Fly Fishing Lessons | What Do Trout Eat?

To fly fish for trout effectively, it’s important to be familiar with the food sources that your flies are designed to imitate. Many of the best trout anglers double as amateur entomologists, studying up on common aquatic and terrestrial insects to better understand where and when trout might be feeding on them.

It may seem overwhelming at first, but developing a basic knowledge of the categories of trout food will make you a much better angler in the long run.

Mayflies

When you think of an insect hatch on a trout stream, you’re likely thinking of a mayfly hatch. Adult mayflies have two upright wings that are often said to look like sails on a sailboat, and they’re an important food source on all trout waters.

Before mayflies hatch, they spend most of their life cycle underwater in the nymph stage. Some mayfly nymphs cling to underwater rocks, and some burrow into the streambed, but they become meals for trout when they’re dislodged by current and float downstream.

Caddisflies

Though mayflies are likely the most well-known insect on the trout menu, caddisflies are equally common on most rivers and streams. Adults have tent-shaped wings that fold over the body, and, unlike mayflies that sit still on top of the water, they skitter on the water’s surface.

Like mayflies, caddisflies spend the majority of their life cycle in the nymph stage. Many types of caddis nymphs build protective cases from sticks, sand, and pebbles, giving them a chunkier appearance than slender mayfly nymphs.

Stoneflies

Stoneflies are large, slow-flying aquatic insects that have wings that fold flat against the body. Stoneflies move to dry land immediately after emergence and rest on streamside rocks and vegetation to dry their wings.

Because they don’t spend much time on the water’s surface, fly anglers are primarily concerned with stoneflies in the nymph stage. They use their flat bodies and strong legs to cling to the underside of rocks, and trout eat them when they become dislodged.

Midges

Midges are the smallest of the aquatic insects that comprise the trout diet. They’re a year-round food source, and they’re particularly important for trout in the winter months, when larger insects are less prevalent.

You’ll find flies that imitate midges in the nymph, emerger, and adult stages – mostly tied in size 18 or smaller. Their tiny size makes them difficult to fish, but a well-presented midge can often be a saving grace on an otherwise unproductive cold winter day.

Terrestrials

Similar to the dead of winter, aquatic insect hatches slow down in the hottest months of the year. Thankfully, the summer months feature terrestrial insects that are blown into or fall into the water. When this happens, trout feast on them.

Grasshoppers, beetles, and ants are the most common terrestrial fly patterns, and they provoke some of the best dry fly eats that you’ll see. They’re big, high-protein meals that trout don’t have access to for most of the year, so they get hit hard when they’re around.

Crustaceans, Leeches & Other Fish

While insects make up the majority of a trout’s diet, many trout supplement with other food sources. Because the trout diet is so insect-heavy, many anglers overlook these larger, high-protein meals that play a crucial role in certain trout waters.

Crustaceans, leeches, and smaller fish are important for large trout that live in environments where insect hatches are less common. If you fish for trout in lakes, this food source should make up a large part of your fly box.