Big Bugs on the Henry’s Fork

You brush off the insect that was skittering above your shirt collar, and then adjust your shades. A sundown of twisted gold and pink is mottled in the broken evening clouds, reflected back up to you from the swirling currents of a spring creek in Harriman State Park. Sitting behind the grass sprouting up from the river’s edge and watching the mayflies dance up and down in swarms, your hands collect up the slack line and prepare your cast. Your target, the rising ‘bow who has been steadily breaking the surface in front of you.

The extended body mayfly zips through the air with each false cast, until its uncommonly large silhouette dimples softly onto the river. As the other large mayflies begin their flight from the water’s surface, an image of tiny sailboats drifting out to sea unfolds before you. Before long, you’ve lost your fly in the mix of bugs. You could’ve sworn you just had it...

The ring of the rise pushes the water so suddenly, you set the hook instinctively. The movement cascades mist into the evening air, carried by the fly line you zip from the calm surface. And then, with a heartstopping tug, the line pulls back.

Fishing big dries is hard to beat. They float well, are easy to see, and big trout prefer a larger meal. Feeding a big railroad-ranch rainbow a brown drake imitation, or a kyped-up brown a big hopper downstream is a killer plan for a fishing trip. But how do you know when these hatches happen if you are new to the river?

The Henry’s Fork of the Snake River provides great opportunities for fishing all summer and well into autumn. If you’re someone looking for their first dry-fly experience on the Henry’s fork, you should really try to come fish the river during one of its famous hatches. It is a dry-fly fisherman’s paradise. This is a short beginners guide to some of the Henry’s fork’s larger bugs. Hopefully it helps you plan your next fishing trip to float some big flies.

Substantial Stoneflies

Stoneflies are numerous in the Henry’s Fork, and a good year for stoneflies makes for some of the most exciting fishing of the year. Whether slinging big foam flies from a drift-boat or on foot, stoneflies are a hatch every flyfisherman on the Henry’s Fork spends all winter daydreaming of.

Stoneflies in general tend to prefer faster, more oxygenated stretches of the river. As the hatch begins, the nymphs crawl their way to the banks, shed their outer layer and then emerge as adults. Keep your eyes open in Box canyon around May, looking for fresh stonefly shucks, they’ll let you know if the bite is on. The two big bruisers of the stonefly world are the Salmonfly and the Golden Stone.

Salmonfly, Photo by J. Huddleston

Fishing the salmonfly hatch is an explosive start to the summer. Not only is it the first predominant large insect emergence of the summer season, it is the largest aquatic insect on the Henry’s Fork. In a typical year, the salmonfly emergence will be from mid May to mid June. Most hatches progress upriver, and the salmonfly hatch is no exception. The adult insect first starts to show up downstream in St. Anthony, and the hatch moves its way upstream in the following days ending in Box canyon. If you find yourself upstream looking for the salmonfly hatch early in the emergence, you can always fish your way downstream until you start to find these big guys.

Salmonflies are available to trout as both nymphs and adults. The immature nymphs are large with pronounced legs and body plates, easily imitated with a black or brown Pats rubberlegs, sizes 6 or 8 fished in fast riffles or underneath a dry early in the hatch. A Henry’s Fork Foam Stone Salmonfly, in a size 4 is a great option for a large dry. Fish it by itself, or hang a rubberlegs or a caddis pupa underneath as a dropper. If fishing under the banks closer to Riverside, or down closer to Ashton, a Flutter bug is a great pattern underneath overhanging trees and around boulders and holding lies.

This is a stonefly as long as a finger, and it will coax up even the largest trout to come eat on the surface. Any angler who has experience with a salmonfly hatch can tell you about the “smash and grab” rises that trout have in response to these insects. It’s the first opportunity most trout have in the season to eat their fill. Don’t miss it! 

Late May to the end of June, the next big aquatic insect joins the menu, and they are a personal favorite to fish. I have fond memories of these clumsy stoneflies climbing over each other on blades of grass along the banks in June, tumbling into the river, and being slurped up by large rainbows in the shallows.

Stay gold, Ponyboy.

