There's no doubt that mayflies, caddisflies, and stoneflies are the most important insects to trout anglers in the Yellowstone Area, except perhaps in the dead of winter. That said, there are other insects the trout eat, as well. This page provides a brief overview of these insects. It is divided into two sections: midges and "other." It should be fairly obvious from this division that midges are quite a bit more important than any other single type of "other" trout water insects besides mayflies, caddis, and stoneflies.
Note that scuds (freshwater shrimp) and sowbugs are discussed on the Other Trout Food page, since these are not actually insects even if they are rather creepy-crawly. Also note that terrestrial insects that might fall prey to trout after taking an unintended bath get their own page.
The following table covers important midges and other insects in the region, beginning with midges, then covering other food items. Note that this is a general chart. Crucial insects 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 hatch charts specific to all area waters.
If you wish to print a full-size version of this hatch chart, those covering other insects and food items important when fly fishing the Yellowstone area, and all other charts on this site, please visit this link.
Midges are much, much less important to anglers visiting the Yellowstone area and even areas of southern Montana including the Missouri River tailwater than they are in many other areas of the United States. Some anglers may be used to fishing almost nothing except midge imitations on their home waters. Except in winter or perhaps on a few unlucky days on the Paradise Valley spring creeks or area tailwaters, the situation around here is almost the exact opposite. Most of the time, you need not even think about tying on a midge, either a dry fly or a nymph. When you do need to fish a midge around here, you'll be pleasantly surprised to learn they are usually big, as far as midges go, #18 instead of teeny-tiny.
There is one specific body of water and two general types of water where you should expect to fish midges as a bread and butter fly any time except the dead of winter. These are (first and foremost) the Missouri River tailwaters below Hauser and Holter Dams, especially below Holter Dam, the Paradise Valley spring creeks and other regional spring-fed streams, and shallow, weedy lakes whether these are the private ranch lakes or public (primarily hike-in) lakes.
On the Missouri, midge imitations of one type or another are most important through the winter and in early spring, before the middle of May when heavy mayfly hatches usually begin and the water can begin getting very high, too high for fish to want to rise. On the "MO," fish seldom rise to single midges, but it's a good idea to have a few in black, olive, and gray in #20 or so. More commonly, fish will rise to clusters of midges, especially in areas where they collect heavily, such as in eddies. It takes a lot of midges to get the trout rising here, but when they do, it can be outstanding. This is mostly likely to happen in late April and early May when winds are calm, usually in early evening on warm days. Through the winter, midge larvae and pupae are good choices, particularly as a dropper nymph behind a larger scud or sowbug pattern.
On the spring creeks, midges are most important from November through March, late May and early June, and late August through perhaps the first week of October. These are all periods when mayfly hatches are limited. Both subsurface larvae and pupae are important, and you may occasionally find fish rising to single midges, particularly in shallow, slow water. Clusters are less important overall. The midges that the trout fixate on in spring creeks may be small, down to #24. Olive, black, tan, white, gray, and red may all be important colors. All in all, midge fishing in the spring creeks is much more comparable to midge fishing in parts of the United States where this is a standard tactic than it is to midging elsewhere in the Yellowstone area.
"Specific midges" is a bit of a misnomer. In reality, what I'm talking about in this situation are some specific situations in which it's a good idea to plan to have and fish midge patterns: what to look for and what to use.
On all area rivers that are open in the winter, midges are often the best or even only food source. This is particularly true during the absolute dead of winter, late December and January. At this time, very few food items are present and active in rivers except midges. On all of them, fish Zebra Midges, WD-40s (which also double as a BWO nymph), Love Bugs, Disco Midges, and other similar generic midge larva and pupa patterns. Good larva/pupa colors are black, olive, red, and gray. If there's any color in the water at all, make sure to use midge larvae/pupae with a bit of flash. On calm days when temperatures are in the 30s or 40s, you may also find rising fish. At this time, cluster midges like Griffith's Gnats are good choices when there are large numbers of visible midges. If you are seeing only a few, instead use Zelon Midges*** or PFS Bastard Midges***. Dry midge patterns should be #18 to #22 and dark olive to black in color. There can be sufficient midges out on the Yellowstone and Madison for strong fishing, particularly in late January and February. The insects that hatch at this time are locally known as Snow Flies.
This insect is present primarily in the Yellowstone River and is very large, about #14 or #16. While it's possible this is a cranefly rather than a midge, I doubt it. This bug is almost straight black. Very, very occasionally enough of these bugs hatch that the fish will rise selectively towards them. This presents a problem since they are quite different than other insects that hatch at the same time (larger stoneflies and caddis, mostly). If you do believe the fish are eating these, try a Black Gnat or a large black caddis pattern of some kind.
The only flowing water in Yellowstone Park where midges are a relatively common food source (at least during the legal season rather than winter) is the Lamar River Drainage. Here, dark olive to black midges can draw action in the latter half of August and first half of September. If you see fish rising very slowly and lazily in shallow tailouts on late summer or early fall mornings, this is probably what they are taking. These insects are easy to mistake for Trico mayflies. Trico patterns even sometimes work. A better dry is the Lamar Midge*** in #18 or #20. This pattern has a black body, white CDC caddis-style wing with a bit of flash, and grizzly hackle. When these insects are about, a Zebra Midge*** is a good choice when nymphing. Black with a copper rib seems to be the best combination. Dredge this in the deepest holes behind some kind of mayfly nymph.
