Baitfish, crustaceans (freshwater shrimp or scuds, sowbugs, and crayfish), terrestrial mammals, and uncategorizable food sources such as eggs and worms all can be important food items. While not as ever-present as aquatic insects, most prey items that fall into the categories I just mentioned are not to be dismissed. In many situations, they will actually be more important than insects. The only reason each of the above categories don't deserve their own pages is because a relatively small number of patterns and tactics will cover each, even when they're important.
Note that there's a lot of overlap between patterns in this "catch-all" category. Woolly Buggers can serve as baitfish patterns, leeches, or crayfish, for example. In addition, many patterns on this page qualify as attractors as well as imitative patterns. Is a fish eating a San Juan Worm as a real worm or just as a gob of something edible floating in the water? You catch my drift. In general, if a fly looks like some kind of real food item, I discuss it on this page. If it instead looks generally edible, provided I have not discussed it on one of the other pages in the Flies & Hatches menu, I discuss it on the Attractors page. If you can't find something, contact me using the links and the bottom of the page.
The following "other stuff" can be important, depending on season, body of water, and your goals. The following list presents them in approximate order of general importance. As always, check the relevant page in the Guide to Area Waters section for more details:
The following table covers important non-insect trout food in the region in the region, from most important to least. Note that this is a general chart. Crucial prey items on one body of water might be rare or even absent in others. Check the appropriate page under the Guide to Area Waters menu above for charts specific to all area waters.
If you wish to print a full-size version of this chart, those covering insects important when fly fishing the Yellowstone area, and all other charts on this site, please visit this link.
Baitfish or at least smaller trout are present in all area waters, big and small, and they are preyed upon by trout larger than about 10 inches at least from time to time. On larger rivers with the exception of the Missouri, trout over about 16 or 18 inches will feed primarily on fish. As such, baitfish imitations are your best choice of patterns overall if your goal is to catch trophy trout. There are a few times and places this is less true: during spawning runs when nymphs and eggs work just as well, on tailwaters when even very large fish can find enough insects and crustaceans to eat, on lakes where leeches and worm imitations are more common food sources for big fish, and during Salmonfly hatches. Otherwise, if you want a pig, throw a streamer.
That said, streamers are usually not the ticket for numbers of trout. Until trout get to 14-16 inches, or even larger on tailwaters and lakes, they primarily eat insects. When you throw a baitfish imitation instead, you are cutting off probably the bottom 2/3 or 3/4 of the population. Small and average trout are just as likely to be spooked by a baitfish imitation as eat it, particularly if you're using one of the huge contemporary articulated patterns. The one major exception to this rule is hike-in portions of the Yellowstone in it canyons in Yellowstone Park, where huge numbers of trout are sometimes willing to chase and eat small and medium-sized streamers.
Good streamers can be divided into several classes. They are presented and discussed in the following list in order of general usefulness:
Note that there is a great deal of overlap between streamers and leeches, particularly since Woolly Buggers are good imitations of both fish and leeches (as well as crayfish). There is also some overlap between large wet flies and streamers, particularly steelhead-type wet flies that can interest fall-run browns. These are discussed on the Attractors page.
Scuds are vitally important on tailwaters and are also good choices on spring creeks and lakes. On tailwaters, they're mostly a late fall through runoff pattern, while on lakes and tailwaters the trout might eat scuds on an opportunistic basis at any time. There's some difficulty in identifying scuds vs sowbugs. They're about the same size and livev in the same water. In general, a real sowbug or a fly imitating one will be broad and flat. A real or fake scud will be narrow, with a fuzz of legs or fly tying materials imitating legs projecting from the bottom. Both have notable shells over their backs.
On lakes and spring creeks, fish naturally-colored scud patterns. The best overall color is grayish olive, while tan and dark olive can also work. I prefer ostrich-herl bodied patterns like Minch's Herl Shrimp***, but standard fur-bodied scuds are also good choices. On lakes, fish scuds with a slow retrieve along weed beds, while in spring creeks dead drift them. Patterns in #12 to #18 work on lakes and spring creeks, with the smaller flies generally better.
On tailwaters, the natural colors mentioned above can work, but scuds are also effective in pink, orange, and rainbow (a specific shade of sow-scud dubbing offered by multiple manufacturers). These patterns may be tied with ostrich herl or with dubbing, and often include hot orange "firebeads," pearl or silver flash, brightly-colored ribbing, and other features that make them more visible and ostentatious to the trout. By this same token, larger scuds can be effective in tailwaters, particularly in late spring when the water is up, with #10 to #18 flies all good choices, and #10-14 often best in late April and May.
