This page and the other pages in the Flies & Hatches dropdown menu are designed to give a thorough rundown about when and where to expect certain insects to hatch and draw the interest of trout, when and where certain flies and types of flies can be expected to prove effective, and how to fish these flies in the Yellowstone area. This page gives a very general overview and a list of forty fly patterns that will get you at least some fish just about anywhere in the region, year-round. The other pages go into much greater detail.
The flies in the following four lists should produce at least some fish regardless of when in the year you come to the region. I want to be clear that not all will work at any one time or even on any single water. Fishing egg patterns, Soft Hackle Sow Bugs, and pink Lighting Bugs on the Yellowstone at the tail end of the spring melt will be worthless, while brown Girdle Bugs and Bitch Creeks might put you on so many fish your arm will be tired. Fish the Missouri River in March and the opposite will be true, for example. Once you get a sense of when you might be coming, check the Seasons page and the pages within the Guide to Area Waters section of the site to begin narrowing the list down quite a lot. You might be able to get away with three or four of the following flies, plus three or four more-specialized patterns, on any given body of water at any given time of year.
Many of the patterns in the following lists are marked with three asterisks (***). These are all Yellowstone area or Montana trout flies developed by fly shops or fly tiers specifically for this region. Some are my own patterns. Many are by other tiers. I suggest Googling the patterns to find out more, in particular where you might purchase them or learn how to tie them. Patterns without asterisks should be more generally available, even if they are unfamiliar to you.
The following dry flies include imitations of the most common area hatches and some crucial terrestrial and attractor dries.
The following patterns include basically any sort of pattern that is designed to be fished primarily on a drag-free drift near the bottom, including mayfly and stonefly nymphs, caddis and midge larvae/pupae, eggs, scuds and sowbugs, and worm imitations.
The following patterns approximately cover all flies that are designed to be fished with an active retrieve to imitate all sorts of baitfish, leeches, and the occasional crayfish.
The following patterns are designed to be fished primarily near the surface either in tandem with another wet fly on a traditional swing or as a dropper under a dry fly. All match emerging or egg-laying insects of one type or another. Included here are caddis pupae designed to be fished shallow. Those designed to be fished deep are considered under the "nymphs" heading.
Mayflies, Caddisflies, Stoneflies, Midges, Baitfish, assorted acquatic crustaceans, eggs, terrestrial insects that fall in the water, and various other "stuff" can all interest our trout at certain times of year and in certain places. In a lot of others, generic patterns that look sort of like a whole bunch of things are more important than flies that look like anything in particular.
Mayflies are found on all area streams and lakes. That said, they need to be matched with precision on a far smaller set of waters. It is typically unimportant to match these insects specifically on small and especially rough mountain streams, where attractor dries do just fine. They are also of only spotty importance on large, rough rivers like the Yellowstone. In the summer months, big, brawling water like this will only see the fish keying on mayflies in isolated areas. In the spring and fall when waters are slower, the fish will key on Blue-winged Olive and some other mayflies much more thoroughly on rough waters. Mayflies are of much greater importance on flatter meadow-type streams and rivers as well as spring creeks and tailwaters, where for most of the season matching hatches of assorted mayflies is the best option for good dry fly fishing. They are of lesser importance on lakes, but when mayflies do hatch on lakes, again the dry fly fishing can be much better than it usually is on such waters. Mayfly nymphs and attractor nymphs that push the "mayfly button" are good general searching patterns, particularly on tailwaters, spring creeks, and meadow-type streams. Check the Mayflies page for much greater detail on specific hatches.
Caddisflies are our most widespread summer insects and hatch from all waters, especially all flowing waters big and small. Some waters, particularly the Yellowstone and Madison, also see important hatches in early May, before the heavy runoff hits. That said, caddis usually need not be matched with any precision. Instead, fish attractor dry flies and nymphs in approximately the right shape and size. This is because caddis typically hatch in low numbers through the afternoon through most of the summer, and are generally "active," flitting this way and that and thus leaving the trout little time to inspect them before eating. You need plan to get more exact only on larger and/or flatter streams, including all "big name" fisheries, where heavier hatches occur, particularly in late June and July. You almost never need to match caddis hatches precisely on small streams or even on the roughest portions of large streams. Higher-floating attractor dries are better bets on these waters even if you see caddis flying. Caddis hatches can occur at any time of day, but are most common in afternoon and evening except on the Firehole River, where they often occur in the morning. Wet flies and nymph patterns imitating (at least roughly) caddis larvae and pupae are very good general searching patterns and often work well when fished just under the surface during hatches, as well. Check the Caddisflies page for more details.
