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March Brown (Maccaffertium vicarium)
Mayfly, hatching May–June, active in water between 50 and 62°F, and imitated at #10–12. Recorded from the Wisconsin driftless, where 364 Wisconsin rivers on this site carry a page.
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A large, heavily mottled mayfly, size 10 to 12, with brown-barred wings and a tan-brown body, peaking in May and June. It emerges sparsely over hours rather than in a burst, which is a different kind of fishing from a blanket hatch: one fly here, another twenty minutes later, spread across the afternoon. The sparseness works in the angler's favour, since individual duns get eaten rather than lost in a crowd. The nymph is a flattened clinger built for fast, shallow riffles, holding to the underside of rocks and available all season. At dusk the Great Red Spinner falls with a rust-brown body. The active water temperature band runs 50 to 62 degrees, covering cold and cold-transitional water. Hare's Ear 10 to 18 and Prince 10 to 18 cover the nymph; a March Brown 10 to 12, Parachute Adams 12 to 20, or Red Quill Spinner 12 to 16 cover the surface.
- #10–12Hook size
- 50–62°FWater, active
- May–JunPeak months
- 4Life stages fished
What it is
Mayfly · Maccaffertium vicarium · nymph → emerger → dun → spinner
A large, heavily mottled mayfly, size 10 to 12, with brown-barred wings and a tan-brown body. It emerges sparsely over hours rather than in a burst, which is a different kind of fishing from a blanket hatch.
Never thick, always spread across the afternoon. A big dun trickling off all day is worth more than a blizzard of small ones.
When it hatches
Peak is May–June. 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.
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.
Active from 50°F to 62°F. On this map that is cold, cold-transitional water — the band crosses 1 of the three break 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 flattened clinger built for fast, shallow riffles. It holds to the underside of rocks and is available all season. |
| emerger | Sporadic, spread across the afternoon. One fly here, one twenty minutes later. |
| dun | Big and mottled, easy to see. The sparseness means individual duns get eaten rather than lost in a crowd. |
| spinner | The Great Red Spinner, falling at dusk with a rust-brown body. |
Matching flies
5 patterns in this book imitate the March Brown, 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.
- Hare's Ear Nymph nymph · #10–18 — Looks like everything and nothing. The other half of a two-nymph rig.
- March Brown dry fly · #10–12 — A large mottled dun for late May afternoons.
- Parachute Adams dry fly · #12–20 — Universal mayfly dun imitation. Every angler carries these.
- Prince Nymph nymph · #10–18 — An attractor nymph with biot wings. Nobody agrees what it imitates and it does not matter.
- Red Quill Spinner dry fly · #12–16 — The Hendrickson male, and the evening fall after the hatch.
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.
- Black Earth Creek the Wisconsin driftless · July mean 61.6°F
- Glenn Creek the Wisconsin driftless
- Pigeon Creek the Wisconsin driftless
- Ranch Creek the Wisconsin driftless
- Robinson Creek the Wisconsin driftless
- Suukjak Sep Creek the Wisconsin driftless
- Wyman Creek the Wisconsin driftless
- Baraboo River the Wisconsin driftless · July mean 62.2°F
- Billings Creek the Wisconsin driftless · July mean 62.2°F
- Brandy Creek the Wisconsin driftless · July mean 62.2°F
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
- the Virginia mountains VA
- the North Carolina mountains NC
- southeast Minnesota MN
Rivers in these regions with a page here
- Allen Creek
- Apple Branch
- Ash Creek
- Badger Mill Creek
- Bailey Creek
- Baker Creek
- Baraboo River
- Basswood Creek
- Bear Creek
- Bear Creek
- Bear Creek
- Beaver Creek
- Beaver Creek
- Beaver Creek
- Big Creek
- Big Creek
- Big Rock Branch
- Big Spring Branch
- Big Spring Creek
- Billings Creek
- Bishop Branch
- Black Earth Creek
- Bohn Creek
- Bostwick Creek
- and 340 more
Related hatches
Same family, or overlapping this one's calendar on the same water.
- Light Cahill Maccaffertium ithaca · Mayfly · May–July
- Little Sulphur Ephemerella dorothea · Mayfly · May–July
- Sulphur Ephemerella invaria · Mayfly · May–July
- Green Drake Ephemera guttulata · Mayfly · May–June
- Large Blue-Winged Olive Drunella cornuta · Mayfly · May–June