What Trout Eat
Trout eat a host of aquatic insects, terrestrial insects, other fish, crustaceans, leeches, worms, and other foods. The food items that are most important to trout and fly fishers are the aquatic insects that spend most of their life cycles underwater in rivers, streams, and stillwaters. They grow to maturity underwater and transform to flying air-breathing adults that mate in the air above our favorite waters.This movement from the water to the air exposes the insects to predators such as trout and birds, and often causes a feeding frenzy. This event is called a “hatch” and is the situation all fly fishers search and hope for onstream.During a hatch, when insects emerge en masse, trout become so focused on this one food item that they will often eat nothing else. This is called selective feeding.“Matching the hatch”--another common term you’ll hear in fly-fishing circles--is the act of choosing the right fly and presenting it in the correct manner to fool selectively feeding trout. To do this you must be able to identify the insect, be familiar with its behavior, size, shape, and to a certain extent color, so it’s important to have a working knowledge of the most important types of insects mayflies (Ephemeroptera), caddisflies (Trichoptera), midges (Diptera), and stoneflies (Plecoptera).Don’t worry, you don’t need to know the Latin names of each type of insect but it may help later on when you learn to discern one type of mayfly from another and want to accurately describe the insect to fellow fly fishers. A good text on identification is Hatches II by Al Caucci and Bob Nastasi, but a more up-to-date guide may be www.troutnut.com, which would be better named as www.bugnut.com because the web site is almost entirely devoted to current freshwater insect identification and information. During your journey to becoming an expert fly fisher, you should make a habit of picking up rocks from the river bed and examining streamside bushes to identify the important insects in that stream. Some fly fishers eventually evolve into amateur entomologists and take and keep samples of the insects they see onstream with the idea of tying flies that more accurately imitate them.MayfliesWhen fly fishers think of a hatch, they usually think of a mayfly hatch because mayflies create the most elegant fishing situations, are important foods in all trout waters, and have been studied and written about by fly fishers for hundreds of years.Mayflies begin life as an egg, and hatch into an aquatic stage known as a nymph. Nymphs usually live about a year but may last two years or more, or just a few months, depending on the species. Some mayfly species have two broods per year, making them important in the spring and again in the fall when the next generation matures.Mayfly nymphs range in size from 4mm to 40mm and most often have three tails (sometimes two). Some mayfly nymphs are burrowers, others have adapted to cling to rocks in fast water, so each nymph species has a different body shape and design. Most are dark on top (mottled brown, tan, or dark olive) with a lighter-colored underside.There are sophisticated fly patterns designed to accurately imitate specific mayfly nymph species on specific waters, but in most instances, general-purpose patterns such as Hare’s-ear or Pheasant-tail nymphs in sizes 8 through 18 are fair imitations of nearly all important mayfly nymphs.When a mayfly nymph rises toward the surface and splits its shuck, the insect that emerges is called a dun (technically a subimago or pre-adult). They have two large, upright wings, two or three tails, and most have two very small hind wings. The wings are opaque and their bodies are often drab-colored. Duns are the mayflies that ride the water’s surface in an upright position while their wings dry before taking flight. It’s a cliché, but fly fishers often say they look like miniature sailboats. When duns are on the water, you are in the hatch situation fly fishers live for, and it’s time to fish with dry flies, which float on the surface of the water.Hopefully you’ll find trout rising to the surface to eat these mayflies, and if you can get the right fly into the right place, you’ll watch the trout rise to the surface and close its mouth around your fly.Your local fly shop has bins full of dry flies to imitate the dun stage of each local mayfly species, but for most trout you don’t need an exact imitation. As long as you have a fly that is about the right size and shape, and you deliver it accurately, you will catch fish.A Parachute Adams is a good fly to imitate all mayfly duns. It has the right profile, the white wing post is easy for you to see on the water, and the gray body fools many fish. You’ll need them in sizes 8 through 20 depending on the size of mayflies in your local waters.After they hatch, mayfly duns fly to streamside vegetation where they molt or shed their skins and enter the adult or imago phase fly fishers call “spinners.” The change from dun to spinner often results in a different body color, and spinner tails are longer than dun tails. The most noticeable difference is that the wings of mayfly duns are opaque or cloudy. Spinner wings are usually clear.A short time after molting into spinners--usually within 24 hours--the mayflies fly back to the water and gather in large swarms over riffle areas, where they mate. This most often happens late in the evening or early in the morning.
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