What do stream trout eat during the winter? With the expanded catch-and -release season now underway on southeastern Minnesota streams, winter anglers can expect to find insect hatches they might not have encountered before. Several members of the midge family are only present as adults in the winter, and they produce special antifreeze molecules within their bodies to tolerate frigid temperatures once they emerge from the stream. The most abundant of these midge species in southeastern Minnesota is Diamesa mendotae, which resembles a mosquito in both size and body shape. It is common to see swarms of them crawling on streamside snow banks, and a single trout may consume several hundered midges on a cold winter day.
Brachycentrus caddisflies also make up a significant portion of winter trout diets. Caddisfly larvae, often green or brown in color, detach from rocks and are picked off by trout as they drift through the water column. Aqatic amphipods, commonly known as scuds or freshwater shrimp, are another important winter food source for trout, especially in streams with abundant aquatic vegetation.
Interestingly, trout have been known to eat frogs that hibernate in many Minnesota streams. Larger trout also eat plenty of fish such as minnow, sculpin and even other trout. Mice and shrews are on the menu as well, so anglers would be wise to experiment with different size offerings. Vaughn Snook, Lanesboro assistant area fisheries supervisor, and Will French, DNR fisheries specialist.