It may seem counterintuitive, but assorted terrestrial (land-dwelling) insects are vital when fly fishing the Yellowstone area, especially on freestone rivers and streams of all sizes. One these waters, the trout feed aggressively on terrestrials, and they can often produce the most consistent fishing during the late summer timeframe, even to the extent that the trout become somewhat selective towards specific terrestrials just as they do to heavy aquatic insect hatches. More often, the bite is consistent but opportunistic, with the fish eating what's put in front of them provided you cover enough water to find trout that are looking up. In this sense, terrestrials should be considered substitutes for attractor dries. Trout in tailwaters, spring creeks, and lakes don't get quite as excited about these types of insects, but imitations of these bugs can work on waters of these types as well.
Terrestrial insects are only important during the summer and early fall months. All terrestrials can produce from June through early October, with late July through the middle of September the truly prime time. In general, terrestrials are most effective when the early summer hatches have faded somewhat but the fall hatches have not yet begun. More details on timing will be included in the discussion of each individual insect type.
Good terrestrials range from big to small bugs of various sorts. Literally any type of terrestrial bug can interest the trout, from beetles to butterflies. The following insects are most important in terms of numbers of fish they produce throughout the region. I stress this because some insects are more important on some waters than others and some insects produce larger fish than others. As always, check the individual pages within the Guide to Area Waters section of this site for more details on what's important where. The individual bug descriptions below also go into some detail in this regard.
In general, you can expect to use the following types of bugs during the summer months, on one water or another. With most of them, there are several different insect species that fall into the same category, but the trout don't care about the Latin names of the bugs. Instead, I've organized the insects by general type, with one exception, the spruce budworm moth, which is a single species.
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Ants are the bread and butter terrestrials on all major waters within Yellowstone Park except the Yellowstone River in its canyons and the Gardner River. This includes the Lamar Drainage, the Gallatiin, the Bechler System in the park's southwest corner, and even the Firehole, Gibbon, and Madison where terrestrials are not very important. In addition, ants have been my most productive dry flies on the Yellowstone River outside Yellowstone Park in August every season since 2012.
In other words, you need ants in late summer.
Four basic categories of ants are important: high-floating #12 to #16 flying ants, low-floating non-flying ants in #16 to #20, ants that sink slightly in #16 to #20, and tiny flying ants that float low in #18 or #20. All can work on any body of water, but generally speaking the rougher and faster the water the larger and higher-floating the ant you can get away with. On the Yellowstone and all small streams, I seldom use anything but high-floating flying ants, while on Slough Creek I almost never do, for example. The low-floating tiny flying ants are strictly a late August or early September swarm, basically a hatch, that occasionally gets fish really excited on Slough Creek. These are unlikely to produce elsewhere. Otherwise, ants are a general-purpose pattern. As noted, sparse ants fished a few inches underwater work very well, particularly in flat water where the fish may see too many dry flies in general. Otherwise, fish ants dry.
Good basic patterns include the following:
All ants should be carried in cinnamon, black, and red/black combinations. Of these the cinnamon and red/black combo are generally more effective, probably because most commercial ants anglers bring are black.
Grasshoppers are the marquee summer terrestrial, the insect many visiting anglers hope and expect to match when they fly fish the Yellowstone area in late summer and early fall. Ants are more generally effective, but hoppers typically produce larger fish and more impressive strikes. Most anglers come expecting to fish big grasshoppers, patterns in the #6 to #10 range, often tied on 3xl hooks. Except in remote hike-in canyon water, as on portions of the Yellowstone River in its Black and Grand Canyons within Yellowstone Park, much smaller hoppers produce more fish, and they can produce big fish as well.
The small hoppers I'm discussing here are any that are tied on #10 standard length or #12 or smaller hooks. Basically, these are flies only large enough to float small or unweighted dropper nymphs. Don't hesitate to go tiny. My favorite small hoppers over the past several years have been tied on #14 standard-length hooks and #16 2xl or 3xl hooks.
Hoppers that fit in this category can work well on all waters, though they are generally less effective on spring creeks, lakes, and tailwaters than on freestone streams of any size or character. While they are usually more effective from mid-late morning through early evening on hot days with wind, basically when real grasshoppers are most active and likely to fall in the water, they can be effective at any time.