Only a few species of stoneflies are important, and they are only important on a small number of waters for a small amount of time, usually just as the spring runoff recedes and perhaps for a few weeks afterwards. Small and large freestone rivers with fast, turbulent flows and a bottom comprised primarily of fist-sized and larger rocks and boulders make the best habitat for all species of stoneflies, particularly the marquee Salmonflies and Golden Stoneflies, which are the largest aquatic insects in the area and the most likely insects to interest even large trout. Tailwaters with the exception of the Madison, spring creeks, and lakes do not hold fishable numbers of stoneflies. Meadow-type freestone streams and rivers as well as small streams of any character usually hold only scattered populations of small stoneflies which are seldom important to the trout. On big, fast-flowing rivers, stonefly nymphs can be great choices at any time, particularly near the summer emergence and when brown trout and rainbow trout are running. See the Stoneflies Page for more details.
Midges are most important on tailwaters and spring creeks throughout the year, faster-flowing freestone rivers during the winter, and occasionally on meadow-type streams like the Lamar in the fall. Larger "chironomid" midges are critical on lakes, especially in early summer. Except for the chironomids, midges are all small, typically #18 on down to #24. They can be important on the surface when winds are calm, but larvae and pupae fished as nymphs are far more consistent overall. During the winter, midge imitations as well as attractor nymphs that look more or less like midge larvae or pupae are likely to be your most important flies overall at least until the rainbows begin running in late winter. Check out the Other Insects Page for more details on midges, as well as less-important aquatic insects.
Baitfish are prime food for larger fish (any trout over about 14 inches) on all rivers. The smaller the stream in question and the smaller the average trout in it, the less important they are. They are also somewhat less important on tailwaters than other flowing water, because tailwaters produce so many insects and crustaceans that larger fish do not need to switch from these smaller food items to other fish at as small a size. Even taking that fact into consideration, you can expect that the largest river-dwelling trout you will see in a given season will almost always eat some kind of baitfish imitation. Except on the hike-in portions of the Yellowstone River inside Yellowstone Park, they are seldom your top bet for numbers of trout. On larger natural lakes as well as the large reservoirs in the area, baitfish patterns may be your best bets overall for both numbers of fish and size of fish. The smaller, shallower, and weedier the lakes, the less important baitfish will be. Yellowstone-area trout are not picky in terms of baitfish imitations: as long as you have some kind of #4 to #6 Woolly Buggers, sculpins, and a flashy pattern such as a Kreelex or two, you will be able to catch some fish. Large contemporary articulated patterns are not legal in Yellowstone Park and otherwise are only important on large rivers. Don't hesitate to double up on streamers. Fish a little one as a dropper "second chance fly" between a larger and more ostentations fly.
Aquatic crustaceans, basically meaning scuds (freshwater shrimp) and sowbugs, are most important in shallow, weedy lakes, spring creeks, and tailwaters. They are generally unimportant in freestone rivers and all smaller streams with the exception of spring creeks. On tailwaters, they are often the best flies in late winter and early spring, both because these critters are one of the few fairly large food sources at this time and because many sowbug and scud patterns can double as eggs. Crayfish, the most important crustacean in many other parts of the world, are not very important for fly fishing the Yellowstone area. They are not found much above about 4500 feet in elevation this far north, which limits their range to the Lower Madison River below Ennis Lake, the Yellowstone River east of Livingston (and especially Big Timber), and the Missouri River. They are also found in low-elevation lakes on or near these rivers. They fill much the same niche as baitfish in these few waters where they are found.
