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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 6 of the 8 regions this map covers, across Michigan, Wisconsin, Virginia, North Carolina and Minnesota.
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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
The months below are this site's shared calendar, which covers 6 regions at once. In southeast Minnesota the state's own source says June, and the Minnesota page is built on that instead.
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.
- Camp Branch the Virginia mountains · July mean 56.0°F
- Abram Creek the Virginia mountains · July mean 57.7°F
- Cranberry Run the Virginia mountains · July mean 57.7°F
- Deep Run the Virginia mountains · July mean 57.7°F
- Emory Creek the Virginia mountains · July mean 57.7°F
- Howell Run the Virginia mountains · July mean 57.7°F
- Johnnycake Run the Virginia mountains · July mean 57.7°F
- Linton Creek the Virginia mountains · July mean 57.7°F
- Mikes Run the Virginia mountains · July mean 57.7°F
- Mill Creek the Virginia mountains · July mean 57.7°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
- Au Sable River
- Catawba River
- Jackson River
- Muskegon River
- Smith River
- Tygart Valley River
- Kalamazoo River
- Aaron Creek
- Aaron Run
- Aarons Run
- Abb Run
- Abes Run
- Abram Creek
- Acme Creek
- Acorn Branch
- Adamcamp Branch
- Adams Creek
- Adamson Run
- Addis Creek
- Adkins Rockhouse Branch
- Aiken Mill Creek
- Alabaster Whitney Drain
- Alarka Creek
- Aldrich Branch
- and 4420 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