this time of the year in the bushes, then you aren’t fishing close enough. This is a true statement, since the fishes food source is on the banks actually crawling out of the water, this leaves fish with very little shelter from predators and few places to get out of the current and conserve energy. The result, is that fish will sometimes almost be on dry land, underneath overhanging bushes and primarily beneath unseen cut banks a foot or two below the water.

The Walking Mend

It can be difficult to get a long leader close to the shore. An old guide by the name of Rod Bowden, that guided many years for the outfitter I worked for, Worldcast Anglers, showed me a trick on a training day. He called it the walking mend. It works well out of a drift boat or raft, and if you aren’t the best caster, it will save you a from losing a ton of stonefly patterns in steam side bushes.

To perform a walking mend, you make a cast close to the bank, but a few feet outside of where you want the fly to land. Then using the tip of the rod, you make a series of half mends that are similar to half powered roll casts. The forward momentum of the fly line pulls the indicator several inches out of the water and propels it towards the bank and bushes a few inches at a time. Three or four of these half powered mends will gently walk the indicator closer into the bank and directly into feeding lanes.

Swinging Stonefly Patterns Under Bushes

Swinging stone fly patterns is a deadly tactic when the bite is hot. Try this and you will be pleasantly surprised at how many fish you will catch. Often these are the biggest fish in the river, as you are purposely swinging the stonefly nymph pattern into prime lies that other anglers are passing by.

Swinging stonefly fly patterns can be done with both nymph rigs fished under and indicator or with a dry dropper. I prefer the dry dropper rig, as it is less to handle, and thus easier to cast and swing. My preferred rig here is a 6′ to 7′ 2x mono leader with a larger size foam dry fly as my point fly. The chubby chernobyl is my personal favorite. A size #4 or #6 chubby properly dressed will float just about any nymph fly that you want, even in heavy pocket water. My preferred nymph is a Pat’s Rubber leg. Early season, I go with a larger size #4 or #6 when the Salmon flies are hatching. Mid summer I down size to #8’s and #10’s when smaller golden stoneflies are hatching. Attach a 2-3 foot piece of tippet to the bend of the hook of the chubby using a clinch knot. Then at the end of that piece of tippet, add your stonefly pattern.

Cast this rig as close to the bank as possible. Use a walking mend when necessary to get into feeding lanes. From a drift boat, it is much easier to swing flies into banks and under bushes. This is done at the end of long drifts, by gradually raising the rod tip and keeping the point fly out of the bushes while your longer dropper is swung into cut banks and under overhanging shrubs. This can be done wade fishing too, but the whole process happens much faster. Wading the swing is going to occur at the end of the drift.

When should I Fish Dry Fly Patterns for Stonefly Hatches?

When stoneflies are hatching, fish can be looking up any point of the day. I prefer to fish an indicator rig early in the morning. Typically, if fish are looking up, a few will come and either look at the indicator, or straight up eat it. This is your clue to switch patterns. This an optimal time to switch to a dry dropper rig, like the one I outlined above.

Once you switch to a dry dropper setup, it will be evident if made the right choice. The dropper will usually get double the eats the large foam dry fly will. If this is the case, then the choice to stick with that rig is up to you. Many anglers prefer to fish a single piece of foam and catch less fish, but only catch them on top. I’ll take eats over tradition any day of the week.

There are times during stonefly hatches that the top water bite is so hot that the dropper is in the way. In my experience, there are two reasons for this: First, the fish are so keyed into to the adults on the water’s surface that they ignore the dropper, or the dropper is being fished below trout that are holding in the very top of the water column. Secondly, the dropper is not allowing the angler to present the fly close enough to bank. Therefore, your pair of flies, although close to the bank, are outside of the fishes feeding lane. Cutting the dropper off solves this problem, and allows cast as tight as possible to stream side bushes.

One of the most fun aspects of fishing a stonefly hatch, is that many species will run across the surface of streams and rivers. A dead drift presentation will work well, but lifting your rod tip and periodically twitching or skating your foam dry fly can elicit massive strikes. Fish key in on flies that create small wakes and push water.

