Michigan Trout Unlimited
MICHIGAN Trout
Terrestrial Time
20
by Ann R. Miller
Summer 2022
As June begins to wane and mid-summer is imminent, aquatic hatches of mayflies, caddisflies, and stoneflies diminish. Dry fly and nymph fishing for these insects wraps up for another year for anglers. Fish rely heavily on aquatic macroinvertebrates for food for the first half of the year, but once they have hatched, the immature stages are generally slow-growing and not as available as fish food. Some smaller insects such as Tricos, Baetid mayflies, and Dipterans (true flies) have multiple broods during the year (multivoltine) and provide a steady supply of tiny nymphs and larvae. Warmer waters during the summer mean that trout will be active and growing, and additional food is necessary, especially for larger fish. Supplemental food in the form of terrestrial insects suddenly becomes essential in the trout’s diet. While aquatic insects spend at least a portion of their life cycle under water, terrestrial insects are completely land borne and only accidentally end up in the water. Terrestrial insects tend to mature later in the summer, and as they fly or crawl near creeks or rivers, hungry trout can eat them if they errantly land in the water. Studies have documented that in some rivers, terrestrial insects can account for more than 50% of the trout’s diet from late summer to early fall.
intercept one dangling from its tether. Caterpillars that end up in the water will float for some distance but eventually will sink and drown, so patterns that imitate them can be fished both wet and dry. Ballooning is a behavior common with other types of caterpillars as well. Terrestrial insects have a seasonality, and while they aren’t called hatches, activity varies throughout summer and early fall. Beetles are so bountiful that they are common throughout the summer and early fall. Ants actively foraging along tree branches or brush fall into the water daily. However, at certain times of the year, the nests produce alates or winged adults that will go forth and propagate new colonies. Males and females will fly away from the nest and mate; the males will die soon after, while the females will either begin a new colony or become part of an established colony. Termites have similar flights, and rivers that run through forested areas can have both insects. Typically, these flights are in July and August, but I have witnessed a flight in late March. Always stash a few ants and beetles in your fly boxes from the spring onward.
Many terrestrial insects are capable flyers, but some prefer crawling or jumping, while others are incapable of flying. Weather can play a role in knocking insects into the water: hot summers are often accompanied by windy afternoons or violent thunderstorms, which can contribute to displacing an insect. A keen eye or a handy net seine will help an angler on the water to determine which terrestrial insects may have recently become river victims. Different life cycle stages of a terrestrial insect are sometimes more important than another in a trout’s diet. For example, little green inchworms, sometimes called looper caterpillars, are the immature stage of the Geometridae moths. The caterpillars feed on a cornucopia of greenery, including shrubs, trees, flowers, grasses, and more. The Geometer caterpillars move by stretching their front legs forward and drawing up their rear ends using their anal prolegs, forming a loop (or inching along) in the process. They are known to lower themselves from foliage using a silk tether, ballooning around on windy days. This behavior is especially prevalent just prior to their pupation, which takes place on the ground. Inchworms found on plant life along a river are susceptible to being eaten by trout, and it is Gypsy Moths. not uncommon to see a trout jump out of the water to
