Certain aquatic insects make up the major portion of a fish diet. The four main insect orders that emerge from our streams and lakes (in order of importance) are mayflies (Ephemeroptera), caddisflies (Trichoptera), midges (Diptera) and stoneflies (Plecoptera).

To be an effective hatch-matcher you must be able to quickly differentiate between adult mayflies, caddisflies, midges, stoneflies and all the immature stages of each. Many hatches and most spinner falls do not last very long, so you don't have time to try four or five patterns. Instead, you'll need to choose the right fly at the right time; only then will you be able to hook your share of fish.

It's easier than you think. Just remember to match the hatch.

Types of Flies

Mayflies

The mayfly (Ephemeroptera) is the most important order of trout-stream insects. All mayflies have two large, upright wings; two or three tails; and most have two very small hind wings. Mayflies look like little sailboats floating in the current and are the only trout-stream insects with upright wings. The life cycle is: egg, nymph, dun (subimago), spinner (imago).

The Nymph

Mayfly eggs hatch into an underwater form called a nymph, which usually lasts about a year but may last two months to two years or more, depending on the species. Nymphs range in size from 3mm to 36mm or more and have three tails (rarely two) and gills emanating from the sides of the middle segments of the abdomen.

Nymphs grow from a very small size through progressively larger stages; each stage, called an instar, is accompanied by a molt. Nymphs vary greatly in shape, depending on the ecosystem they have become adapted to, such as fast or slow water. Most nymphs are dirty tan to brown in color with a lighter underside, but they can vary from cream to olive to black.

The Emergence

When the nymph is fully grown, it swims to the surface and changes into a winged fly called a dun (subimago) by splitting its nymphal skin and emerging from it. The dun rests on the surface, drying its wings, and then flies away to nearby trees or meadows. This entire procedure is called "the hatch." At this time the nymphs and the duns are extremely vulnerable.

Before and during the hatch, a standard fur-bodied type of mayfly nymph of the correct size and color fished wet is a good imitation to use. During the hatch, a mayfly-dun imitation such as a Sidewinder No-hackle Dun is my personal choice.

A standard hackle pattern can be fairly effective if tied sparsely. The fur body is what really floats both the No-hackle Dun and the sparse standard pattern.

One of the most deadly patterns of all during an emergence is the floating nymph. Over the years, I've found that trout often eat two or three nymphs for each floating dun. I believe trout prefer the floating nymphs because they have more time to capture the nymph. The dun, after all, can fly away at any time, but the nymph cannot.

The Spinner Fall

After the dun has dried its wings and flown to the trees, it rests for a period of a few hours to a few days and then undergoes a final molt into a spinner.

The dun is a drab insect with dull, opaque wings, and tails approximately equal in length to the body. The spinner is, by contrast, bright and shiny, with long tails (twice as long as the body), and clear transparent wings. The spinners return to the river, mate in a swarm (usually over riffles), and fall spent into the stream after egg-laying. During the spinner fall the correct imitation is a one-half-spent or full-spent mayfly spinner imitation. My personal choice is a Hen Spinner in the correct size and shape.

Spinner falls occur more often in the evening or at dark but can also happen during the morning hours, depending again upon the species and, of course, the weather. As a general rule, early-season mayflies (March to May) tend to be dark in color: dark gray wings and dark brown or olive bodies. Later, as the lighter yellows and greens appear, the prevalent insects are lighter in color, most likely to blend in with the background and escape their many predators. The wings become pale gray and the bodies yellow and pale buff or olive. Then in September and October, emerging flies are darker again. As the autumn leaves turn dark, so do the insects.

Caddisflies

Caddisfiles (Trichoptera) are also very important insects, and in some locations they are even more numerous than mayflies. Caddisflies can easily be distinguished by their four wings of nearly equal length, which are covered with tiny hairs and, when at rest, are carried in an inverted V or tent over the back. Caddisflies are usually medium to small in size (#14 to #24) and have no tails. There are more than 1,000 known species on this continent.

Caddis Lifecycle

The life cycle of a caddis differs from the mayfly and follows this order: egg, larva, pupa, adult. The eggs are deposited in or near the water, eventually hatching into a worm, which may or may not build a case, depending on the species. Two large groups of caddis larvae exist. One group builds a case or house (evidently for protection and camouflage) in which the larva lives. These cases may be constructed of practically any material such as twigs, stones, and bits of leaf or bark.

The other caddis are free-living, meaning they range about the bottom of the stream without cases. When matured, the larva makes a cocoon (much like a caterpillar) in which it changes into a pupa. When the pupa is fully developed, it cuts its way out of the cocoon and migrates to the surface. Some species crawl out of the water to emerge, and some drift in the film until the pupal skin is broken and the adult flies away.

