Insect Hatches on the Missouri River

The Missouri River’s cold, consistent flows below Holter and Hauser Dam create the perfect conditions for prolific hatches. From early spring through the dead of winter, the river provides anglers with a steady stream of dry fly opportunities, nymphing action, and even some exceptional streamer fishing. Understanding the seasonal hatches can make the difference between a good day and an unforgettable one. Here’s a look at the primary insect hatches on the Missouri River, broken down by season, along with the best fly patterns to match them.

Spring Hatches (April – May)

As winter begins to loosen its grip on Montana, the Missouri River comes alive with the first major hatches of the year. Water temperatures rise, days lengthen, and trout begin feeding heavily to recover from the lean winter months.

Midges 

Midges are a year-round food source on the Missouri, but in the early months of spring – March, and into April—they can blanket the river. These tiny insects emerge in vast numbers, clustering on the surface in tight groups. This behavior makes them an easy target for rising trout, which sip them methodically in the softer edges, back eddies, and foam lines. On calm days, dry fly fishing with tiny midge patterns and clusters can be incredible.

• Best Fly Patterns:
  • Griffith’s Gnat (#18-22)
  • Cluster Midge (#18-22)
  • Zebra Midge (Black, Red, Olive) (#18-22)
  • RS2 (Gray, Olive, Black) (#18-22)

Blue-Winged Olives (BWOs) (March – May)

Blue – wing olives (Baetis) are a staple in the diet of Missouri River trout. These mayflies typically range in size from 16 to 20, with a distinct olive body and slate-gray wings. The spring hatch generally kicks off when water temperatures hover around the mid – 40s. 

BWOs are one of the most anticipated spring hatches. When these small mayflies emerge on overcast days, it can be pure magic.

• Best Fly Patterns:
  • BWO Sparkle Dun (#18-20)
  • 401k Baetis (#18-20)
  • Parachute Adams (#16-20)
  • Two Bit Hooker (#18-20)
  • Pheasant Tail Nymph (#16-20)
  • Little Green Machine (#16-20)

March Browns (April – Early May)

Larger mayflies start showing up by mid-April. March Browns hatch sporadically and are not a very big hatch on the Missouri River.

• Best Fly Patterns:
  • March Brown Cripple (#12-14)
  • Parachute March Brown (#12-14)
  • Hare’s Ear Nymph (#12-14)
  • Soft Hackle Pheasant Tail (#12-14)

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Summer Hatches (June – Sept.)

With the Missouri’s legendary summer hatches, anglers experience some of the best dry fly fishing in the world.

Pale Morning Duns (PMDs) (June – Early August)

The PMD is one of the most anticipated insect hatches on the Missouri River. PMD mayflies keep trout rising consistently to emergers, cripples, and spinners, favoring easy meals over actively escaping duns.

• Best Fly Patterns:
  • PMD Sparkle Dun (#16-18)
  • Film Critic PMD (#16-18)
  • Hi -Vis Spinner  PMD (#16-18)
  • PMD Nymphs like Split Case PMD (#16-18)

Caddisflies (June – September)

Unlike mayflies, which typically float delicately on the water’s surface, caddisflies are known for their erratic movements. They skitter and bounce, often bringing aggressive surface action. . 

• Best Fly Patterns:
  • X-Caddis (#14-18)
  • Elk Hair Caddis (#14-18)
  • Soft Hackle Caddis Pupa (#14-18)
  • Corn-fed Caddis – A Missouri River favorite, designed for picky trout.
  • Translucent Caddis Pupa Tan #14-18

Terrestrials – Hoppers, Ants, and Beetles (July – September)

Terrestrial fishing on the Missouri River offers some of the most exciting dry fly action of the year. During the heat of summer, big trout love meaty meals drifting near the banks and faster rifles. 

• Best Fly Patterns:
  • Morrish Hopper (#10-14)
  • Parachute Ant (Black, Red) (#14-18)
  • Foam Beetle (#14-18)
  • Chubby Chernobyl (#10-14)

Tricos (August – September)

Tricorythodes, or Tricos for Tricorythodes, are small mayflies that hatch in prolific numbers on the Missouri River from mid-July through September. The spinner fall of these tiny mayflies is what drives trout into feeding frenzies, offering anglers some of the most technical dry fly fishing of the year. Focus on the drift rather than the fly selection. Ants, caddis, and midge clusters will all work on Trico-eating fish.

• Best Fly Patterns:
  • Trico Spinner (#20-22)
  • Trico Parachute (#20-22)
  • Griffith’s Gnat or Buzzball  (#14-20)
  • Trico Emerger (#20-22)

Fall Insect Hatches on the Missouri River

As temperatures drop, hatches shift back to the Baetis and Caddis, trout continue to feed aggressively to bulk up before winter.

Fall Blue-Winged Olives (BWOs) (September – November)

BWOs make their return as water temperatures drop. These hatches often provide some fantastic dry fly fishing.

• Best Fly Patterns:
  • Parachute Adams (#18-22)
  • BWO Comparadun (#18-22)
  • BWO Film Critic (#18-22)
  • Pheasant Tail Nymph (#18-22)

October Caddis (October- November )

October caddis are the largest caddisflies found on the Missouri River. With their pumpkin-orange bodies and oversized wings, they are impossible to miss when fluttering over the water. Unlike the blanket hatches of PMDs or caddis of summer, the October caddis tend to hatch sporadically.

This large caddis are a favorite for aggressive trout.

• Best Fly Patterns:
  • Orange Stimulator (#8-12)
  • Orange Chubby (#8-12)
  • Elk Hair Caddis (Orange) (#8-12)
  • Soft Hackle October Caddis (#8-12)

Winter Hatches on the Missouri

Fishing the Missouri River in winter can be cold, but the rewards are worth it for dedicated anglers willing to brave the elements.

Midges (Year-Round)

Midges are the primary insect activity during winter on the Missouri River. These tiny insects, often black, gray, or olive in color, emerge in steady numbers on calm days, typically during the warmest part of the afternoon. When the wind lays down, and the surface of the river turns to glass, you might notice clusters of midges forming, drifting in slow seams, or gathering in eddies.

• Best Fly Patterns:
  • Griffith’s Gnat (#16-18)
  • Cluster Midge (#14-20)
  • Zebra Midge (#18-22)
  • RS2 (#18-20)

Conclusion

Understanding the Missouri River’s seasonal hatches and having the right fly patterns are crucial for success. Spring brings midges, BWOs, and March Browns. Summer is all about PMDs, caddis, and terrestrial fishing. Fall sees the return of BWOs, tricos, and October Caddis. And winter, though quieter, still offers excellent midge fishing. For the dedicated fly angler, the Missouri River is a year-round fishery, offering some of the best fishing opportunities anywhere. Tight lines!