Time it right, and you will be in stonefly mecca due to the overlap between the Salmonfly and the Goldens. Anytime early summer, and you will have a great chance of running into this cute little fella streamside. Golden stoneflies have a similar lifecycle to Salmonflies, although their nymphal forms look quite different. These stonefly nymphs range in color variation, much like the adults do, but can be brown or olive with a golden yellow highlight to their appearance. They prefer cold clean water, and prefer to make their habitat in rocky, stony, or gravely riverbottoms; which is why they are aptly named!

If you are looking to target stoneflies, your best bet is to find stretches of highly oxygenated water. Think of stretches with riffles, runs, canyons, anywhere that water turbulence and velocity increases the oxygen content of the water. Box canyon, Riverside campground, and the Warm River confluence all have stretches of water with excellent stonefly habitat.

Mammoth Mayflies

When I first heard the word “drake” as a novice fly angler in a Montana fly shop, a hatch of small dragons emerging from the stream was all I could think of. While not quite as massive as the serpents of legend, the drake hatches of the Henry’s Fork are still just as legendary. Let’s talk about the three main large mayflies, the Green, Brown, and Gray drakes.

A freshly emerged Western Green Drake

The Western Green Drake is usually the first of the three largest mayflies to make their appearance in June, and continuing into early July if conditions are favorable. Because this large mayfly tends to hatch in the afternoon it makes for the perfect angling opportunity, as even the largest fish will be looking to come to the surface to grab a bite.

In addition, it is worth noting that the timing of the drake hatches is usually aligned with the famed “Ranch opener,” which is June 15th. This is the season opener to the famed Railroad Ranch section of the Henry’s Fork, where you will have a great chance to catch a large timid rainbow feeding on the surface in hallowed fly fishing waters.

The Western Green Drake spends a majority of its life as a “crawler” mayfly, preferring faster waters with a gravel or rocky riverbottom (similar to stoneflies). The hatch occurs when the mature nymphs migrate to somewhat slower water, and then rise through the water column to the surface. During this period, they are easy targets for our favorite little slime rockets. Try slowly swinging a large softhackle before the hatch to mimic a clumsy mayfly emerger.

Once reaching the surface, the mayfly has to hatch from its nymphal shuck (like shedding a skin layer) and then dry out its wings before it can fly away, leaving it stranded and vulnerable. Freshly hatched Green drakes are a fascinating bright green color which will quickly fade into a darker brown or reddish color shortly after emerging. This mayfly has three tails, and dark “dun” colored wings.

When I speak to anglers in the shop, they confirm two personal favorite fly patterns work quite well. Lawson’s Extended Body Drake fishes well for the duns, and since these flies are quite clumsy as they emerge and often get trapped in their shucks, a Harrop’s Last Chance Cripple is an excellent choice for more selective fish. Hook size 10 is about right.

The Western Green drake is sometimes confused with a similar mayfly, the Flav. The Flav hatch is a similar mayfly in appearance, but runs a touch smaller in size. The Flav usually hatches later than, and in a sporadic and hard to time emergence, but it is another great insect worthy of note for the Henry’s Fork.

When fishing the Green drake, do not shy away from the weather! The best hatches I have yet to witness all occurred during and immediately following cool summer afternoon rainstorms, and on cloudy humid days. If you find Western Green drakes, it usually means you are in for an epic day on the water.

A Brown drake, Photo by J. Huddleston

After the Greens, then follows the Brown drakes. This mayfly species frequents the slower sections of the river, habitating stretches of streambed where the sand, fine gravel, and silt settles down near the bottom in the reduced current. This is because these mayflies are classified as a burrowing nymph, where they use their large gills to fan water through tubular borrows to breathe.

The adult dun has a yellowish tan belly and a darker brown apex of the abdomen. Three tails and spotted wings is usually an easy way to distinguish this species as well. This is a fun hatch, and evening emergences usually pairs a dun emergence with a spinnerfall. This is when the short-lived adult life cycle of a mayfly is complete, and the “spent” adults fall back to the river’s surface with wings splayed flat following mating.

