Lake Taneycomo

Entomology

Posted by Ryan Walker on August 15th, 2007
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As a beginning fly fisher, your main goal is to cast well enough to reach the fish with something close to the right fly. All of us started this way. As we progress in the sport, we hear terms like emerger, nymph, or dun. All of these terms are important to us, but what do they mean? The answers, for me at least, opened up a whole new world of fly fishing and tying possibilities and answered some nagging questions.

Entomology is the glue that binds this sport together. The main purpose of angling with a fly is to successfully mimic an actual insect in both look and behavior. Although there are a lot of patterns out there that mimic bait fish, crustaceans, and other food sources, insects are still the most predominantly imitated forms of trout food. But how much is to much? It is nice to know that the particular insect hatching at the moment is Psuedocloen Anoka, or the Tiny Blue Winged Olive, but without understanding that bugs life cycle, and how to mimic it, all the Latin in the world won’t catch fish feeding on them.

Let’s take some time and get acquainted with the four groups of insects most important to trout and their life cycles. These groups are: Mayflies, Caddisflies, Stoneflies, and Midges. We’ll start with the Mayfly.

Mayflies have 3 life cycles: egg, nymph, and adult. Of these cycles, the nymph and the adult (and their various stages) are of most importance to trout. Mayfly nymphs come in many varieties. The most common forms are; swimmers, clingers, and burrowers. Mayflies can spend from three months to a year or more in the nymphal form, making this stage the most readily available food source to trout. When the time is right, mayfly nymphs head for the surface. During this transition period, these bugs are extremely vulnerable and are easy prey for trout. Once at the surface, the nymph becomes trapped in the surface film and emerges using the tension of the film to extract itself from the nymphal shuck. At this point, we generally refer to these bugs as emergers. Once free of the shuck, the bugs wings unfold and begin to dry. At this stage the bug called the dun, or adult and is once again very vulnerable to trout. When the wings dry enough for flight, the Mayfly takes off to the streamside and undergoes it’s final transformation, shedding a skin and becoming a mating adult, or spinner. The spinner swarms above the water in a mating flight, drops to the water to deposit eggs, and very shortly after, dies, falling to the water, wings open or spent. This stage is readily taken by hungry trout and they will often ignore adult or nymph offerings of the same bug to dine lazily on this low cost meal.

Caddisflies are a true life cycle insect, meaning they complete four stages in their life: egg, larvae, pupae and adult. The larvae of the caddisfly is a worm like creature which exists in several forms. Net builders spin a silk-like net and live out their larval life in this structure. Case makers use the same silk-like secretion to fasten together small stones, sticks, leaves and other detritus from the stream floor to form a case to protect their soft bodies. Free living caddis larvae spend their time drifting with the current or clinging to rocks and such in the stream bed. All are predacious but are easy meals for trout when dislodged from their homes. The pupal form of the caddisfly wastes no time getting to the surface when emergence is near. Unlike mayflies, caddis squirt from their pupal shucks. This is often time when you will see trout leaping clear of the water. These babies are fast!! Caddisfly will also rest on the surface film to dry their wings and are vulnerable to trout at this time. After emergence, the adult caddis flies to the stream side and waits the mating period. Mating swarms of caddis can be dense and are a sight to behold. Literally thousands of bugs can be in the air at one time and can be seen afterward darting and dipping to the waters surface, depositing eggs. Several species of caddis will actually dive under the water to lay eggs. Easy marks for hungry trout.

Stoneflies are the giants of the aquatic insects trout feed on regularly. They have three life cycles; egg, nymph and adult and do not emerge in the water, rather crawl to the shore and emerge terrestrially. The nymph of the stonefly is by far the most important stage to trout ( in the Ozarks, anyway), often living two years in this stage. Some can get quite large, up to two inches or more, and are often highly predacious. These big bugs are poor swimmers, living their lives out as nymphs clinging to stones, leaves and other stream matter. When dis-lodged, the nymph often curls up, making it an easy target for waiting trout. When emergence is near, stonefly nymphs crawl along the bottom, heading for the bank and crawl to a nearby bush, tree or stone where they split their nymphal shuck and become adults.

Midges are the most often mis-understood insect we mimic for trout. These often tiny bugs are extremely prolific and supply a constant food source to trout. Midges have four life cycles: egg, larvae, pupae, and adult. There is really, in my opinion, no one stage past the egg that is more important to trout than another. Midge larvae are found both in the clinger and swimmer types. Clingers use a suction cup-like apparatus to cling to the bottom and are virtually helpless when dis-lodged. When the pupal stage is achieved, midges are left to drift freely with the current, often times attached to the bottom of the film by feather-like antennae. This drift- migration pattern is keyed in upon heavily by trout. There are at times thousands upon thousands of midge pupae drifting along, easy meals for hungry trout. Couple that with the fact that on many streams, tailwaters especially, this is the only reliable cold weather hatch, and you can see the importance this tiny insect holds for us as fly fishers. When emergence is at hand, midges squirt from the pupal shuck and their wings, then fly off to form swarms. These are a daily occurrence on the banks of Lake Taneycomo.

In this writing, I have been quite general in some terms and characteristics. I feel that understanding the insects life cycle, as opposed to knowing every minute detail of the bug, is as helpful in understanding why we fish the flies we do, and why trout react the way they do, as any information available. books of interest and help to the beginner include: Match the Hatch by Earnest G. Schwiebert, Naturals by Gary Borger, Guide to Aquatic Trout Foods by Dave Whitlock, and Aquatic Insects, An Orvis Streamside Guide by Dick Pobst.

The next part of this series will cover fly selection for each stage and why some patterns will effectively imitate several insects at once.

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