My studies of how trout feed on emerging pupae and my observations of the naturals also shed considerable doubt on the "rocket" concept of a caddisfly hatch. At least for those swimming emergers observed, including six important trout-stream families, my studies show that the ascent has definite periods of hesitation. It is the insect during these periods of hesitation that fly fishermen must imitate with their flies. They have to know where the pupae will pause and struggle before they can begin to fish a caddis fly hatch successfully.

What is the secret? Efficiency. The principle is simple; the actual attainment of it is not. Many anglers flail randomly, their fly occasionally crossing those areas where vulnerable insects concentrate, catching fish only when their fly is in a prime area. The expert, however, changes his tactics as the prime areas change, and keeps his fly for as long as possible in the productive zone.

The key to anticipating, or "ambushing," a caddis fly hatch requires breaking the common notion of what it is. Too many fishermen only recognize the peak of the action, the frantic surface feeding coinciding with the heaviest concentration of insects on or under the surface film, but these fishermen miss out on fishing before or after the peak — fishing that is sometimes even better.

The first time an angler encounters heavy insect activity, he cannot anticipate it. It is a blind situation — he is unprepared for the ensuing feeding spree. He fumbles in his fly box for some kind of a matching fly and casts to the rising trout with various techniques. If he fails to find the right combination with his hasty attempts, he probably ends up frustrated and fishless.

Even a regular on a stream, lacking an understanding of entomology, cannot fully master such a situation. He might have enough experience with a particular insect to use proper flies and tactics during the main hatch, his methods worked out by past trial and error, but he can still only take advantage of the activity he sees, the hour or so of actual surface feeding. He cannot take advantage of the subsurface activity he does not see.

The fly fisherman who understands the typical life cycle of stream caddisflies, however, knows the vulnerable subsurface stages. He discovers where, when, and how the concentrations occur during an emergence, which allows him to anticipate and prepare for the appearance of the insect. This knowledge also allows him to take full advantage of the predictable daily feeding schedule of the trout. Such an angler is not a member of a scientific cult, but simply a fly fisherman who is prepared to match his tactics and flies to the changing concentrations of insects. There are three areas in which caddisflies concentrate during a hatch.

The First Area of Concentration

Usually, hours before the main hatch, some caddisflies begin popping out. The first of these random emergers often reaches the surface safely because trout are not conditioned to the occurrence, but soon fish take notice of the hatch. Even when they do start feeding, however, the trout seldom rise to grab a natural from the surface.

The emerging insects, fully formed adults inside thin and flexible pupal skins, cut their way free of the cocoon. Most species do not begin to rise immediately, though. Before they can start swimming they must generate air bubbles inside the transparent pupal skin. They drift momentarily with the bottom currents, enough of them carried along to create a concentration of helpless prey.

This is the first hesitation in the emergence of caddis flies; and preliminary to the main hatch the fish seem content to stay on the bottom, plucking the freely drifting pupae. Trout can feed for hours on these forms without breaking the surface or chasing an active insect.

A stomach sample from a trout caught just before the main caddisfly hatch will often be jammed with hundreds of emergents. These stomach contents are usually a complete surprise to the angler, but they demonstrate the extent and intensity of this unseen bottom feeding.

The tactic for matching this early hesitation of emerging caddisflies is seldom associated with the pupa. All kinds of techniques are recommended for a hatch, usually lifts, swings, or retrieves, which may be suitable at a different time, but when trout are keyed to the inert insect near the bottom the way to fish an imitation is dead drift with the standard upstream or across-stream nymph presentation. An occasional tightening of the line, kicking the fly into brief motion, followed quickly by a mend that drops it back into a drift can be added to the basic method.

Imagine, then, being able to fish successfully for hours before the main hatch and the visible surface feeding of trout. It is not difficult to capitalize on this opportunity if the angler will only take the time to learn the approximate emergence dates of the important caddisflies in the streams he fishes.

The Second Area of Concentration

Once out of the silk-lined, stone or vegetable cocoon, drifting freely in the stream, the swimming caddisfly emergent begins inflating its surrounding skin with gas bubbles and beating with hair-fringed legs, both of these actions lifting the insect up through the water. At the surface the adult hesitates, pushing against the underside of the meniscus (surface film) and struggling to shed the pupal skin.

Most caddisflies do not ride on top of the water for great distances, but they do drift, some longer than others, hanging half in and half out of the surface film and invisible to all but the most careful observers. The emergent pulls out of the pupal skin with a series of wiggling motions. Once free, it takes off after a preliminary hop or two.

Ken Thompson, an aquatic biologist, puts the role of the surface film during emergence into perspective, "The meniscus, or surface film, poses an unbelievable barrier to insects trying to pass through it, either from above or from below. It is the result of the molecular bonding of water molecules, which have areas of positive and negative charge. Under the surface the charges are equal, but at the surface the molecules are 'unsatisfied' and under tension.

"A great amount of physical energy is required for an insect to break through the resultant surface tension (meniscus). An example, in human terms, would be the amount of energy needed for a full-grown person to escape if he were covered with three feet of dirt. Aquatic insects have evolved (through necessity) various ways to overcome this barrier. Swimming emergents swim to the surface and push against it. When the top part of the pupal thorax protrudes through the surface and splits open, a meniscus forms around it, thus creating an escape hole in the surface. As the pupal skin (nymphal skin in the case of mayflies and stoneflies) splits open, it is actually aided by the force of the surrounding meniscus, and the adult insect passes through the hole, never even touching the water. Once an insect is on the surface, its structural hairs and water resistant skin help to keep it floating high until it flies away."

During a major hatch this second period of hesitation creates a tremendous supply of helpless prey in the surface film. This is the stage that triggers the visible feeding. Trout break the surface with porpoising rolls, taking an insect and turning down. Occasionally a trout jumps into the air, its momentum carrying it out of the water.

The fish usually switch over very quickly, abandoning deep feeding, once the main hatch erupts because pupae hesitate and drift longer at the surface than they do near the bottom. The concentration of insects becomes much heavier in the meniscus, and once this happens the upper level is where fish can feed most efficiently.

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