Trout are opportunistic predators with a broad diet, constantly seeking meals in both aquatic and terrestrial environments. Insects, in particular, form a significant part of their sustenance, providing crucial energy throughout the year.
Key Aquatic Insect Prey
Aquatic insects represent a primary food source for trout, with several groups being particularly important throughout their life stages. Key groups include:
- Mayflies (Ephemeroptera): A staple, consumed as nymphs, emergers, and adults. Nymphs are a consistent food source, while adults are eaten during emergence or when laying eggs.
- Caddisflies (Trichoptera): Trout feed on their larval, pupal, and adult forms. The pupal stage is especially vulnerable as they swim towards the surface to emerge.
- Stoneflies (Plecoptera): These larger aquatic insects provide a substantial, year-round meal as nymphs, which can live for up to three years underwater. Adults are eaten when they fall into the water or return to lay eggs.
- Midges (Chironomidae): Though small, midges are consumed in vast numbers year-round, especially in colder months. Trout target larvae, pupae, and adults, often focusing on pupae ascending the water column.
Terrestrial Insects and Opportunistic Feeding
Trout supplement their diet with terrestrial insects, which fall or are blown into the water, particularly during warmer months. This opportunistic feeding allows them to capitalize on readily available food sources, including:
- Grasshoppers (Orthoptera): A favored insect, especially during summer and early fall, due to their size and clumsy flight.
- Ants (Formicidae): Consumed during swarming and migratory phases when large numbers may fall into the water.
- Beetles (Coleoptera) and Crickets (Gryllidae): These also contribute to their diet when they enter the aquatic environment.
Other Aquatic Invertebrates
Beyond insects, trout consume various other aquatic invertebrates, including:
- Freshwater shrimp (Amphipoda): Also known as scuds, these are a year-round food source, abundant in productive waters.
- Sowbugs (Isopoda): Small crustaceans that add to the diversity of their benthic diet.
- Leeches (Hirudinea): A consistent, calorie-rich food item, especially in lakes, available year-round.
- Worms: Earthworms and red worms become available after heavy rains wash them into streams.
- Snails (Gastropoda): Consumed, particularly in lake environments where they can be a significant diet component.
Environmental Influences on Trout Diet
Trout diet is influenced by environmental factors. Seasonality plays a significant role, as different insect species emerge or become abundant at various times of the year, such as stoneflies in spring or grasshoppers in summer. Water temperature affects insect activity and trout metabolism, with warmer temperatures increasing both. Water flow and conditions also impact food availability, as high water events can dislodge insects. The specific habitat type, whether a river, stream, or lake, determines the dominant prey species, and trout are adaptable feeders, consuming what is most readily available.