Trico (Tricorythodes spp.)

Mayfly, hatching July–September, active in water between 58 and 72°F, and imitated at #20–24. Recorded from the Wisconsin driftless and northern Wisconsin, where 1611 Wisconsin rivers on this site carry a page.

A tiny black-and-white mayfly, size 20 to 24, whose spinner falls carpet flat water on late-summer mornings through July, August and September. Males are black, females carry a pale olive-green body, and both are smaller than most anglers want to fish. The nymph is a minute dark crawler in silt and weed, rarely imitated and rarely needed. Duns emerge at first light, females in the early morning and males often the night before. The spinner fall is the event: dense, spent, black and white, between eight and eleven in the morning, on water so flat that a size 22 and 7X is not an affectation. Dun at first light, spinner by mid-morning, done by eleven, and it makes for the most technical dry fishing of the year. The active band is 58 to 72 degrees, covering cold-transitional, cool and warm water. Trico Dun and Trico Spinner 20 to 24, Griffith's Gnat 18 to 24, Zebra Midge 18 to 24.

#20–24Hook size
58–72°FWater, active
Jul–SepPeak months
3Life stages fished

Subbasins with trout water where it is on record: 37 of Wisconsin's 43.

See Wisconsin's trout water on the live map → Every reach coloured by water temperature — the water these hatches come off.

What it is

Mayfly · Tricorythodes spp. · nymph → dun → spinner

A tiny black-and-white mayfly, size 20 to 24, whose spinner falls carpet flat water on late-summer mornings. Males are black, females have a pale olive-green body, and both are smaller than most anglers want to fish.

Dun at first light, spinner fall by mid-morning, done by eleven. Tiny flies and long fine tippet — the most technical dry fishing of the year.

When it hatches

Peak is July–September. The pale months either side are the shoulder — the app widens a peak by one month in each direction and recommends the bug there, and no further: that widening is bounded so that a bug peaking in May is never offered in August.

JFMAMJJASOND

peak shoulder not recommended

Water conditions

The band is a water temperature, not an air temperature, and it is the range in which this insect is worth fishing — for a mayfly that is the emergence window; for a scud or a midge it is simply the range trout will still eat one in.

58°F 72°F

Active from 58°F to 72°F. On this map that is cold-transitional, cool, warm water — the band crosses 2 of the three breaks the river colours use. Breaks at 58, 64 and 70°F.

Stages

What the insect is doing, and what that means for what you tie on.

Stage	What it is
nymph	A minute dark crawler in silt and weed. Rarely imitated and rarely needed.
dun	Emerges at first light — females in the early morning, males often the night before.
spinner	The event. A dense fall of spent black-and-white spinners between eight and eleven in the morning, on water so flat that a size 22 and 7X is not an affectation.

Matching flies

4 patterns in this book imitate the Trico, across its stages. Which one to tie on follows the stage the water temperature says it is in — the app makes that call on a live reading; this page lists the whole set.

Where to find it right now

The rivers with a page here that sit in this insect's regions, with a USGS gauge reporting water temperature. This list is re-ranked against the reading each gauge is sending now and today's date, so it is live — the fallback below it, if the readings do not arrive, is each river's measured July mean.

Regional presence

Regions, not collection records. This insect is recorded from the coarse regions below; nobody has surveyed which named river it has been caught on, and this page will not pretend otherwise.

northern lower Michigan MI
southern lower Michigan MI
the Wisconsin driftless WI
northern Wisconsin WI
the Virginia mountains VA
the North Carolina mountains NC
southeast Minnesota MN

Rivers in these regions with a page here

Related hatches

Same family, or overlapping this one's calendar on the same water.

Open the trout map →Every trout stream near you, coloured by today's water temperature.