The adult caddis are able to live much longer than mayflies, because they can absorb water. Most caddisfly species mate at rest, so the females are the ones taken by fish at egg-laying time. The caddis eggs are deposited on the water, on vegetation overhanging the water, or under water by diving females.

Caddis Hatch

During a caddis hatch three imitations are effective. Due to the drifting of the pupa in the film before emergence, a pupal imitation fished wet is often deadly. The stillborn adult, which is a pattern tied to imitate a fly stuck halfway out of the shuck on the surface, is in my experience the most deadly of all the patterns during an emergence. The dry Henryville Special is good at hatch time and during the egg-laying flight. A spent caddis is effective at the end of the fall of spent adults.

Of course, you must match the size and color of the natural with the artificial. As with all flies, a specimen must be captured and examined in the hand. Adult caddisflies are jumpy and wary, so are difficult to capture. Often an aquarium net is required. Caddisflies are attracted to bright lights, however, and during the evening your car lights can be a good collecting spot. With so many caddisfly species existing, most anglers do not bother to identify this order precisely as to species. It is enough to be aware of the five main colors - tan, gray, olive, cream, dark brown - and to have reasonable imitations in sizes 14 to 20.

Midges

Midges (Diptera) have only two short wings (shorter than the body), which lie flat along the top of the body, usually slightly to the side in a V, and they have no tails. Most midges are small, size 22 to 28 or smaller. The life cycle is egg, larva, pupa, adult. At hatch time the pupa ascends to the surface where it drifts for a time; the winged insect then emerges and flies away.

During the hatch, a pupa or stillborn artificial midge is usually effective; a hackled adult type can be used later during the emergence or at the egg-laying flight.

Midge Sizes

These flies are especially important to trout in slower-moving water such as spring creeks and limestone streams. Some lake-dwelling midges are fairly large. They are rarely of much importance in faster currents. This is a very large and diverse group; midges can be almost any color, but black and olive are common. When trout are feeding on midges, they can be extremely selective. Exact size in the artificial is often critical. An error of a single size (#20 instead of #22) can mean a discrepancy of more than 30 percent, and almost always this is perceived by the critical eye of a trout. To be effective, close imitations of midges are necessary.

Midge fishing is often considered the ultimate challenge in fly fishing, because the imitations are very tiny and fly leaders must, therefore, be extremely long and fine. Leaders of 10 to 14 feet with tippets of 6X, 7X, or 8X are the most effective sizes. Light fly rods with fine tips are required to protect the fine tippets when striking and fighting a hefty fish. Of course, very small mayflies (Tricorythodes, Baetis, Pseudoeloeon), caddis, and terrestrials require the same light tackle; and while they are not technically midges, they are generally lumped together under the term midge fishing.

Stoneflies

This small order of flies is of very little importance in slow waters, yet in turbulent, rocky streams, such as the Madison and the Big Hole in Montana, stoneflies (Plecoptera) provide the largest flies and the most spectacular fishing of the season. In certain Oregon streams, stoneflies are the second most important fish food. Stoneflies vary in size from very large to very small (#2 to #20). Adult stoneflies have four long wings, which are hard, shiny, heavily veined, and held flat over the back when at rest.

Stonefly Life Cycle

The life cycle is egg, nymph, adult. The generally flatish nymphs are readily distinguished from mayfly nymphs since they have only two short tails, rather long antennae, no gills on the abdomen, and two equal wing cases. When the nymph is mature, most species (but not all) crawl to land and emerge. They mate at rest and return to the water a few days to a few weeks later to lay their eggs.

Stonefly Emergence

The emergence is important only in those species that emerge in water, and they are best imitated by a combination latex-and-fur stonefly nymph or a down-hair-wing dry imitation. The egg-layers are well imitated by an adult stonefly artificial with a lot of hackle to simulate moving wings. Many of the medium and small stoneflies are yellow with a few showing olive, tan and dark brown. Usually the underside of the nymph is much lighter than the top.

Selecting an Artificial

How do you translate this knowledge into a fishing situation? Imagine you are in the middle of a pool with fish rising all around, flies buzzing in the air and drifting on the currents. How do you select the correct imitation? How do you pick an artificial at the right time that will take fish when they are feeding?

Insect Order

First, determine what type or order of insect is on the water. This is done by capturing one and examining it closely in the hand, preferably with an 8X or a l0X magnifying glass. If the flies are on the water, a simple tropical-fish aquarium net can be dipped onto the flow, and the current will carry the specimen into the net. If the fly is in the air, a simple net can be fixed to a stick and used like a butterfly net.