Eggs of rainbow and brown trout are critically important in late winter and early spring (rainbow) and from September through November (brown). In early autumn, the eggs of whitefish are also important. It's often hard to tell if trout are feeding on early brown trout eggs or whitefish eggs at this time, and it doesn't really matter. Whenever eggs are present, it is common for trout to feed voraciously on them. They offer good nutrition and won't escape like prey species. Fish eggs in deeper water downstream of shallow spawning areas in any stream that hosts spawning runs, big or small, as well as in larger rivers immediately downstream of spawning tributaries. You can also try fishing eggs on windswept banks and near stocking areas in lakes, as the stocked trout in these bodies of water will move to such locations to attempt to spawn if they can't enter tributaries. Good egg patterns range from cream to pink to orange to chartreuse in color, and should be about #14 to #16. Note that soft plastic or rubber eggs are not legal in Yellowstone Park.
More information on baitfish, aquatic crustaceans, and eggs is included on the Other Trout Food page.
Terrestrial insects including grasshoppers, crickets, cicadas, ants, beetles, spruce budworm moths, and bees are vital parts of the angler's arsenal from July through September. Of these, the largest hoppers, crickets, and cicadas are most popular with anglers and are more likely to produce big trout, but the smaller bugs, particularly ants, are most likely to produce big numbers of fish. Spruce moths are important only near evergreen trees, though there don't need to be too many evergreens for these insects to be common. All terrestrial insects are most important on freestone streams of any size, from tiny mountain creeks on up to large rivers like the Yellowstone. Quite often, they will outperform aquatic insect imitations on waters of this type in August and early September, particularly during bright, hot weather. They are less important on tailwater rivers, spring creeks, and lakes, but they can be important even on these waters. Beetles and ants in particular can work anywhere that a hard wind might be expected to blow a few insects from bankside vegetation into the water. Learn more on the Terrestrials page.
Other food items that sometimes interest trout include leeches, worms (aquatic and terrestrial), damselflies and dragonflies, water striders, birds, mice, and basically anything trout can fit in their mouths. Worms are the most important of these. San Juan and similar worm flies from huge to tiny can be very good at any time on shallow, weedy lakes and on tailwater rivers, while tiny versions are good searching flies on spring creeks. They can also be good on freestone rivers and streams when the water is on its way up after rain showers and at the tail end of runoff. Mouse patterns can draw one or two explosive rises per day, from very large fish, but they are never consistent choices. They work best when fished when the light is off the water, even at night (where legal). Otherwise, all of the flies in this "none of the above" category work best on lakes, though small leech patterns often substitute as baitfish and vice versa (i.e. small Woolly Buggers). Learn more on the Other Trout Food page.
Generic attractor flies, both dry flies and nymphs, as well as the most-common streamer flies such as assorted Woolly Buggers, are often much more effective than imitations of specific insects. This is particularly true on rougher streams and rivers, regardless of size. In general, trout are more likely to take attractors when the water is somewhat high and when numerous types of insects are available, for example in July on the Yellowstone, Gallatin, and other rough rivers and streams. They are also to prefer such flies (or terrestrial insect imitations) on all small streams except spring creeks. They are less likely to want such flies during heavy hatches of one particular insect, in slow water, and on spring creeks and tailwaters, which typically have fewer types of prey but much higher individual numbers of each type. Most of the beloved "classic" and "Western" patterns fall into the category of attractors: Stimulators, Wulffs, Trudes, Chubby Chernobyls, Prince Nymphs and many other generic nymph patterns are prime examples. Even when insect hatches are underway, attractors in the right size can work better. Trudes or my similar but lower-floating Clacka Caddis work great during caddis hatches, Stimulators work great when stoneflies are hatching, and Wulffs and the newer Purple Haze Parachute and my Purple Hazy Cripple are regional favorites when mayflies are hatching. Many of the patterns I present in the "Top Forty" at the top of this page fall into this category. See the Attractors page for more details.
Walter Wiese is Montana Outfitter #22001 (formerly guide #9530) and Madison River SRP Holder #297. Yellowstone Park trips are run in cooperation with and under the permit of YNP CUA holder Richard Parks.
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Website, text, and graphics by Walter J. Wiese. Photos generally by Walter J. Wiese unless noted.