Be prepared late June and early July on the Henry’s Fork with a collection of both duns and spinner patterns. Lawson’s Extended Body Drake comes tied in the form of a Brown Drake, and Hudgen’s Hackle Spinner is a great option for a spent imitation. The Brown drake is a significant and important hatch on Railroad Ranch, and downstream towards the Wood Road area. There are plenty of access points to fish this hatch, although the river can be quite busy during and immediately following the Ranch opener. I always prefer to walk downstream from Osborne Bridge a ways, or to the footbridge in the state park, and then wander the river looking for risers. Bring a headlamp, you might want to fish until dark for this one!

Freshly Hatched Gray drake, Photo by J. Huddleston

The last of the large drakes is the Grays, which emerges around the same time as the Browns. Most easily identified by the adults having two tails instead of three, the freshly hatched duns tend to have wings darker than the mating adults. Also the longer the mayfly has been out of the shuck, the mayfly tends to lighten up and turn a lighter gray color.

These mayflies also hatch slightly differently than either the Greens or the Browns. Gray drakes are swimmer nymphs, and they tend to inhabit stretches of the Henry’s Fork and frequent stretches of the river with weedbeds and aquatic vegetation, with silty bottoms. Gray drakes tend to migrate to slow shallow scratches of the river and crawl out to hatch, making the duns unavailable to trout unless wind or happenstance happens to knock them back into the river. They do however form large spinnerfalls in the late afternoon or evening time, which is usually how the adults are imitated with an artificial fly.

The Lower Henry’s Fork below Ashton reservoir has excellent Gray drake habitat, where you can feed a big bluecheeked brown trout, a big spent mayfly pattern! Keegan’s Gray Drake is a popular option, and the deer hair wing makes a great profile on the water’s surface. If you can get your hands on some Hudgen’s Hackle spinner, you’re in business. Gray drakes are found also on the Upper Teton River, the Yellowstone River, and nearby Fall River.

Hefty Hulking Hoppers

Mid to late summer, foam flies become king. Rubber legs and sharpied marked eyes on your favorite terrestrials will be the last chance to fish a big dry-fly on the Henry’s Fork. It is also a really enjoyable way to fish, and you will still move large trout on a grasshopper imitation on the Henry’s Fork. Grasshoppers are ectothermic, meaning that their activity level is dependent on the temperature outside. This makes them most active in the middle of the day, but I find early evening is usually the best time to find some luck on a typical August day. August through mid September is typically peak season for hopper fishing, and I find that the large browns on the lower river love a well presented grasshopper tight to the bank.

Terrestrial Season, Photo by J. Huddleston

Our fly shop carries a large selection of terrestrial patterns for the dog days of summer. Lawson’s Henry’s Fork Hopper is a classic by itself, and if you feel tempted to hang a nymph underneath it when fishing slows down, the Thunder Thighs hopper in pink was a solid producer for me last season and has a big yarn wing which floats like a battleship.

If you’re fishing Railroad Ranch mid to late summer, hoppers will work, but always carry some other terrestrial options. A well placed beetle or honey ant may be the trick to fool a spooky rainbow. Mid to late summer is great because you can usually have a stretch of the river all to yourself, and with a little effort you can find some great success.

Fishing a large dry fly is a big draw to the Henry’s Fork, and the unique spring creek characteristics of this beautiful river rears a huge biomass of aquatic insects. May, June, and July are peak times of the year to find yourself in the middle of a flurry of mayflies, stoneflies, and rising trout.

But just because you can’t make it to the Henry’s Fork in May or June doesn’t mean you can’t find large hatching aquatic insects. If dry fly fishing is what you’re after, a nocturnal golden stonefly also hatches in August on the nearby South Fork. Hecuba mayflies, which are similar to a Green drake, make an appearance on rivers in Yellowstone National Park in the late summer where you can fish them to big native cutthroats. Grey drakes start to pop on the Teton in September. Come on into the shop and we’ll point you in the right direction for fishing with big bugs on the surface.

Want to explore more hatches on the Henry’s fork? Click the link above in the banner and get a free hatch guide book, or check out “Bug Hatches” under Fishing Information. If you’re interested in the ecology of aquatic insects, a great website is troutnut.com, if you haven’t checked it out by now, it is a great resource for any fly fisherman.