The female stone fly must return to the river, land and deposit her eggs. Unlike, grasshoppers, many species of stoneflies will run back across the water in an effort to return to the safety of the bank. This is a major moment of vulnerability, and one anglers should try to imitate and take advantage of. Fish look for the surface disturbance as an indication that there is a large meal franticly trying to get out of the river.

Are Stonefly Hatches Overrated?

When planning a trip around fishing a stonefly hatch, odds are that you are going to be very disappointed. Stoneflies are sensitive to environmental conditions, and it is impossible to know when the peak of any hatch is going to happen. Furthermore, stoneflies are a large meal, and this can actually cause fish to stop eating all together.

I have fished rivers covered in salmon flies, with no fish eating. This will leave most anglers scratching their heads and frustrated (including your guide). Below is a brief descriptions of my experience with how some of these hatches have played out on my home river the South Fork of the Snake. I fished it for ten years, and almost every time it unfolded in similar ways. Also, below is assuming you are on the right section of the river, as the hatch moves up river. Some sections will produce better angling then others.

Pre Hatch: no bugs on the water – nymph fishing is usually great leading up to hatch

Start of the Hatch: the presence of nymphal shucks and few adults can be found in the bushes and on the water. Dry fly fishing is not good, but fishing nymphs under an indicator is still great.

Full Hatch: All types of fishing is really good, and fishing single pieces of foam tight to the bank can be incredible. Swinging nymphs under a dry dropper is great too. This last 2-3 days. Fishes stomachs will be engorged, looking like they are about to pop.

Just after the full hatch, there will still be many bugs in the bushes and water, but for 2-5 days the fishing will be terrible. This is most likely that fish are full and will stop eating. They need to metabolize the incredible amount of calories consumed.

Post Hatch: Most larger stoneflies like salmonflies will be gone, but other species are still present. Medium sized golden stones and small yellow sallies will stay for most the summer, offering fish plenty of food other then caddis or mayflies. The fishing will pick and fish will still look at adults on the surface.

Different Types of Stoneflies Important to Fisherman

All the stoneflies that are discussed below are important to fly fisherman. While there are many species in the world these are the ones that count for most anglers. For the most part they all follow the same hatching process. Fly selection is rather similar as well. There are some differences in behavior, appearance, and the times of year that they hatch.

Hatch: Skwala Stoneflies

Size: 35mm – 25 mm

Color: Olive to Black

Nymphs: Pat’s Rubber leg, Donkey Stone Dark, Tungsten Girdle Bug Jig, Hares Ear (Sizes #8-#12)

Dries: G’s Superfly (Colored Black or Olive), Chubby Chernobyl, Water Walker (Sizes #8-#12)

Season: Late February, March, April, and May depending on the river

The Skwala hatch is the earliest big bug hatch of the season. This is a pre runoff hatch, and it depends on where you are fishing, but most of the time the conditions will be cold. The optimal water temp for a Skwala hatch is 43 degrees. In many places snowfall will still be on the ground and flurries will still be occurring. Nonetheless, lethargic trout become very active and eat foam bugs on the surface, and nymphs subsurface.

Hatch: Salmon Flies

Size: up to 3 inches

Color: Orange and Brown or Orange and Greyish Brown

Nymphs: Pat’s Rubber leg, Donkey Stone Dark, Tungsten Girdle Bug Jig (Sizes #2-#6)

Dries: G’s Superfly, Chubby Chernobyl, Bank Robber, Stimulator in Orange, Water Walker (Sizes #2-#6)

Season: Mid May to Early June

These are the largest variety of stone flies that anglers will encounter during the fishing season. They are enormous. They also have accents of bright orange, which makes them unique and highly visible. Salmon flies prefer grassy banks.

Not all banks fish the same, so finding areas where salmon flies are hatching in abundance is key. If you are in a boat, keep moving and cover more water to find banks. If you are wade fishing, walk and keep walking. As a general rule of thumb on public water, the fishing usually gets better the further you walk from the parking lot. The tactics discussed prior will work for this hatch.

