By Dr. Jennifer Biederman

When it comes to the diets of stream-dwelling trout in Minnesota, aquatic benthic invertebrates take most of the spotlight. Keep in mind that trout are visual and opportunistic feeders – so prey preference and capture probability are likely influenced by the accessibility, size, color, mobility, and degree of exposure of various prey types. In Minnesota streams – especially those in the Driftless – the high availability of aquatic invertebrates (high productivity is thanks to the fertile water of the karst landscape) means that stream trout tend to engage in epibenthic feeding (epibenthic = along the rocky stream bottom).

This isn’t true everywhere. Numerous scientific studies have identified a positive selection by brown trout for terrestrial insects – especially in the western United States where terrestrial insects have been shown to make up over 80% of trout diets in certain regions. Research has shown different eating patterns in Minnesota. A 2005 study in Valley Creek (Washington County) found that trout were neutrally selective for terrestrial prey in the summer, which only comprised 3% of all available drifting invertebrates available and of the overall stomach contents. My own PhD research looked at both seasonal diets and the availability of prey (benthic and drifting) in six streams in southeastern Minnesota across three years. Although on a few notable occasions stomachs contained high proportions of terrestrial prey in response to a temporary spike in availability (e.g. ants and aphids following a significant rainfall event in summer), terrestrial insects were very few and far between in stomachs, and only a small portion of prey available.

So, does that mean you should abandon the terrestrial patterns this summer? Nah. Trout are opportunistic, visual feeders. Especially outside of a hatch, trout will still chase after a terrestrial fly – which are really, really fun to fish.

Here are some recommended patterns to tie:

1. Hopper Patterns:
   • Dave’s Hopper: Mimics grasshoppers that are common in summer. Its realistic profile and buoyant construction make it an excellent choice.
   • Parachute Hopper: Floats well and is easy to see, making it ideal for fishing in faster-moving water.
2. Ant Patterns:
   • Foam Ant: Very buoyant and effective, particularly during hot summer days when ants are active.
   • Cinnamon Ant: A realistic pattern that works well when ants are present near the water.
3. Beetle Patterns:
   • Foam Beetle: Easy to tie and highly effective. Its foam body ensures it floats well, and the shiny back can attract attention.
   • Japanese Beetle: Imitates the iridescent beetles that are common in July.
4. Cricket Patterns:
   • Morrish’s Hopper/Cricket: Effective for imitating both hoppers and crickets. It’s versatile and a good general terrestrial pattern.
   • Letort Cricket – Effective for imitating crickets, as well as black caddis in smaller sizes. It’s versatile and a good general terrestrial pattern.
   • Chernobyl Ant: While often used for hoppers, it can also mimic crickets and other large terrestrials.
5. Spider Patterns:
   • Black Foam Spider: Imitates small black spiders that frequently fall into the water.
   • Parachute Spider: Floats well and is highly visible, making it a good choice for varied water conditions.
6. Miscellaneous Terrestrials:
   • Madam X: An attractor pattern that mimics a variety of terrestrials. Its rubber legs provide additional movement that can entice strikes.
   • Fat Albert: A buoyant, multi-colored fly that can imitate hoppers, beetles, and other large terrestrials.

When tying these flies, consider using durable materials to withstand multiple strikes and maintain their effectiveness in the water. Also, adding a bit of flash or using bright colors can help attract trout in various lighting conditions.

What’s a macro and what’s it have to do with trout angling and conservation? Macros are on the trout menu for pretty much every meal. Macro means big and macroinvertebrates, or “macros,” are animals without a backbone, that are big enough to be seen by the human eye. They can be aquatic or land based, however aquatic insects make up the majority of a trout’s diet. They are also, of course, the inspiration for the flies we tie and use to catch trout. Learn about a new macro each month and how you can create your own to take with you on your next fishing trip!