Good colors for small grasshoppers include "realistic" colors including cream, tan, gray, light brown, gold, and olive to much less realistic colors including various shades of pink, chartreuse, and bright yellow. Even purple or lilac can be good colors, particularly on overcast days. My best small hoppers since 2012 have been some shade of pink: baby doll pink as a general pattern, pale peach or flesh under bright sun, and dark pink first thing in the morning.
Favorite patterns include "fur and feather" patterns like the Letort Hopper, and Parachute Hopper, but foam patterns are now definitely more popular. Good choices include my Bob Hopper***, small Charlie Boy Hoppers, Grand Hoppers, and small sizes of Morrish Hoppers and Chubby Chernobyls. There's a lot of overlap between many of these patterns and large caddisflies, small stoneflies, perhaps large ants and beetles, and many basic attractor dry flies. This may explain some of their effectiveness. In other words, they look like more than just hoppers.
Small beetles, say from #12 to #18 or #20, always tied on standard-length hooks, are the "other" small terrestrial besides ants. I find ants generally more effective, but beetles can be good too. They are most effective on somewhat slower meadow streams, sometimes including spring creeks. The best color for this region is basic black, either in a standard Foam Beetle or a lower-floating deer hair Crowe Beetle. Other colors can also sometimes work, but black is the must-have. A #16 or #18 black beetle, of whatever pattern, does a good job of imitating the Mountain Pine Beetle, an insect that has kille large swathes of evergreens throughout the West. This is a native bug, but its populations have skyrocketed due to climate change (winters have not been cold enough to kill large numbers of them since the mid-1990s). This is bad for the woods but good for trout fishing.
Don't hesitate to fish foam beetle patterns when trout are rising to midges. They actually do a fair job of looking like a midge cluster, and they float a lot better than more-standard midge patterns.
Large grasshoppers, meaning any pattern size-10 or larger, generally tied on 2xl or 3xl hooks, are probably the single type of fly most visiting anglers think of when they think of fishing the Yellowstone area in late summer. As recently as the mid-2000s, such flies were the most consistent terrestrials one could fish on most waters through most of the summer. Since then, small hoppers and ants have become much more effective, probably due to increasing angling pressure and more-sophisticated fish, but big hoppers can still work wonders. This is particularly true if you're hoping to catch large trout on dry flies. Except for the three large species of stoneflies (Salmonfly, Golden Stone, and Midnight Stone), no other class of dry fly is as likely to produce fish over about 18 inches in length.
Large hoppers tend to work best either early, in late July, or late, in September. In the first case, this is probably because of overlap between many large hoppers and Midnight Stones and also because the trout have simply not been stung by large grasshoppers yet, while in September it's because that's when the hoppers have gotten as large as they'll get.
Good colors for large hoppers overlap with those mentioned above for small hoppers. More-natural tones generally work better except in remote areas of the Yellowstone River. This is a big change from about 2008-2010, when giant pink hoppers were some of our most effective flies. Overall, tan and gold tones are probably best. Especially in late July and early August, such colors make your hoppers also resemble Midnight Stones.
Good patterns include Grand Hoppers, Large Morrish Hoppers and the similar but fuzzier Yellowstoner, and various large Chubby Chernobyls. You should always fish these flies with a smaller dropper, either a beadhead nymph (including even #8-10 stonefly nymphs), or a smaller dry fly (attractor, caddis, ant, small hopper, or mayfly). Often trout will rise and look at a big hopper, but not eat it. The smaller "second chance" fly will then be impossible to resist, even though the fish might not have risen to this small fly if you had fished it by itself. This technique can produce very large trout. One of the best fish I ever had a client catch on the Yellowstone came up and nosed a huge hopper, then actually ate the #14 Clacka Caddis dangling 18 inches behind it.
