Trout are opportunistic freshwater feeders, with insects forming a significant portion of their diverse diet. Their feeding habits are largely influenced by prey availability, allowing them to thrive in various aquatic ecosystems.
Primary Aquatic Insect Prey
Mayflies (Ephemeroptera) are a fundamental food source for trout, particularly during their nymph, dun (emerging adult), and spinner (adult) stages. Mayfly nymphs reside underwater, making them available to trout feeding below the surface. When nymphs ascend to the surface to transform into duns, they become especially vulnerable, often triggering feeding frenzies. Adult spinners, after mating, fall onto the water’s surface, providing another easy meal.
Caddisflies (Trichoptera) are a key part of a trout’s diet, especially in spring. Trout consume their larvae, which often build protective cases, as well as the pupae. As pupae rise to the surface to hatch, and adults skitter across the water during egg-laying, they become highly attractive to feeding trout.
Stoneflies (Plecoptera) offer a substantial meal due to their larger size. Their nymphal stage, which can last for years underwater, provides a consistent food source for trout year-round, even in colder months. Unlike mayflies and caddisflies, stonefly nymphs typically crawl to the shore to emerge as adults, but adults can fall back into the water, becoming available prey.
Midges (Chironomidae) are small but important in trout diets, particularly in cold waters and in winter. Trout feed on their larval and pupal forms, which are abundant in various water types. Midge pupae often rise through the water column, and adults can form dense swarms on the surface, making them accessible.
Dragonflies and Damselflies (Odonata) contribute to the trout’s diet primarily in their nymph stages. These larger nymphs reside among vegetation and silt on the bottom of lakes and slower river sections. Trout prey on them as they forage or move through their aquatic habitat.
Key Terrestrial Insect Prey
Ants (Formicidae) are an important food source for trout, especially during warmer months. These land-based insects often fall or are blown into the water from overhanging vegetation, becoming easy targets. Trout consume both winged and wingless ants, with some studies suggesting ants can make up a significant percentage of a trout’s diet.
Beetles (Coleoptera) are another common terrestrial insect that ends up in trout streams. Various types of beetles, including those that fall from trees and shrubs, provide a consistent food source. Trout readily consume beetles, which are available from early spring through late fall.
Grasshoppers and crickets (Orthoptera) are significant prey in late summer and early fall, especially near grassy banks. These larger insects, known for their clumsy landings, create a noticeable “plop” when they fall into the water, attracting trout. When abundant, grasshoppers can trigger aggressive feeding behavior.
Caterpillars and other larvae from streamside vegetation also provide occasional meals for trout. When these larvae drop, they become available to fish.
Environmental Influences on Feeding
Seasonal changes influence the types and abundance of insects available to trout. In spring, aquatic insect hatches, such as mayflies and caddisflies, prompt increased feeding activity. As summer progresses, aquatic insect activity may wane, and trout shift focus to terrestrial insects. Cooler autumn temperatures can increase trout activity, with some aquatic hatches reoccurring alongside continued terrestrial availability.
Insect “hatches” are periods when aquatic insects emerge in large numbers from the water to transform into adults. During a strong hatch, trout often become highly focused on these emerging insects, losing some caution. Recognizing these concentrated emergence events helps identify when trout will feed heavily on a particular insect type.
Water conditions, including temperature and flow, directly affect insect activity and trout feeding behavior. Trout are cold-blooded, so their metabolism and activity levels are tied to water temperature. Ideal water temperatures for active feeding typically range from 55 to 58 degrees Fahrenheit, though trout will feed in colder water as well. High flows can dislodge aquatic nymphs, making them more available, while extreme temperatures can stress fish and reduce feeding.
The surrounding habitat also dictates the availability of terrestrial insects. Overhanging trees and grassy banks provide a source of ants, beetles, and grasshoppers that can fall or be blown into the water. Abundant streamside vegetation increases the likelihood of terrestrial insects contributing to a trout’s diet. These environmental factors create a dynamic menu for trout.