Trout Stream Insects, Natural Mayfly Nymph, Artificial Mayfly Nymph

by Fly Fisherman

Trout Stream Insects
From the standpoint of imitating the trout’s most important food, wet flies lead all other artificials. This is because aquatic insects in their underwater, or non-flying, stages constitute by far the largest portions of the food of all stream trout. This is true for Brook trout, Brown trout, Rainbows, Cutthroats and Dolly Vardens.

Natural Mayfly Nymph    Artificial Mayfly Nymph
Any thoughtful angler can see the importance of knowing something about these aquatic or water insects that are the chief food of trout. There are five main groups: mayflies, caddisflies, stoneflies, alderflies and true-flies.
There are times when certain conditions make it almost impossible to catch trout; but it is always possible in a trout stream to catch stream insects. During the noon lunch period, on a hot day when the trout aren’t rising well, just pick up some stones out of a riffle and look at the under side of the stones.
You will find the surface of the rock covered with nymphs, larvae and pupae of the various aquatic insects. Notice the ingenious little cases or houses made of tiny pebbles or pieces of wood that the eaddisfly larvae and pupae live in. Maybe you will see the clever little nets that these underwater forms of caddisflies weave to catch the miscroscopic plant food they live on. You will see the nymphs of mayflies that are so often imitated in wet flies. You will probably see some stonefly nymphs with brilliant black and yellow color patterns on their backs and heads. Probably you’ll find hellgramites and dobson fly larvae, too.

All observant fishermen know that the young of aquatic insects are very different from adults. The immature underwater forms of mayflies, stoneflies and dragon flies are called nymphs. Except that they have no wings, nymphs are much like adults. The stages of development of these insects are from egg to nymph to adult water insects.
The underwater, immature stages of caddisflies, alderflies, dobsons and true-flies (two winged flies such as midges and black flies) are called larvae. They are not so much like their adults. They develop through four distinct stages: egg, larva, pupa and adult. The pupal stage is spent in sort of retirement in some shelter made by the larva. During this time the insect develops into the adult form.
Trout feed on the nymphs and larvae of these aquatic insects, both on the bottom of trout streams and when they are coming up through the water to emerge as adult winged insects. Some varieties of nymphs and larvae hatch into adults on the surface of die water and fly off. Others crawl out on the banks of the stream or to rocks or sticks and hatch into the adult winged insects there.

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