Determine What Fish are Eating

If fish are observed feeding underwater, two methods can be used to discover what they are feeding on. The best way is to catch a fish (usually one dummy can be taken using an attractor, such as a Coachman fished wet) and pump its stomach with a stomach pump. You then have proof positive of the fish's preference. If landing a fish is impossible, a simple wire seine can be held in the current while gravel and vegetation is dislodged upstream. Whatever is present will be washed into the seine and can be examined closely.

Once the specimen is in hand, the order and stage is determined (e.g., wet fly, nymph, dun, or spinner). Then select an artificial of the correct size, shape, coloration and type from the fly box, and you should be good to go.

This whole process takes place in the heat of battle, however, and a certain calm deduction is required. Most people get so excited by splashing fish that they take a wild guess as to the correct pattern and immediately begin to flail the water. They normally end up exhausted, frustrated and fishless.

To be successful you must remain calm, patiently obtain a specimen, and know a mayfly has upright wings, a caddis has tent-shaped wings, a stonefly has flat wings over the body, and a midge has flat, V-shaped wings (flat but to the side of the body); and you must know which artificial type works when each natural is on the water. If you are thoroughly familiar with these facts, you will be light-years ahead of most fly fishers and much more effective.

The Multiple Hatch

I have just described a simple hatch where only one or two types of insects are hatching at a time. Any observant fly fisher with a little knowledge of practical entomology should be able to choose his pattern and do well during such a hatch.

A much more difficult experience occurs during a multiple hatch. How do you select the right fly? This is a difficult problem even for veteran anglers. The answer is never simple. Experience, knowledge and close observation are required. A few bits of information should be of help.

Size of Food

First, trout usually feed on the insect present in the greatest numbers. Quite often a small fly will be present in company with a large fly but in much greater number; the fish will feed on the smaller fly exclusively, though the inexperienced fly fisherman usually tries the larger fly first. Try to decide which natural is most numerous. If a suitable imitation does not work within five minutes, look again and try another. Do not keep casting uselessly with the same pattern.

Riseforms

Next, try to identify the riseform and relate that to a fly type. Trout will rise very quietly and deliberately to insect forms that are smaller and cannot escape, such as medium to small mayfly spinners. The larger and more escape-prone the insect, the more hurried and splashy the rise. So if you observe that #12 Green Drake duns and #18 Baetis spinners are both on the water, and the riseforms are quiet dimples, the obvious choice would be #18 Hen Spinner in the correct color. Conversely, a violent riseform would indicate a #12 Sidewinder Dun to imitate the Green Drake.

At times when no hatch is in progress, and especially just before a hatch, fish will feed on the bottom as the immature insect forms become active prior to hatching. Seine the river and discover which nymphs are the most numerous and more mature (these will have the darkest wing pads). Often, you will find that the fish have a preference for smaller but more numerous forms over the larger but less prevalent species.

These multiple hatches can be mystifying, so don't be discouraged by a few failures. One of the most pleasing aspects of fly fishing is its complexity. I would soon tire of constant success, and multiple hatches certainly ensure against that. However, the practical entomologist will have a fighting chance at a solution to the problem.

Other Food Items

Trout and other freshwater gamefish feed on many other food items besides the four major orders. Although these other orders are normally of lesser importance, when they are numerous, fish will feed on them selectively, so a few representative imitations should be carried for the other aquatic, semi-aquatic or terrestrial forms, such as dragonflies and damselflies (order Odonata), grasshoppers and crickets (order Orthoptera), leafhoppers, true bugs (order Hemiptera), spongilla flies (order Neuroptera), Dobsonflies, fish flies, alderflies (order Megaloptera), aquatic moths (order Lepidoptera), beetles (order Coleoptera), true flies (order Diptera), and aquatic wasps (order Hymenoptera).

As you can see, this is a diverse group of insects available for fish to feed on, and they have adapted to every type of ecosystem imaginable, from lotic (running waters) to lentic (standing waters) and everything in between. Some aquatic insects can survive and flourish in streams that periodically dry up completely.

In addition to aquatic insects, some crustaceans are heavily fed upon by trout and bass. Thus wet flies, fished deep to represent scuds, sowbugs, shrimp, crayfish and other similar aquatic creatures, are often very effective when no surface activity is apparent.

Terrestrials

If all those weren't enough for the fly fisher to imitate, quite often terrestrial insects get blown onto the water's surface. These are not normally as important as the aquatic insects; but at times, when large numbers appear on the surface, they can provide some very exciting fishing. Grasshoppers provide a large juicy meal, and large fish will be on the lookout for them during late July, August and September. Trout seem to relish ants, and in the fall, large flights of winged ants often appear in numbers. At these times the fish are very selective and antlike body imitations are essential.

Other terrestrial forms such as green oak worms, jassids, large beetles and spiders when they are in season are also important. Most fly fishing with terrestrials is done with dry flies.

Original article written by Carl Richards (adapted for this use).
Courtesy of Fly Fisherman Magazine