As noted above, on the Missouri larvae and pupae make good dropper nymphs behind something bigger. Depending on season, this other fly may be a San Juan Worm, a mayfly nymph, an egg, a standard sow bug or scud pattern, or one of several Czech nymphs (Rainbow Czech or Amex Czech are favorites) that look like a gob of generic food, whether a scud, sowbug, egg, or caddis larva is up to the trout. This is usually a winter-only tactic, and the prevalance of the "gob of food" Czech nymphs I just mentioned is why: much of the season there are plenty of larger subsurface food items available. When they are on subsurface midges, #18 or #20 Zebra Midges in red or black (or a combination of the two), Disco Midges, Love Bugs***, tiny Grape Slushies***, and red Brassies are good choices. For dries, you may get a fish now and again on a single midge in size-18 or size-20, but cluster patterns are far better. Griffith's Gnats and the similar pattern called the Snow Woolly*** are good, but a real favorite is the Buzzball. Don't hesitate to go big with these: #16 is not out of the realm of possibility. Dead-winter dry fly fishing is poor on the Missouri. Look for more rising trout eating midges from March through mid-May than earlier; there's just enough subsurface food in this tailwater that they don't like to rise when the water is ice-cold.
Spring creek midges should be small and sparse. As noted, they are good choices primarily when nothing else is happening: during the winter, for a brief period around Memorial Day, and in late summer and early fall. Thread-bodied midge are best, perhaps with a bead, perhaps not. Perhaps with flash, perhaps not. The ever-popular black or red or black/red Zebra Midge is a reasonable choice, but tan, olive, gray, and cream might also work. Use thin and non-obvious ribs (7X tippet or thread) on some. The spring creeks are the only place in the regionwhere you will probably need to fish a single midge dry rather than a cluster if the fish are rising. Zelon Midges*** and Lamar Midges*** are good choices, in olive, gray, or black. Expect better midge dry fly fishing in the winter, up to March 15 or so, than at other times of year, when if the fish are rising well it is usually to mayflies.
Chironomids are simply large lake-dwelling midges. They can range from a #10 3xl hook all the way down to a #14 or #16 standard-shank hook. They are most important, both subsurface and as dry flies, from May through July, though they can be present before and after this period as well. Fish beadhead larval/pupal patterns like Merrell Lake Bombers*** or other "Ice Cream Cone" or "Bomber" style patterns either under an indicator just off weed beds or with a slow hand-twist retrieve. If you are seeing occasional aggressive rises, switch to a Stillwater Softy***, Woody, Kaufmann Chironomid, or unweighted Prince. Strip these aggressively, either deep behind a leech or streamer or just under the surface. A Driscoll's Midge*** is good both under an indicator and stripped. The best dry fly fishing will occur when winds are calm, at mid-late morning. Use small Coachman Trudes, Parachute Adams, or large Griffith's Gnats. Aim for specific fish when you can. On lakes containing grayling or brook trout, don't hesitate to strip your dry chironomid through the surface film so it cuts a wake.
All of the following bugs are important only rarely, usually in certain specific waters or at least types of water. That said, if you know you'll be fishing a body of water that has these insects at the timeframe in which they can be important, it's a good idea to carry a few.
Damselflies are by far the most important "other" bug in the Yellowstone area. They inhabit all fertile, weedy lakes regardless of elevation, and can also occasionally be important on fertile, weedy, slow-moving rivers as well, slow sections of the Firehole being the chief example. They hatch from May through July, with June the most important month overall. Nymphs are generally more important, but when heavy hatches occur the trout may rise aggressively to them, even jumping out of the water after damsels hovering up to a foot above the water. Our damselflies are olive to chartreuse green in color as nymphs and usually blue as adults, about a size-12 or size-14.
Fish damsel nymphs by stripping them erratically towards shore. When they hatch, all damsels swim directly towards the bank, a stick, or some other place where they can climb out of the water to shed their nymphal shucks. Good damsel patterns all have tails or abdomens that suggest the slender, wiggling action of the naturals' abdomen. You can fish damsel nymphs under an indicator or without.
Adult damselflies should be tied on short-shank hooks with white wings and long, slender extended bodies. Only use them when you see fish rising aggressively and many damsels in the air. The best fishing will be when slight breezes push the natural insects close to the water, particularly near cattails or other acquatic vegetation that sticks up out of the water.
As adults, craneflies resemble giant mosquitoes and skitter along the water. Occasionally these draw explosive strikes. This is most likely to occur on slow-moving, silt-bodied waters such as the Lower Madison and slower portions of the Yellowstone downstream of Yellowstone Park, particularly in the morning. Cranefly larvae can be more important. These somewhat resemble very large caddis larvae, with a major distinction being that cranefly imitations must be tied with many trailing fibers, picked out dubbing, etc. to suggest the gills of the naturals. You can also tie upsized scud patterns, again with the bodies picked out. These are large insects, #4 to #10, 2xl or 3xl hooks, so if the trout are eating them, you might move some big fish. Good colors are pale: white, cream, light gray, tan, and gray-olive. Cranefly larvae live in bottom sediment, so the tail end of runoff is a good time to fish them, as they may be washed out at this time, and the large size makes them visible to the fish in dirty water.
These aquatic insects resemble beetles. While they may be found in slow-moving sections of river, they are only ever important in lakes, especially fertile low-elevation lakes. They are never or almost never "the" fly, bu they can be a good changeup pattern through the summer months and into early fall. Fish patterns matching them (Google is your friend for ideas) with an erratic strip so that they rise up from the bottom. A chironomid, soft hackle, or Callibaetis nymph makes a good dropper, or you can fish the boatman or backswimmer as a dropper behind a larger leech or streamer.
You will see dragonflies from time to time, but I must say I've never caught a fish in the Yellowstone area on one, an adult or a nymph. That said, West Yellowstone legend Charlie Brooks advocated his Assam Dragon nymph pattern in both lakes and slow-moving sections of river like lower Slough Creek, so you never know.
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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