Fly Fishing Entomology 101: Midges

My non-fly fishing friends marvel that fly fishers catch large trout on flies the size of a Tic Tac mint. Catching a 20-inch trout on a size #20 fly (or smaller!) is possible, in part, because of Midges.

Here is a brief profile of these tiny insects that are an important part of a trout’s diet:


    • Midges belong to the insect order “Diptera”—a Greek term meaning “two wings”; and

    • Fly fishers sometimes refer to Midges as “Chironomids” because they belong to the family of insects known by its scientific name, Chironomidae (Latin).

The Basics

    • Midges live in all kinds of water. Midges in rivers are a lot smaller (the average is size 20, though they can range from size 16 to size 24) than those living in ponds are lakes;

    • Midges, like all Diptera, go through complete metamorphosis—larva, pupa, and adult stages; and

    • Midges can have up to five generations a year, so trout feed on them constantly in moving water. This means fly fishers can fish them year round. However, the winter is the best time—especially for dry fly patterns—since they are about the only thing hatching.

The Stages of Midges

    • In their larval stage, Midges live in the bottom of streams and rivers, feeding on algae or on decaying plant or animal matter. Dave Hughes, an Oregon fly fisher and entomologist, does not think fly fishers should spend much time trying to imitate them since they are challenging to imitate and since trout do not seem to feed on them exclusively (like they do at times for the next two stages);

    • The pupal stage may be the most important one for fly fishers. When the larvae reach maturity, they begin pupation and are ready to float to the surface. They do this more by floating than swimming, though they wiggle their abdomens a bit to get started. Once they reach the surface, they are trapped until they break the surface tension. This is a time when trout can go into a feeding frenzy. It may look like they are feeding on Midges on the surface. But the trout are actually feeding on Midges in the surface film or just beneath it. Although pupae emerge throughout the day, they show up in larger numbers in the afternoon—and sometimes into early evening; and

    • Midges enter their adult stage once they push through the surface film. In colder months, they float longer, waiting for their wings to harden before they fly away. Mating occurs either on land, in the air, or even in the water. Since they come off the water in great numbers, Midges often form clusters. At times, trout may focus more on these clumps of Midges — a larger meal!—than singles.

Effective Patterns

    • A Zebra Midge, a Brassie or a Krystal Flash Midge can imitate Midges in their larval stage;

    • Midge pupa patterns are legion, so you might need to visit a fly shop and ask for help. Some of the more effective patterns, though, for Midge pupae include the Biot Midge Pupa or the Traditional Midge Pupa. The CDC Transitional Midge or CDC Stillborn Midge are great choices, too, since they imitate the Midge in its transition—or failure to transition—between the pupa and adult stage;

    • For the Adult stage, my favorite patterns – that work well especially for a cluster of Midges – include the Griffith’s Gnat, the Renegade, and the Parachute Adams. Keep in mind that you may have to go to sizes 22 to 26 if you are trying to imitate a single Midge! That’s why I prefer to imitate the clusters.

Other Entomology 101 Articles & Sources

    Fly Fishing Entomology 101: Midges

    Fly Fishing Entomology 101: Blue-Winged Olives

    Fly Fishing Entomology 101: Caddisflies

    Fly Fishing Entomology 101: Pale Morning Dun

    Sources: Dave Hughes, Jim Schollmeyer, Bob Granger

2 Replies to “Fly Fishing Entomology 101: Midges”

  1. Thank you for this post! Once again, it is very timely in that we are heading out to fish gold medal tailwaters in just a few weeks. Thank you for such great information!

Comments are closed.