Besides generic scud patterns, of which there are vast numbers, all of which work, a very popular category of flies on tailwaters in particular are Czech Nymphs in pink or rainbow colorations, of which the AMEX and Rainbow Czech are the most popular examples. These patterns look somewhat like scuds, somewhat like sowbugs, somewhat like eggs, and somewhat like caddis larvae or pupae. As such, they are excellent choices when the trout are feeding opportunistically. They are most popular and effective from late November through mid-May and are most-often used as top flies with a smaller egg or nymph dropper. Both standard and firebead versions work well, generally in #12 to #16.
Egg patterns are vitally important in late winter, early spring, and from early to late fall, but only where spawning or pre-spawn fish are present. These include rainbow trout from February through May, browns from September through December, suckers in late May and early June, and whitefish in September and October. Of these the rainbow and brown trout are most important. While it is not sporting to fish for actively spawning trout, plenty of their cousins of whatever species eat eggs these fish release, both during the spawn and simply when a few early eggs dribble out as the fish prepare to spawn. It is also acceptable to fish for pre-spawn trout. Look for both non-spawning fish and pre-spawn fish in the deep runs and pools downstream from spawning areas. Except during peak spawn, eggs should be fished in conjunction with another nymph that is heavier. In fact, it's usually better to show the fish something different in addition to an egg.
Egg patterns should be #16 and in colors including pale pink, dark pink, pale orange (apricot), and even chartreuse. The best colors depend on lighting conditions and water clarity and I suggest carrying all of the above. Good patterns include basic Glo Balls, which are your standard egg patterns, Y2K Eggs, and Alaska-style 6mm Egg Beads. The latter are of at best questionable legality in Yellowstone Park but are legal in Montana.
The rivers where eggs work best are the Missouri between Hauser Dam and Holter Reservoir, the Gardner, lower Firehole, lower Gibbon, Madison between Hebgen and Quake Lakes, and for brief periods the Yellowstone. On larger rivers, don't bother fishing eggs except near large tributary creeks in late winter and spring and downstream of good spawning water in late October and early November. The major exception to this rule is the section of the Missouri previously noted, where eggs work everywhere due to a major rainbow spawning run from Holter Reservoir.
Note that the assorted pink mayfly nymphs, scuds, sowbugs, and Czech nymphs that work very well in late winter in spring, as well as any pattern featuring an orange firebead probably trigger an "egg response" in the trout. I believe such patterns look enough like eggs and other food items that they can offer the best of both worlds: they catch both egg-eaters and trout interested in more conventional foods.
Sowbugs are most important on area tailwaters, though they are also present in spring creeks and to a lesser extent in lakes. While they can be important all year, they are particularly good from late autumn, through the winter, and through the spring runoff cycle. In the dead of winter, pink or rainbow patterns, often with "firebead" heads are among the best flies you can fish on the Missouri overall, when they imitate both eggs and dead/dying/pregnant sowbugs. By mid-May, rainbow or gray-colored patterns lacking firebeads are usually better. Always fish sowbugs on a dead drift. Good sowbug-specific patterns include Soft Hackle Sowbugs, Soft Hackle Firebead Ray Charles, Tailwater Sowbugs, Killer Bugs, and Poxyback Sowbugs. The multi-purpose Czech Nymphs mentioned in the scud entry are also good choices. Pattern size should range from #12 to #18, with the largest patterns most likely to work best during runoff when even the Missouri gets high and fast, with smaller patterns best in lower water.
Worm imitations, whether these look like aquatic worms or terrestrial worms that have washed into the water after rains or during runoff, are good choices in most locations at least part of the year. Overall they are most important on tailwaters. On the Missouri in particular, they work well from late fall through at least the middle of June, with their highest productivity during the high water of spring. At this time, very large, heavy worms are good, while in winter smaller, sparser flies are better choices. Good colors are red, wine, pink, and brown, or combinations of these. Good patterns are beadhead and other weighted San Juan Worms from size-8 to size-16, while during the high water of spring, extremely large Wire Worms with or without firebeads in the middle are good. These can be tied on hooks as large as #4, with #6 to #8 standard.
On spring creeks, worms are good in the winter and early spring. The colors mentioned above are good choices. Use smaller beadhead or plain San Juan Worms in about #16, or the even skinnier Floss Worm.
On weedy lakes, especially private lakes, worms are good choices in the spring and to a lesser extent in the fall, particularly when the lakes are somewhat off-color. Similar patterns as noted for tailwaters are good on the lakes, with the larger patterns best when the water is colder and/or dirtier. Dark reds, purples, wines, and browns are usually better color choices than pink on the lakes, probably because worms in these darker colors also double as leeches.