Crickets and cicadas, here basically meaning any fairly large but not gigantic black terrestrial insect whether these are truly crickets and cicadas or not, are a changeup pattern from grasshoppers. Some years, the trout really love them, some years they don't. They are generally more effective early in terrestrial season (July) or late (September) than they are in October. They are also good choices whenever skies are dark, probably because they cast a darker and easier-to-see silhouette than hoppers during such situations. Appropriate sizes range from #8 or #10 down to #14, generally tied on long-shank hooks. Most good cricket/cicada patterns are tied with foam and have some sort of flashy or irridescent body material that breaks up the monotony of the foam. My favorites are Card's Cicada, black Foam PMX, and black over purple Chubby Chernobyls. The latter is either hyper-productive or will produce nothing, while the former two patterns will generally produce at least some action if the fish are looking for medium-large black terrestrials at all.
Spruce budworm moths, often just called spruce moths, are a small (#12 to #14) cream or blond moth that infests evergreen forests. This is another native bug whose numbers have climbed due to climate change. That said, they tend to be present in boom-and-bust cycles. Some years there are vast swarms that the trout will respond to selectively where evergreen forests come right down to the water's edge and opportunistically where there are even scattered evergreens, for as long as six weeks in late summer, while some years there's only a short window where trout that live in streams with abundant evergreens on the hillsides will eat them from time to time.
The most consistent spruce moth fishing is found on the Gallatin River, with upper Soda Butte Creek not too far behind. Various small streams that flow in evergreen forests also see consistent spruce moth fishing even in years when populations are not heavy. In such years, expect spruce moths primarily in the first half of August.
In years when spruce moth populations are heavy, they may interest trout in the waters just mentioned from about July 20 through at least Labor Day, if not a bit later. On other waters with even scattered evergreens, you might find fish eating them anytime in August. This includes places like the Yellowstone River through Livingston, where there are only scattered ornamental evergreen trees. If there are tons of spruce moths, even such limited habitat is enough to send fishable numbers of these bugs into rivers.
While trout will eat spruce moths throughout the day, the best fishing is usually in the afternoon and early evening, when these bugs may fall into the water like egg-laying aquatic insects.
Plan to carry two types of spruce moths: buoyant but low-floating patterns and less-buoyant patterns that can be fished either dry or "damp," just under the surface film, to imitate bugs that have fallen in the water and drowned. In the former category, I like Parachute Spruce Moths and my own Widow Spruce Moth***, while for damp flies, the best choice is definitely the Spent Spruce Moth***. When trout are only taking moths opportunistically, the high-floater works fine, much like any other buoyant terrestrial or attractor dry, while when falls are heavy they often prefer the flush-floating or even sinking fly.
Note that true meadow streams, including the Missouri River and most of the Yellowstone and Madison, basically anywhere that lacks any spruce, pine, or fir trees at all, will not have fishable numbers of moths no matter how heavy the yearly infestation is elsewhere.
While much less common than small beetles, a variety of much larger beetles are also present in the region. These are basically #10 to #14, on 2xl hooks. Chief among these is the Longhorn Beetle*** (both a real bug and a pattern) that can work wonders in the Lamar Drainage in August and September. There is probably somee overlap here with smaller cicada or cricket patterns, but you only neeed to see a couple actual longhorn beetles wandering around, with their giant antennae often replicated in patterns matching them, to recognize the trout will eat them if they get a chance.
Mormom crickets are huge, ugly insects. They're actually a ground-dwelling katydid rather than a cricket. Regardless of what you call them, they are an inch and a half to two inches in length, fat, and a sort of greasy gray-black or dark brown in color, with a lighter tan-gray underneath. They somewhat resemble large cockroaches both in color and in size. They live in burrows in the dirt, and can often be seen on dirt-covered slopes while you're hiking to the canyon sections of the Yellowstone, Gardner, and the Lamar and its tributaries. They are only important in the Lamar Drainage and on the Yellowstone, because these things are just too big for 95% of trout in the Gardner to eat. Look for them in late August and early September. Match them with #6 to #8 brown over tan Fat Alberts.
Bee imitations sometimes work quite well in the Lamar Drainage and on the Madison, even though there can't be all that many bees that screw up and fall in trout streams. I suspect these flies work at least partially due to the fact that few anglers think to try them, rather than because the trout are eating them regularly. Sometimes in heavily-pressured water, using something that's slightly different works just as well as something that's more like what the fish want. Whatever the reason trout eat bee patterns, use Foam Bees or CDC Bees in sizes #12 to #14.
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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