Hatch: Golden Stones

Size: 35mm – 25 mm

Color: Yellow, Brown, and Tan

Nymphs: Pat’s Rubber leg, Donkey Stone Dark, Tungsten Girdle Bug Jig, Hares Ear (Sizes #8-#12)

Dries: G’s Superfly, Chubby Chernobyl, Bank Robber, Stimulator In Yellow, Water Walker, Circus Peanut (Sizes #8-#12)

Season: June to July and sometimes into August depending on the river

While Golden Stones can hatch the same time as salmon flies, They usually start to appear late in the salmon fly hatch, and will continue through much of the summer. Although they are less in number then salmon flies, the hatch can continue through out most of the hot summer months. They play an important roll in food source availability to eager trout looking to bulk up through the summer.

In my experience, The fishing will be hot during the salmon hatch. When that concludes, the fishing will die for a week as a trout’s diet requires them to metabolize the incredible amount of food they have eaten over the salmon fly hatch. Golden stones will still be around and because of the recently completed salmonfly hatch and other hatches starting to develop, fish will still be looking up. This can provide some of the most consistent and longest dry fly foam fishing of the year.

Hatch: Yellow Sallies

Size: 12mm – 6mm

Color: Yellow, Brown, even Fluorescent Green

Nymphs: Pheasant Tails, Hares Ear, CDC Jig Head Pheasant Tails (Sizes #12 – #16)

Dries: Head Light Yellow Sally, Eric’s Yellow Sally Stonefly, Yellow Stimulator (Sizes #12 – #16)

Season: All Summer

Yellow sallies appear very similar to golden stones. The main difference is they are very small. I have seen them in many different shades of yellow as well. I have even encountered a yellow sally hatch on the south fork that appeared almost fluorescent green in color. They are important to a trout’s diet because they are typically present in large numbers. The females will have a small red egg sack on the end of their abdomens. This plays a role in many fly patterns.

I prefer to fish sally imitations on a tandem dry fly rig. In my experience, during the months of July and August, sallies will be hatching when other similar sized mayflies and caddis are hatching. I have the best luck fishing sally fly patterns over gravel bars with rising fish actively eating dry flies. Often times, when they start to refuse mayfly or caddis fly patterns, presenting a yellow sally will result in fish caught.

In addition, when sallies are present, the nymphs are eaten in great numbers. This is the perfect opportunity to prospect with a dry dropper pattern. There are so many different species of bugs on the water that choosing an impressionistic fly pattern like a hares ear or cdc pheasant tail will cover many different hatches with a single fly. This an excellent mid day tactic for covering many hatches at once if you are having a hard time discerning which bug the fish are on.

Hatch: Mutant Stone

Size: up to 30mm

Color: Brown, Grayish/Olive

Nymphs: Rubber Legs in Orange and Black (Sizes #6 -#8)

Dries: September Stone Water Walker, Chubby Chernobyl, Casey’s Creature, Brenda’s Plan B (Sizes #6-#8)

Season: End of August and September

Mutant, or wingless stoneflies, are a rarity in most places. They are present in streams on the West coast and specifically in the Yellowstone region. These stoneflies are very similar in appearance to golden stones in size and shape. What sets them apart is there hatching behavior and anatomy.

For starters, mutant stones hatch in the fall. This is the latest stonefly that most anglers will encounter during the fishing season. By this time of the year, the strongest hatches have dissipated and the only food source on the water is October caddis and midges. This makes them a very desirable late season meal for trout.

In addition, unlike other stonefly species that hatch during the day time. Mutant Stones hatch at night. Some of the best fishing of the year can take place on a full moon at midnight or 1 A.M. in the morning. When I guided at Worldcast Anglers, we would sometimes fish at our overnight fishing camp on the South Fork of the Snake. Nothing is more exhilarating then putting clients to bed, firing up the jet boat, and skating foam flies under the light of a full moon. The best fishing during this hatch is at night or in low light conditions very early in the morning to about 10 am.

Lastly, mutants are distinguished by their failure to develop a full set of wings. They have short stubby wings that make them terrible fliers. They spend the majority of their time running across the water’s surface. For anglers, an active presentation of skating flies is the best way to fish foam patterns for a mutant hatch. Huge blow ups and fish chasing surface flies is a fun way to fish.