Hatches and what trout eat

Hook sizes 16 to 22, most often 18 to 20

Blue-Wing Olive

The small olive mayfly that hatches on cold grey days from autumn to spring, when almost nothing else does. Sizes 16 to 22.

Hook sizes 14 to 18, most often 16

Pale Morning Dun

The defining western summer mayfly. Pale yellow bodies, midday hatches that run for weeks, and trout that get very fussy about them.

Hook sizes 8 to 12

Green Drake

The hatch anglers book holidays around. Big mayflies, a week or two of it, and the largest trout in the river feeding on the surface.

Hook sizes 10 to 14

March Brown

A big mottled mayfly that trickles out over hours rather than erupting, keeping trout looking up all afternoon. May and June, not March.

Hook sizes 20 to 26

Trico

Tiny black-and-white mayflies that swarm at dawn in late summer. The spinner fall looks like smoke and the fishing is the fussiest of the year.

Hook sizes 12 to 20, most often 14 to 16

Caddisfly

The most abundant trout food in moving water after midges. Tent-winged adults, cased larvae, and a rising pupa most anglers never fish.

Hook sizes 4 to 8

Salmonfly

Two-inch orange stoneflies on western rivers in June. The hatch climbs the river a few miles a day and the biggest trout eat on top.

Hook sizes 6 to 12

Golden Stone

The hatch that follows the salmonflies and outlasts them by weeks. Smaller, more abundant, and more useful to plan a trip around.

Hook sizes 12 to 16

Yellow Sally

A small bright yellow stonefly of summer freestone water. Less famous than the giants, easier to fish, and taken without much inspection.

Hook sizes 18 to 26, and smaller on hard-fished tailwaters

Midge

Tiny, year-round, and the reason winter fishing works at all. On tailwaters they are the most important trout food there is.

Hook sizes 6 to 12

Grasshopper

Big, clumsy and helpless in the water. July to September on grassy banks, best in the wind, and the most forgiving dry-fly fishing there is.

Hook sizes 14 to 20

Flying Ant

The fly that saves blank afternoons. Trout eat ants out of all proportion to their size, and a mating flight can switch a dead river on.

Hook sizes 12 to 18

Beetle

The most under-used fly in a summer box. No hatch required, sinks like the real thing, and reliably takes fish that refuse everything else.

Hook sizes 12 to 18

Scud and Sowbug

They never hatch, so trout eat them every day. On weedy tailwaters and spring creeks they can be most of a trout's diet.

Hook sizes 2 to 10, and larger on big western rivers

Baitfish and Sculpin

The largest regular meal a trout gets, and the reason streamers exist. Fewer fish, bigger fish, best in coloured water and autumn.

Hook sizes 2 to 6, tied on deer hair or foam

Mouse

A night fishery for the biggest brown trout in the river. Very few takes, and the takes are from fish nothing else reaches.

Hook sizes 8 to 16, or a bead of 6 to 10 millimetres

Egg

Not a hatch but a food supply. During a spawning run an egg pattern is the most effective fly in the country.

Hook sizes 8 to 14

Aquatic Worm

Real, abundant and available every day of the year. The fly to reach for when the river comes up or colours after rain.