Firehole River Fly Hatch Chart

A robust and diverse population of aquatic insects and fly hatches makes Firehole River one of the most productive dry fly trout fishing rivers in the United States.

firehole river fly hatch chart

Firehole River Hatch Chart

The following chart lists the most important hatches that anglers should plan for to when fishing the Firehole River. Fly sizes and hatches date will vary by river section and conditions.

Fly HatchSizeDate
March Brown10–14Apr 20 - June 5
Midges18–22May 20 - Oct 31
Blue-winged Olive (Baetis)16–24May 20 - June 15; Sep 1 - Oct 31
Little Blue-winged Olive18–24May 20 - June 30; Sep 1 - Oct 31
Little Black Caddis (American Grannom)16–18May 25 - June 15; Sep 1 - Sep 20
Small Western Green Drake12–16June 1 - June 30
Flavs14–16June 1 - June 30
Salmonfly2–8June 1 - July 15
Golden Stonefly6–10June 1 - July 15
Yellow Sally14–16June 1 - July 15
PMDs16–20June 1 - July 10
Little Brown Caddis18June 5 - July 15
Spotted Sedges14–16June 5 - Aug 31
White Miller16June; Aug 1 - Sept 20
Maghoney Duns14–18June 10 - July 31
Speckled Peter20June 15 - July 15
Little Yellow Sallies10–12June 15 - Aug 5
Little Black Short Horned Sedges20–22June 20 - Aug 31
Brown Drakes10–12June 25 - July 15
Grasshoppers10–14July 1 - Oct 15
Crickets12–16July 1 - Oct 15
Ants16–18July 1 - Oct 15
Beetles14–18July 1 - Oct 15
Green Sedges14–18July 1 - Oct 31
Little Sister Caddis18–22July 15 - Aug 31
Longhorn Sedge16Aug 20 - Oct 15

Major Firehole River Hatches

The first major fly hatches of the year on Firehole River will be midges followed by Blue Winged Olives (BWOs). Midge hatches get underway as early as late April and continue through early June. BWO hatches appear in late May and continue through mid June, reappearing in early fall. A simple #14-16 Parachute Adams is your go-to fly for fishing both of these hatches.

As weather warms in June, attention turns to Pale Morning Dun (PMD) mayfly and caddis hatches as the river comes to life with aquatic insects. PMD hatches are hot and heavy from the bigging of June through mid July. Caddis hatches get under way in June as well and linger throughout the summer. A size #16-18 cripple pattern or PMD imitation fly is effective for fishing the PMD hatch.

The most important caddis fly to pay attention to is the White Miller. This large, cream-colored insect is a trout delicacy. During early afternoons you’ll see trout breaking the surface to get a mouthful of this delectable fly. A #10-12 White Miller pattern that floats is your go-to fly to match the hatch. You can pick up this fly at a local fly shop or pre order online.

June ushers in another important fly hatch, Yellow Sally stoneflies. Yellow sally hatches peak during the month of June and linger through July and into August some years. Terrestrials enter the fray beginning of July and every angler should carry a good supply of ant, beetle and hopper patterns sizes #10-18.

Caddis hatches reappear in force as soon as the cool weather hits in September. Moving into late fall, early winter as temperatures plummet, and snow moves in, BWO and midge hatches again take center stage. During spring and fall anglers should be prepared with an array of patterns to target caddis, BWO and midge hatches. Downsize your fly size for fall fishing.

On the Firehole River, a slight change in temperature or cloud cover from one day to the next can change the predominant hatch on the water. One of the most effective presentations for fly fishing Firestone River is an emerger patterned fished behind a dry fly.