How to Match the Hatch

Choosing the correct fly at the height of an insect hatch, when the trout are selective, is the most complicated, exasperating, and, when you find the right fly, satisfying experience in fly-fishing. The challenge involves not only what species of insect the fish are feeding on, but also the stage—is it an emerging adult, a drifting nymph, or a spent egg-laying adult?

The classic case of dry-fly fishing is when you arrive at a stream or lake to find the trout rising and the water covered with hatching mayflies. You pluck a fly from the air or the surface of the water, lay it on the lid of your fly box, and choose the fly in your box that matches it in size, shape, and color. Then you proceed to catch lots of fish.

It’s seldom that easy. Faults in your presentation may tip the fish off to the fact that your fly isn’t real. (We’ll cover those problems in a future post.) You can have what is called a masking hatch, usually a large fly that is hatching at the same time as a smaller, less obvious fly. But the trout may prefer the smaller fly, because it’s more abundant or easier to capture.

Every trout-stream insect has a Latin or scientific name, and you may hear other fly fishermen using these names. Latin names eliminate confusion about insect hatches between different areas of the country—an Ephemerella subvaria is called a Hendrickson in some parts of the country and a Whirling Blue Dun in others. It isn’t necessary to know Latin names to catch fish. It isn’t even necessary to know the names of the flies in your box until it’s time to reorder. As long as you can match the natural to its imitation, you’ll be a successful fly fisherman.

The secret is observation. Before you start flailing the water with your favorite dry fly, watch the fish that are rising. Find one that’s rising steadily, and keep your eyes glued to the spot. Did he take the big cream mayfly or the little gray one? Perhaps he keeps rising but the flies that float over his head remain untouched. Are there bubbles after a take? If there are none, he’s probably taking the emerging nymphs just under the surface.

Subsurface Clues

Here is what usually happens during a hatch: from a couple of days to an hour before the flies hatch, the nymphs or pupae become restless and drift in the current or scamper around on the aquatic vegetation in a lake. Trout pick off these nymphs, but we have no clues unless there has been a hatch for the past few days or your fishing diary or a book on trout-stream insects tells you a hatch is due on this date.

Because the trout are preoccupied with underwater food, they’ll probably ignore floating flies, so you’ll want to try a wet fly or nymph. Turn over a few rocks on the stream bottom. The flies that are due to emerge will be more abundant on rocks at the stream’s edge, and their wing cases will be almost black. Choose a nymph from your fly box that matches them as closely as possible.

At the beginning of the hatch, you’ll see a few flies in the air and a few on the water. Rises will probably be scattered and erratic. What you’re most likely seeing is fish feeding just under the surface; occasionally they’ll misjudge and break the surface or cause a swirl. This is the time for a wet fly fished just under the surface, an emerger pattern, or a floating nymph.

Trout feeding just under the surface can be exasperating. You see a fish rise, toss your dry fly to him, he splashes at it, the water bulges under it—and you strike and come away empty. This is called a refusal. It may occur because your fly is the wrong size, but often occurs because the fish doesn’t want a fly that is floating that high. He puts on the brakes at the last second, but his momentum causes him to break the surface. You might think that he missed your fly or you didn’t strike quickly enough. Don’t believe it. An adult trout seldom misses his target, and when he wants a dry fly it’s tough to take it away from him.

Another clue to subsurface feeding is a splashy rise from which erupts an adult fly that flies away. The fish has chased a nymph off the bottom but hasn’t been quick enough. This is a very common sight during caddisfly emergence. If you see little mothlike flies popping out of rise forms, put away your dry flies and fish a caddis-pupa imitation just below the surface.

During hatches of many mayflies and caddisflies, the trout take the emerging flies throughout the hatch and bother little with the adult flies resting on the water’s surface. You may catch a few on dry flies, especially if your fly isn’t floating too well, but you would have been more successful using an emerger or wet-fly pattern. In most hatches, however, there will come a time when there will be enough flies on the surface to tempt the trout to take the adult insects—and your high-floating dry flies. Rises will be deliberate, rhythmic, and you’ll see bubbles.

Splashy rises indicate fish taking insects that are fluttering on the water; as I’ve said before, this usually indicates a caddisfly hatch. A downwing dry fly of the correct size and color should work. Rises to adult mayflies are usually more sedate, unless the mayflies are very large or the wind is blowing them across the surface like tiny sailboats.

It’s usually not good enough to gauge the size and color of a hatching fly by observing it in the air or on the water. Flies look larger in the air, and color in a moving insect can be deceiving. Catch a sample to be sure that your match is correct.

At the height of a hatch you may see fish taking adult flies, know you’re fishing with the right size and color, and know that your presentation is OK—and still get refusals. This is the time to switch from a standard hackled dry to a thorax fly, no-hackle, or comparadun, something with a slightly cleaner silhouette. The change to a different pattern of the same size and color will often fool a difficult surfacefeeding trout.

There are thousands of different dry-fly patterns. Most aquatic insects are gray, cream, brown, or olive, and if you have one pattern in each of these colors in sizes 10 through 24 you’ll be able to match almost any insect hatch in the world. This approach is much less confusing than trying to fill your fly box with hundreds of different patterns, many of them redundant when it comes to imitating a particular insect.

Excerpted from The Orvis Fly-Fishing Guide, by Tom Rosenbauer.