Trico
Tricorythodes spp.
- Hook size
- #20-24
- On the water
- Jul 10 – Sep 30
- Peak
- Jul 25 – Sep 10
- Time of day
- Morning
No hatch punishes a sloppy presentation like this one. The Trico comes off in clouds so dense they can look like smoke over the water, but each insect is barely the size of a grain of rice. Trout settle into a rhythm, counting calories one at a time, and refuse anything that drags even slightly.
Telling it apart
- Tiny: size 20–24, a body barely 3–4 mm long.
- Near-black thorax on the male; pale cream-to-olive abdomen on the female — from a distance, the swarm just looks black.
- Only two tails, not three — unusual for a mayfly built like this.
- Only one functional pair of wings; the hindwings are reduced or missing.
- A flattened, clinging nymph found on rock and submerged vegetation in slower, slightly silty stretches.
Easily confused with
Caenis, just as tiny and just as reduced in the hindwing, but it emerges toward evening and its fall is thin and scattered — never the dense morning cloud a Trico produces. A very small Baetis can also fool you at a glance, but it keeps three tails and two clearly visible pairs of wings.
A lightning-fast turnaround
Most of our mayflies take a full day, sometimes more, between the dun stage and the final molt to the spinner. A Trico does it in about an hour, sometimes less. The nymph climbs to the surface before dawn or early in the morning, molts almost immediately, and is already a spinner before most anglers have finished their coffee.
The practical result: you almost never see the dun. What you actually see on the water, in the vast majority of cases, is already the spinner fall — the real emergence happened while nobody was watching.
Why mornings
The spinner fall follows temperature, not the clock. It starts once the air has warmed enough for males to form their mating swarms over the water — typically between 7 and 10 a.m., once the dew has burned off. Later in summer, when mornings are already warm at sunrise, the whole show can happen an hour earlier.
Trico runs several generations between July and the end of September, which is why the active window lasts three full months rather than the one or two weeks typical of most of our larger mayflies.
A tippet question, not a fly-pattern one
With an insect this uniform and this abundant, trout build a very precise search image, and any deviation in your fly's silhouette stands out. In the vast majority of refusals, it is not the pattern — it is 5X leaving a visible wake at this size.
Drop to 6X, sometimes 7X, and watch for quiet dorsal-and-tail rises — a very restrained sipping motion from a fish that never moves off its lie. That is the best sign it is genuinely keyed on the spinners rather than gulping at random.
Fishing it, stage by stage
Nymph
Before dawn and early morning, on the bottom.A small dark nymph dead-drifted near bottom in moderate current. Mostly useful as a searching pattern outside the fall — the real action happens on top.
Spinner (the fall)
Roughly 7 to 10 a.m., once the dew has burned off.A spent-wing spinner lying flat in the film, drifted drag-free on 6X or 7X. A Griffith's Gnat also works well as a cluster of several stuck-together spinners rather than a single insect.
Every other insect worth knowing, month by month: See the full hatch chart