Midges are the bug that keeps you fishing 365 days a year. They are tiny, they are unglamorous, and on most tailwaters they are the single most important food source a trout has. When the river is locked in January and nothing else is moving, the fish are still eating midges — which means you can still catch them.
Why Midges Rule the Tailwater
Midges (the family Chironomidae, order Diptera — true two-winged flies) hatch every month of the year and breed in phenomenal numbers, especially in the cold, stable, nutrient-rich water below dams. On a classic tailwater — the San Juan, the South Platte, the Bighorn — midges can make up the majority of a trout's annual diet. Fish that see midges constantly get very good at eating them and very picky about imitations, which is exactly why midge fishing is both essential and humbling.
The Life Cycle — Three Stages, All Tiny
1. Larva
Worm-like, in the silt and gravel
The midge larva is a thin, segmented, worm-like creature — often bright red (a "bloodworm"), olive, or cream. It lives in the bottom and is constantly available. A Zebra Midge (a bare hook, a thread body, fine wire rib, and a bead) in size 18–22 is the definitive larva/pupa imitation and one of the most effective trout flies on earth.
2. Pupa
Rising and hanging in the film — the key stage
The pupa ascends slowly and then hangs suspended just under the surface film, struggling to break through. This is where fish do most of their midge feeding, and it's why a midge pattern fished just below the surface — a Mercury Midge, a RS2, a sparkle pupa — outproduces a dry most of the time. The Mercury series uses a tiny silver-lined glass bead to imitate the gas bubble of the emerging pupa.
3. Adult
Tiny, two-winged, clustered on top
The adult looks like a miniature mosquito (it doesn't bite). Individually they are nearly impossible to imitate and barely worth a trout's effort — so the fish wait for them to clump. See the cluster section below.
The Workhorse Patterns
- Zebra Midge (18–22) — black or red body, silver or copper wire, small bead. The default larva/pupa. Carry a pile of them.
- Mercury Midge (20–24) — the silver-bead emerger; deadly hung in the film on pressured tailwaters.
- RS2 (20–24) — a gray or olive emerger that doubles for midges and small mayflies.
- Griffith's Gnat (18–22) — the dry that imitates a cluster of adults, not a single midge.
The Two-Fly Midge Rig
Because the takes are subtle and the flies are nearly weightless, the standard approach is a two-fly nymph rig under a small indicator or below a dry.
The classic stack: A slightly heavier Zebra Midge as the point (lower) fly to get down, and a lighter emerger — a Mercury Midge or RS2 — as the dropper 12–18" above it, riding higher in the column. You cover the larva on the bottom and the pupa in the film in one drift. Go small, go light on tippet (6X or 7X fluorocarbon), and watch the indicator like a hawk — midge eats are featherlight.
Fishing the Cluster
On cold, still mornings, midge adults raft together into mating clusters — little balls of insects drifting on the surface. A single size-24 adult isn't worth a big trout's time, but a cluster is a real mouthful, and fish will rise steadily to them with quiet, deliberate sips. This is when a Griffith's Gnat — which looks like a clump of midges rather than one — shines. Look for slow, glassy water, pods of rhythmically sipping fish, and tiny black specks on the surface. Match the cluster, not the individual.
Can't see your size-24 dry? Fish it 12" behind a more visible fly, or grease a slightly larger Griffith's Gnat and watch the general area — set on any rise near your fly. With midges, an educated guess on a quiet sip beats straining to track an invisible hook.
The hatch calendar flags midges as a year-round staple — they are the answer on the winter and early-spring days when the calendar looks otherwise empty.
Fish year-round.