Southwest Montana and Yellowstone National Park Hatch Chart
Information on the insect hatches of the great fly fishing rivers in Southwest Montana and Yellowstone National Park.
STONEFLIES
While most anglers think of stoneflies as the large bugs hatching in huge numbers in the late spring, or the large weighted nymphs often used as much for their sink rate as their attractiveness to the trout, one must not overlook the importance of the nymphs through out the year, especially the smaller species which are very common. While great fishing can be had on Salmonflies and Big Goldens, similarly good fishing can also be had with small smaller golden or black stonefly nymphs all through the season. Often little Golden Stones are the go to nymphs in the fall and winter.
Salmon Fly (Pteronarcys californica) Hook size 4,6,8
These large stoneflies can provide epic fishing but are difficult hatches to time. It is usually worth the effort to fish several areas in a stream to track down the places where trout are most keyed into the big flies. Floating a big stretch of river is really the best approach. There are more Salmon Fly patterns than just about any other insect for western rivers, but the consistently productive flies all tend to be dull colored and slightly downsized.
| Madison (*E to QL) | June 25 through July 10 |
| Yellowstone | July 5 through July 25 |
| Gallatin | June 25 through July 20 |
| Henry’s Fork | May 25 through June |
Golden Stone (Hesperoperla pacifica) Hook size 6,8
These large goldens are often overlooked by anglers chasing Salmonflies. Don’t make the same mistake, as fish key on these insects long after their larger cousins have moved on. Throughout the early summer, a big golden stone makes a great searching pattern.
| Madison (*E to QL) | June 25 through July 15 |
| Yellowstone | July 1 through August 15 |
| Gallatin | June 25 through July 20 |
| Henry’s Fork | June 15 through July 15 |
Other Stoneflies Various species hooks sizes 12-18
Many species smaller species of stoneflies hatch in the Yellowstone area and are important to the fish. These can often be imitated with yellow and olive Stimulators in 14-16. Larger wingless nocturnal stones hatch on the Madison in late July and August. Seldom seen in large numbers, these #6-10 tan stones are something the fish look for throughout the mornings in the float section.
| Madison (*C & R) | June 20th through August 20th |
| Firehole | May 25th through June |
| Gallatin River | June 20th through August 1st |
| Yellowstone | July 15th through August 15th |
CADDISFLIES
Caddis (*Tricoptera-many species*) Hook size 12,14,16,18,20
Caddisflies are very important insects to imitate throughout the season. Reliable hatches can often be found after the bulk of the Mayfly species have hatched out, making fish key on the remaining Caddis. Emerger patterns are especially important on the Madison and Firehole Rivers. Subsurface imitation of Caddis larva and pupa is a useful tool in the nymphs fisherman’s arsenal.
| Madison (C & R) | June 20 through August 15 |
| Firehole | May 25 through June, September 1 through October |
| Yellowstone | July 15 through August 15 |
| Gallatin | July 1 through August 15 |
| Lamar & Slough Creek | July 1 through August 15 |
| Henry’s Fork | May 25 through September |
MAYFLIES
Mayflies provide classic fishing to rising trout from April through November in the Yellowstone area. They are found in all of our trout water and their imitations provide the core of our fly selections. In addition to the great match the hatch fishing which makes mayflies beloved by head hunting anglers, fish often respond well to mayfly patterns when they are used in a searching role. Mayfly nymphs are an important food source through out the year.
Pale Morning Dun (*Ephemerella inermis & infrequens*) Hook size 14,16,18,20
PMDs provide some of the best fishing of the season for dry fly anglers in the Yellowstone region. Look for insects to become smaller as hatches progress. Don’t ignore evening spinner falls for some really good fishing. PMD nymphs are also very effective during an emergence.
| Madison (YNP) | May 25 through June |
| Madison (*C & R) | June 25 through August 15 |
| Firehole | May 25 through June |
| Slough Creek | July 1 through July 20 |
| Yellowstone | July 15 through August |
| Henry’s Fork | June 1 through July |
Green Drake (Drunella grandis*) Hook size 10,12
Green Drake hatches seem as if they are tougher to hit than just about anything else, but if you get a cloudy day during the time of their peak activity, expect spectacular fishing. Always keep a few patterns on hand even if there is only an outside chance to find these flies. It does not take too many size 10 mayflies to get the fish looking to the surface.
| Yellowstone | July 20 through August 5 |
| Lamar & Slough Creek | August 25 through September |
| Henry’s Fork | June 15 through July 5 |
Brown Drake (Ephemera simulans) Hook size 8,10
Brown Drakes are often overshadowed by Green Drakes, but in general they are easier hatches to hit. Emergers, Duns and Spinners are all needed to cover a hatch. Look for them on warm calm evenings and expect to fish to rising fish well past dark.
| Gibbon | June 20 through July 10 |
| Henry’s Fork | June 20 through July 15 |
Gray Drake (Siphlonurus occidentalis) Hook size 10,12,14
Gray Drakes provide a lot of action with morning spinner falls.
| Slough Creek | July 1 through September 15 |
| Yellowstone | July 15 through September 15 |
Little Green Drake (Drunella flavilinea) Hook size 14,16
Flavs are a big deal on the Henry’s Fork, but they are often overshadowed in the mind of anglers on the Madison by PMDs. This is a big mistake. Their imitations are necessary not only for rising fish, but also make superb searching patterns.
