Like any high-quality freestone river, the Yellowstone River supports a wide variety of aquatic (and terrestrial) insects. However, some of those bugs are more important than others to the fly angler. If you are preparing to fly fish the Yellowstone River, the following list of major hatches will help prepare you for what you might find.
Midges can be found in the Yellowstone River all year round, however you will not find them on the end of most anglers’ lines until the late fall and winter months. Midges are tied and fished both as nymphs and dry flies. Midges can range in size anywhere from a 16 all the way down to a 24. November through March, the fish of the Yellowstone are keyed in on midge nymphs nearly the entire length of the river. Dry fly midge fishing is best done in the soft water near the banks, and with any luck an angler can find a foam pocket to fish midge clusters (mating midges) near the river’s edge because the fish key in on these pockets as food accumulates there.
Midge flies are typically fished in black, red, or cream colors. Nymph patterns that are successful on the Yellowstone are the Z-Bro Midge, Brassie, Minute Midge, Midge Larvae, and the Miracle Nymph. For dry flies, try Renegades, Dom’s Midge Hanger, Willie’s Double G, Griffiths Gnat, Micro Midge, Sprout Midge, CDC Cluster, or a Hanging Midge.
Mothers Day Caddis
One of the most famous hatches to come off of the Yellowstone River is the American Grannom, most commonly referred to as the Mothers Day Caddis. These bugs come off so thick at times that they form a literal blanket over the water, which can be over an inch thick. The tough part about the Mothers Day Caddis is that the hatch is in a race with run-off. Some years the caddis hatch works out perfect, other years the water rises too early and anglers do not get to take advantage of this amazing hatch. The bugs usually start coming off in smaller numbers around the third week of April, and it will typically run into the second week of May. The adult version has a black body, with an olive colored rear end.
Nymphs we like to fish for this hatch include the Mangy Caddis Pupae, Morrish’s Dirty Bird, and Morrish’s Super Pupae. For dry flies, we turn to the Henryville Caddis, Elk hair Mothers Day Caddis, and the Spotlight Caddis.
The biggest dry fly we get to fish here in Montana is the Salmon Fly. When there are rumors of these big bugs hatching, the phone at the shop rings off of the hook all day. It is a short lived hatch that starts typically in Paradise Valley, and works its way up river (South) to Gardiner in a couple weeks time. Typically the Salmon Flies start in the very early part of July. This is another hatch that is hard to time. Whether the river is high or not, dirty or clear, these bugs will come off; the question is that if the river is safe enough to fish by the time these bugs are doing their thing.
Popular nymphs used to imitate Salmon Flies are Yuk Bugs, Bitch Creek Stones, Rubber legs, and Woolly Buggers. Dry flies we like to throw include the Flutter Bug, Totally Stoned: Salmon Fly, Sofa Pillow, Dog Puke, and South Fork Secret.
The Golden Stonefly is another prolific hatch that occurs on the Yellowstone. They can come off of the water any time from late June to Early August, but the nymphs are always in the river, and typically a good choice to run as a point fly. Stoneflies thrive in rocky habitat, making the Yellowstone River a perfect environment for this bug. Golden Stones can be found from Gardiner all they way down to Billings. Golden Stone adults can range in sizes between 6 and 12, and the same goes for the nymphs.
Nymph imitations include the Rock N’ Roller Stone, Rubber Legs, Jimmy Legs, and Bead head Golden Stones. For dry flies the most commonly flies are the Chubby Chernobyl in gold, Drowned Golden Stone, Totally Stoned Golden, the X-fly Cat Puke, and Yellow Stimulators.
The Yellow Sallie, like the Golden Stone and Salmon Fly, is another form of stonefly. Their bodies can either be straight yellow or have a pinkish orange hue on the rear end of the bug. Sallies come off of the Yellowstone starting in mid July and extending well into August most years. The Yellow Sallies are much smaller than their cousins the Golden and Salmon fly. Both nymphs and dries are fished in sizes 12 through 18.
Nymphs that are commonly fished to imitate Sallies include the Kyle’s Bead head Yellow Sallie, Psycho Prince, Gabriel’s Trumpet, and the Tungsten Sallie. Dry flies used include Yellow Stimulators, Hair wing Yellow Sallie, Yellow Sallie Rolling Stone, Berret’s Hairy Yellow Sallie, and Berret’s CDC Yellow Sallie.
