Short answer: Green Drakes are the largest mayflies most trout anglers will ever fish — hook sizes 8 to 12, olive-green bodies, big slate-grey wings. They hatch for a couple of weeks in early summer, they bring the biggest fish in the river to the surface, and the hatch is short enough that people plan their entire year around catching it.

If the PMD is the reliable workhorse, the Green Drake is the event. It's the hatch where a fish that has spent all season eating size 18 nymphs decides a mouthful is worth the risk, and the takes are correspondingly violent.

What a Green Drake actually is

Like most angler names, this one covers more than one insect.

Western Green Drake — Drunella grandis and Drunella doddsii. Hook sizes 10 to 12, dark olive body, slate wings. This is the one that makes the Henry's Fork famous.

Eastern Green Drake — Ephemera guttulata. Bigger still at sizes 8 to 10, with a pale cream-yellow body and heavily mottled wings. Its spinner is the legendary Coffin Fly, white-bodied and unmistakable.

Two quite different insects, both enormous, both producing the same reaction from trout.

Size — 8 to 12. In the hand a Green Drake dun looks absurd next to a PMD.
Body — olive to olive-green in the West, cream-yellow in the East.
Wings — tall, slate-grey to heavily mottled, and very visible on the water.
Nymph — a stout crawler in the West; a burrowing nymph in the East that lives in silt and swims poorly.

Fig. 1 — The Green Drake cycle. Everything about it is oversized.

Key to the stages

Nymph

Large and stout, sizes 8-12. Western crawler; eastern burrower in silt.

Emerger

A big insect takes a long time to get free. Often the most productive stage.

Dun

Tall slate wings, olive body. Big enough to see at forty feet.

Spinner

In the East this is the Coffin Fly — stark white body, unmistakable at dusk.

Spent spinner

Evening fall. On eastern rivers the Coffin Fly fall is its own event.

Why big fish behave differently

A large trout does arithmetic. Rising to a size 20 costs more energy than the insect returns, which is why the best fish in a pool often ignore a heavy PMD hatch entirely and eat nymphs all day. A Green Drake changes the maths — one mouthful is worth the trip. That is why this hatch produces fish you didn't know the river held, and why it's worth abandoning good PMD water to go and find it.

When it happens

Green Drakes come off in early summer as water settles after runoff, generally in the high 50s Fahrenheit. The hatch is famously short — often ten days to a fortnight on a given stretch — and famously weather-dependent. Cool, damp, overcast days produce the heaviest emergences.

Region	May	Jun	Jul	Aug
Idaho — Henry's Fork		Peak	On
Colorado — Roaring Fork, Frying Pan		On	Peak	On
Montana — Madison, Bitterroot		Peak	On
Wyoming — Snake system		On	Peak
Catskills — eastern drake	On	Peak
Pennsylvania — eastern drake	Peak	On

Peak Active

Elevation matters more here than almost any other hatch. On a single Colorado drainage the drakes can start in the lower canyon in June and still be going high up the valley in August, so a river that's finished at one access point may be perfect twenty miles upstream.

How to fish it

Go heavier. A size 10 dun on 6X is a bad idea. 3X or 4X, a 5 or 6-weight rod, and a leader that turns over a big air-resistant fly. See our tippets and rod and reel combos.

Expect fewer, better fish. This isn't a numbers hatch. You may get six shots in an afternoon, and three of them will be at the largest trout you've seen all year. Treat each one accordingly.

Don't set fast. Big fish take a big fly slowly and deliberately. The classic error is pulling the fly out of an open mouth. Say a word to yourself before you lift.

Fish the emerger when duns get refused. A drake takes a long time to escape its shuck, and pressured fish learn to eat the cripple rather than the dun. If perfect drifts are being ignored, that's your answer.

Stay for the spinner fall. Eastern anglers know this — the Coffin Fly fall at dusk can be better than the hatch itself, and it happens when everyone else has gone to dinner.

Common mistakes

Fishing tippet that's too fine. You will lose the fish of the season to 6X.

Striking too quickly. Covered above, and it's the one people regret for years.

Chasing the calendar instead of the elevation. If the hatch is over where you are, go upstream and up in elevation rather than home.

Fishing only the dun. The emerger and the spinner both produce, and both get ignored.

Flies to carry

Big drake patterns in 10 and 12, plus an emerger and a spent spinner. Sizes matter more than exact colour here — silhouette does the work.

The Postfly First Cast Beginner Dry Flies Assortment and the Fly Rod Chronicles Dry Fly 12pk cover the surface range, and the Adams Classic Dry Fly in its largest size is a serviceable drake silhouette in a pinch.

For the nymph, the Basics Bead Head Nymph Assortment covers the smaller end — for a genuine drake nymph you want something larger and stouter, which is a good argument for tying your own: see the fly tying collection.

A big dun soaks up water fast. Loon Aquel for treating, Loon Dust for reviving. Browse all fly pattern assortments.

Where to fish it

The Henry's Fork is the most famous Green Drake water on earth and appears in our Idaho guide. The Colorado, Montana and Wyoming guides all cover drake water too.

Because the window is so narrow and moves with elevation, this is the hatch where local knowledge is worth the most money you'll spend all season. See our Certified Guides & Lodges, or build a trip around it through Book a Trip with Frontiers International Travel.

Fly Fishing Insider Podcast has a referral partnership with Frontiers International Travel. If you book after being introduced through us, we may receive compensation at no additional cost to you.

The bottom line

The Green Drake is worth rearranging your calendar for. It's short, it's weather-dependent, and it brings fish to the top that spend the rest of the year refusing to look up. Go heavy, strike slow, and follow it up the valley when it finishes where you started.

More hatches: the Pale Morning Dun, the Trico, the salmonfly, and the Blue Winged Olive.

Christian Bacasa, host of the Fly Fishing Insider Podcast