| Madison (*C & R) | July 10 through August 10 |
| Firehole | June 10 through June 25 |
| Yellowstone | July 20 through August 10 |
| Henry’s Fork | July 1 through July 25 |
Callibaetis (Callibaetis nigritus) Hook size 14,16
These Mayflies can hatch in spectacular numbers on Hebgen Lake. Nymphs, emergers, duns and spinners are all keyed upon. Anglers underestimate just how finicky trout can be when they are rising in stagnate water to large quantities of insects. Carry multiple patterns and vary your approach.
| Hebgen Lake | July 15 through September 15 |
| Centennial Valley Lakes | July 1 through August |
| Henry’s Fork | August 1 through September 15 |
Tricos (*Tricorythodes minutus*) Hook size 18,20,22
Anglers expecting to find Callibaetis hatches are often surprised by the huge numbers of Tricos seen early in the mornings. These small bugs can be frustrating to fish, but early morning solitude amongst rising fish is easy to find.
| Hebgen Lake | July 15 through September 15 | |
| Madison (*YNP) | August 1 through September | |
| Henry’s Fork | August 1 through September |
Blue Winged Olives (*Baetis tricaudatus*) Hook size 16,18,20
If you are headed this way early or late in the season you need Baetis imitations. Cloudy days with a touch of rain or snow make for great hatches. Emergers and Duns are must haves, but one must not rule out the occasional spinner falls as a source of good fishing. Nymphs imitating BWOs are the best small nymphs on the Madison River throughout the fall, year after year.
| Madison (YNP) | May 25 through June, September 1 through October |
| Firehole | Same as Madison (*YNP) |
| Madison (*C & R) | May 1 through June 5, September 1 through November |
| Yellowstone | August 1 through October |
| Henry’s Fork | May 25 through October |
Tiny BWO (Baetis punctiventris) Hook size 20,22,24
You can love these tiny bugs, or you can let the difficulty in fishing them ruin your day. Regardless, when you come to this area in the fall, they may be your best chance to find dry fly fishing to steadily rising fish.
May 25 through June, September 1 through October
| Madison (*YNP) | |
| Firehole | Same as Madison (*YNP) |
| Henry’s Fork | June, September, October |
Other Mayflies
In addition to the “glory bugs” of the Mayfly world, there are other Mayflies which often provide good fishing on the rivers and lakes surrounding West Yellowstone. March Browns (12-14) are inconsistent early season finds down on the Madison (C & R) but when they are present, fish respond to them. Mid-day in April and May is the best time for hatches. The Madison has another little known bug of huge importance. Hatches of Epeorus mayflies begin in early July and last until nearly the end of August. Duns and nymphs are good flies to imitate, but it is the evening spinner falls of these insects which make for exceptional fishing. Early in the season they are often on the water along with PMD spinners, Flavs and a wide assortment of Caddis Flies. A generic rusty spinner fished in conjunction with a caddis emerger is deadly throughout the first three weeks in July. Once August rolls around, other bugs start to thin out and Epeorus spinner falls are hugely important to imitate and fish in the evening hours. Fish can often be found steadily rising to these insects well after dark, making for challenging and exciting fishing.
Midges
Midges make up a large part of the trout’s diet in the winter time. The Yellowstone area does not have a lot of streams on which midges are very important during the warmer months of the year, though an angler heading to Slough Creek in the summer should make sure to have a few patterns. Winter fishing is a different story. Any given day between November and March, provided the wind is not blowing, an angler can find midging trout on the Madison. Griffiths Gnats, Adams, as well as tan and black midge emergers in sizes 22-26 are the ticket to fooling these pod feeding fish. Only the calmest flows will hold rising fish. One trick to locate these areas is to observe where foam accumulates in the river and then search the water for subtle rises. Look for hatches and rising fish through the warmest part of the day. Many anglers are put off by the cold and difficulty of tracking the drift of the tiny fly in winter light. This is not easy fishing, but it is good, honest match the hatch dry fly fishing through the dog days of winter and for that, we can thank, rather than curse, our friend the midge.
Grasshoppers, Ants, Beetles, Crickets, Spruce Moths and Bees
Terrestrial insects have become have become synonymous with late summer fishing out west. “Hopper season” is how August is summed up for many anglers for good reason. However, as fish become more pressured, they become increasingly immune to large terrestrials. Instead of #4 hoppers and big foam Chernobyl style ants, we often find ourselves fishing #14 hoppers and tiny #18 ants. Dry summers grow bigger hoppers on the whole, though many different types of hoppers are often available at any one time. As with everything else, it is important to match the naturals. Do not just tie on a #6 Club Sandwich because it pounded on fish last summer. While hoppers often bring the headlines, ants and beetles account for more fish. Be sure to keep these smaller bugs on hand. Flying ants, when encountered, can make for once in a lifetime fishing. Crickets, Spruce Moths and Bees are less common, but fish can be selective to all three. If you are headed this way from July 15 through September 30 expect to fish terrestrials as a primary option.
This chart is not intended to be comprehensive. It lists only what we consider to be the most important hatches of aquatic insects for dry fly fishing as they occur during the season. Hatch dates can vary from year to year depending on duration of runoff and water temperatures.
*YNP—-Yellowstone National Park
*C & R—-Catch and release section in Montana
*E to QL—-Ennis to Quake Lake section in Montana