Terrestrials are insects that are not born in the water but on land. In the Yellowstone they include grasshoppers, ants, and beetles. August into October is the time when these types of patterns are successful on the Yellowstone. Since these bugs are not born in the water, we only fish the dry fly form of them. Terrestrial fishing is special; it can provoke some big fish to eat dry flies, making them a preferred insect to imitate for fly anglers. There are hundreds of terrestrial variations to choose from to fish. Another special thing about terrestrials is that sometimes it is better to twitch the fly, making it a more active form of dry fly fishing, which some people really enjoy. For grasshopper patterns think about trying the Morrish Hopper, Chaos Hopper, Thunder Thighs, Panty Dropper Hopper, or a Sweetgrass Hopper. Body colors for these bugs include pink, gold, green, tan, brown, and red. When it comes to ants, we fish both cinnamon colored ants and black ants. Patterns to consider are the Power Ant, Parachute Ant, Hi-Vis Ant, and the Water Wasp. Beetles come in a variety of colors as well; brown, black, and green are the most common that you will see. Fat Albert, Crystal Flash Foam Beetles, Grillo’s Hippie Stomper, the X-tra Terrestrial, and Yeager’s 409 all are great choices to imitate beetles.
Baetis (Blue-Winged Olives)
Baetis are a bug that can be found almost every month of the year on the Yellowstone. But September and October are the best times to find them on the water. Baetis hatch most prominently on overcast days with higher humidity. They are commonly called blue winged olives, which can be misleading because Baetis may have a grey or tan body as well. The insect itself is small, typically a size 16-22, but they sure do come off in large numbers when conditions are right. Baetis nymphs are active swimmers, and are found river wide, but are most prolific in weedy riffle runs. It is best to nymph with them deeper in the morning, then mid day fish a floating nymph, towards the afternoon the emergence occurs, and then when they are seen on the surface, go to a dun.
Nymph patterns we like for Baetis include the Juju Baetis, Olive Pheasant Tail, Cold Turkey Baetis, and the BWO Nymph. Dries that imitate the Baetis well are the BWO Comparadun, Sparkle Stacker, BWO Biot Parachute, and the Baetis Sprout.
Pale Morning Dun (PMD)
The Pale Morning Dun, or PMD, which is what anglers refer to them as, are a mayfly that are found in June, July, August, and sometimes into early September on the Yellowstone River. They also vary in color from an olive-brown to a red-brown. They are fished from a size 14 to 20, and have some of the most prolific spinner falls on the Yellowstone. Hatches can occur in the morning, afternoon, and evening, making their name a little bit misleading. They typically hatch in slow, clear water, making tippet selection important when fishing these bugs.
Nymphs used to imitate the Pale Morning Dun include the Sawyer’s Pheasant Tail, Split-Case PMD, Floating PMD Nymph, and the PMD Thread Nymph. Dry flies commonly fished are the CDC Thorax PMD, Knock down Dun, Captive PMD Dun, and a Parachute PMD. The spinner best fished for this bug is typically a Rusty Spinner.
Streamers are flies that are used to imitate smaller fish, Leeches, and Crayfish. In the Yellowstone we use streamers to imitate Sculpins, baby Brown, Rainbow, and Cutthroat Trout, as well as baby Whitefish. Streamer flies can be effective 12 months of the year on this River. In the spring, prior to run off, streamers are very effective for fish looking for bigger meals after a winter of eating midges. Just after run off, streamers are fished against the slow water on the banks, offering the fish a big, easy to eat meal. In the fall, when Brown Trout are getting ready to spawn, they get very aggressive and predatory toward smaller fish, making streamers an excellent choice. Overcast days are preferred for streamer fishing; however, fish will eat them in almost every light condition.
To imitate Sculpins, patterns such as the Butt Monkey, Zoo Cougar, Morrish Sculpin, Silvey’s Sculpin Leech, and McCune’s Sculpin are very effective. For baby trout, the Sparkle Minnow, Double Bunny, and Mirrored Minnow are excellent choices. To mock Leeches, Woolly Buggers, Mo-Hair Leeches, Slump Busters, and Strung Out Leeches. As for Crayfish, Bush’s Dad, The Thing, and The Big Nasty are all great patterns to try.1