On freestone streams and rivers, worm patterns are much less effective. They can work in large sizes at the tail end of runoff or during and just after sudden storms, as the water is starting to come up and get dirty. Some anglers also like them for fall-run browns (I do not). Otherwise, their utility is limited to the occasional fish that will take a worm as an attractor, which happens from time to time on heavily-pressured water like the Lamar Drainage.
Leeches (often just small, sparse Woolly Buggers) are very good choices on weedy, shallow lakes. This is particularly true immediately after ice-out in the spring through May, then again after water temperatures start to plummet and the weeds start to die back by late September. In both cases, leeches provide a lot of calories for fish that are either recovering after a hard winter or trying to prepare for it. Fish them either twitched under an indicator or on a full-sinking line. The fish generally like them retrieved slow. Good patterns include standard Simi-Seal Leeches, Goat Leeches, Pig Pen Leeches*** (a sparse multi-colored bunny and marabou leech), and small (#10 to #14), sparsely tied Woolly Buggers. Pig Pen Leeches are good in #4 or #6, while the others are better in #10 to #14. Good colors include the following, often in combination: black, red, burnt orange, chocolate brown, golden brown, and both light and dark olive.
Crayfish are unimportant in the Yellowstone area for one simple reason: they are found only in low-elevation locations. These include the Madison River below Ennis Lake, the Missouri River, and the Yellowstone River east of Livingston. There are also a few in assorted lakes at low elevations, particularly private lakes. There are no crayfish at all (or so few as to amount to the same thing) in any fishery of note in Yellowstone Park, the upper Madison, any small stream outside the park, the Gallatin, or any spring creek. The only place where dedicated crayfish are routinely effective is the Lower Madison, though some "junk bug streamers" like the Zirdle suggest crayfish as well as other food sources and work well on the Missouri and Yellowstone downstream of Livingston. On the Madison, make sure to carry Clouser Crayfish and more impressionistic patterns including the aforementioned Zirdle and brown Woolly Buggers to match crayfish. Unless you're hunting one big brown, fish smaller (#6 to #12) crayfish patterns under indicators alongside a nymph of some kind. If you are hunting big browns, fish much larger flies, including bass patterns or articulated streamers in combinations of tan, brown, rust, and olive. You might only get one or two strikes a day doing this, but the fish in question might be the biggest one you ever see.
Crayfish patterns are most effective from May through September. They are not good choices in the dead of winter as these critters hibernate in burrows when the water is bitter cold.
Here's an oddity: there are crayfish in one place in Yellowstone, the appropriately-named Crawfish Creek, a tributary of the Lewis River. How they got there is anybody's guess, but they've been there long enough for the creek to earn the name. A few cutthroats from the Lewis spawn in this creek in May and early June, but it's a geothermal stream that gets far too warm in midsummer to host a fishable number of trout. It's the hot water that makes the creek hospitable to crayfish.
The Yellowstone area isn't Alaska, so mice don't produce numbers of trout here. That is not to say they produce none. For whatever reason, big trout are fascinated by mice, or at least mouse imitations, and if you put in the time and effort to fish mice near dusk on any big fish fishery, or even after dark under a full moon where doing so is legal, you will be rewarded by a handful of extremely aggressive strikes from very large fish. Good places for this tactic include fertile lakes known to produce trout over 18 inches, the Yellowstone River in Paradise Valley, the Missouri, the Lower Madison, the Paradise Valley spring creeks, and lower Slough Creek. You will not catch a fish every time you do this, no matter how good an angler you are, so this is only for anglers who want the thrill of a very occasional strike like a toilet flushing under your fly. Skip the fancy deer hair mice. Instead use patterns constructed of rabbit fur and foam, even the dirt-simple and largely forgotten LaFontaine's Creature. Mice should not be enormous, say about a size-4 (though this is still a big fly). Fish them on tippet no lighter than 2X, and you can get away with tippet so heavy you can barely pass it through the eye of the fly. Midsummer is the best time to try this.
It is not impossible but is highly unlikely that you will ever need to match birds, amphibians, lizards, snakes, or anything else. I'm not saying trout don't eat these creatures, because they certainly do, but they are likely to do so only in a purely opportunistic manner. As such, a fish that is looking for tadpoles will probably eat an olive Woolly Bugger. A fish that would take a shot at a baby bird that falls from its nest would probably eat a big grasshopper pattern or a mouse. If you have bass flies resembling any of the above, go ahead and try them. I'd be very curious to know how you do.
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.
All text copyright Walter J. Wiese. Photos copyright Walter J. Wiese or the photographer. If you would like to use any of the content on this site for noncommercial purposes, you are welcome to do so provided you include this copyright notice and our contact information. Please do not use the information here for commercial purposes without written permission.
Website, text, and graphics by Walter J. Wiese. Photos generally by Walter J. Wiese unless noted.