In plain old English, we’re going to cover the basics of 95% of the bugs you’re likely to encounter on any given trout fishing outing.

Caddis

You’ll encounter caddis in streams and lakes all over North America. There are close to a thousand different species of these bugs! The caddis life cycle looks like this:

• egg
• larva
• pupa
• adult

There are 2 main groups of caddis larvae: “case-building” and “free-swimming.” A case-building larva builds a case around itself with small grains of sand and sticks, while a free-swimming larva ranges about the bottom of the stream without a case. Either way, you can often find caddis larvae clinging to rocks. A few weeks before becoming an adult, a caddis larva seals itself in a cocoon, in which it begins changing into a “pupa.” When the pupa is fully developed, it gnaws its way out of the cocoon and heads for the surface. Which flies represent these immature caddis best? To imitate the larvae, you can’t go wrong with patterns like the Peeking Caddis and the Cased Caddis, as well as the aptly named Caddis Larva. For pupal imitations, it’s tough to go wrong with the Soft Hackle Caddis, Zug Bug or Sparkle Pupa.

Learning What Trout Eat

Learn what trout eat and what lives on the river bottom. This clip will give you a good overview of what flies to use.

As the caddis pupa rises to the surface, it sheds its pupal husk, and the adult caddis struggles out. Depending on the species, adult caddisflies can be anywhere from 1/8″ to 2″ long. Caddisflies have four wings that extend past the body. At rest, these wings are folded tentlike over the body in an inverted V-shape. Caddisflies have two feelers that extend past the body, long legs and no tails. In flight, caddisflies look a lot like moths; up close, however, there’s no mistaking the two. Dry flies that do a nice job of replicating the adult caddisfly include the Elk Hair Caddis, Henryville Special and CDC Caddis.

Mayfly

Like caddis, the mayfly is an extremely important trout-water insect. Mayflies go through a metamorphosis that looks like this:

• egg
• nymph
• adult—dun
• adult—spinner

Mayfly nymphs are found in both lakes and streams, usually hiding under rocks or vegetation. There are two fly patterns that have universal appeal as mayfly nymph imitations: the Pheasant Tail and the Gold Ribbed Hare’s Ear.

Once the nymph fully develops, it swims to the surface and splits its nymphal skin, becoming a winged adult called a “dun.” The dun sits in the surface film and waits for its wings to dry so that it can fly to the shore. Floating on the water, the dun looks like a tiny sailboat, with its wings folded up over its back like a sail. (Mayflies are the only trout-stream insects with upright wings.) As soon as it’s able, the dun flies to the shore. A short time later, it molts and becomes a “spinner” and is now ready to reproduce. Popular adult mayfly imitations include the Parachute Adams, Pale Morning Dun, March Brown, Ginger Quill and Blue Wing Olive.

Stonefly

Stoneflies require a lot of oxygen to live, so they’re almost always found in rocky, turbulent streams and rivers. The life cycle of a stonefly is a simple one:

• egg
• nymph
• adult

Stonefly nymphs are free-swimming insects that have 2 tails and 2 long feelers. Good stonefly nymph patterns include the Montana Stone, the Bitch Creek and the Brown Stonefly. If you’re caught without one of these flies, don’t hesitate to try the versatile Woolly Bugger.

Once the stonefly nymph matures, it crawls to land and emerges as an adult. The adult stonefly looks like the nymph, except that it has wings. At rest, these wings are folded flat over its back. The biggest stonefly is almost 3″ long, and the first time one lands on you, it’ll scare you half to death! Not to worry, however – they don’t bite or sting. The Kaufmann Stimulator and the Sofa Pillow are two of many effective adult stonefly imitations.

Midge

As the name suggests, midges are tiny insects. They’re most prevalent in lakes and slow-moving streams. Midges metamorphose as follows:

• egg
• larva
• pupa
• adult

When fishing midge patterns below the surface, fly fishers generally concentrate on the pupal stage, because this is the stage that’s most important to trout. Once the larva has matured, it pupates, at which time the pupa begins its slow ascent to the surface in hopes of hatching into an adult. But on the way up, emerging pupae are often ambushed by hungry trout. Popular pupae patterns include the Midge Pupa in various colors, as well as the Brassie and Chironomid Pupa.

If the pupa does make it to the surface, it hatches into an adult midge. Adult midges have 2 wings and no tails. At rest, their wings are swept back at a 45-degree angle like a housefly. The Adams and the Mosquito are two of the most successful adult midge patterns.

Other Important Insects

In ponds and lakes, trout love to feast on the nymphs of dragonflies and damselflies. Both dragonfly and damselfly nymphs have 6 legs and large, wide-set eyes. Dragonfly nymphs – the larger of the two – can take up to 4 years to mature and reach lengths of up 2″. To imitate the dragonfly nymph, tie on a Whit’s Dragon, Carey Special, Doc Spratley or Woolly Bugger. The Hare’s Ear, Zug Bug and Woolly Worm can all be used to imitate the damselfly nymph.

At times, terrestrials such as grasshoppers, ants, beetles and crickets find themselves in the water, being gulped up by ravenous trout. This is especially true on lakes and rivers that are lined with overhanging brush, and on windy days when these insects are blown into the water. To be prepared for these situations, always carry a few terrestrial patterns. Popular ones include the Fur Ant, Dave’s Cricket and Joe’s Hopper, just to name a few.

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