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Grannom (Brachycentrus spp.)
Caddis, hatching April–May, active in water between 48 and 58°F, and imitated at #14–16. Recorded from every region this map covers, across Michigan, Wisconsin, Virginia, North Carolina and Minnesota.
The first big caddis of spring, and often the first time all year that fish look up in numbers. It is a dark insect — black-brown body, mottled tent-shaped wings, and on the female a bright green egg sac at the tip of the abdomen — coming off in dense, blanket swarms in late April, with April and May the peak and afternoon the time of day. The band is 48 to 58 degrees, cold and cold-transitional water, and imitations run size 14 to 16. The larva builds a square-sided case of plant material and lives in it, so a cased-caddis imitation is a legitimate year-round fly. The pupa cuts free and rises fast, which is why a swung soft-hackle takes fish during the hatch when a dead-drifted dry does not. Adults skitter, and egg-laying females dive through the film — a sunk adult is often what the fish are actually eating.
- #14–16Hook size
- 48–58°FWater, active
- Apr–MayPeak months
- 3Life stages fished
What it is
Caddis · Brachycentrus spp. · larva → pupa → adult
A dark caddis with a black-brown body, mottled tent-shaped wings, and — on the female — a bright green egg sac at the tip of the abdomen. It comes off in dense, blanket swarms in late April.
The first big caddis of spring, and often the first time all year fish look up in numbers. Afternoon.
When it hatches
The months below are this site's shared calendar, which covers 8 regions at once. In southeast Minnesota the state's own source says May–June, and the Minnesota page is built on that instead.
Peak is April–May. 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 48°F to 58°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 |
|---|---|
| larva | Builds a square-sided case of plant material and lives in it. A cased-caddis imitation is a legitimate year-round fly on grannom water. |
| pupa | The pupa cuts free and rises fast, which is why a swung soft-hackle takes fish during the hatch when a dead-drifted dry does not. |
| adult | Tent-winged, dark, and skittering. Egg-laying females dive through the film, and a sunk adult is often the fly the fish are actually eating. |
Matching flies
6 patterns in this book imitate the Grannom, 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.
- CDC Caddis dry fly · #14–20 — Lower in the film than an Elk Hair. For flat water and educated fish.
- Little Black Caddis Pupa emerger · #16–20 — Dark body, sparse soft hackle. Swung through the tail of a run in April, which is where the naturals are going.
- Elk Hair Caddis dry fly · #12–20 — Floats forever, skates on command, works when nothing is hatching.
- Green Caddis Larva nymph · #12–16 — Bright green free-living larva. In the drift twelve months a year.
- Hare's Ear Nymph nymph · #10–18 — Looks like everything and nothing. The other half of a two-nymph rig.
- LaFontaine Sparkle Pupa emerger · #12–18 — The gas-bubble pupa. Fished rising through the swing, which is how caddis actually emerge.
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.
- Smith River the Virginia mountains · July mean 51.9°F
- Camp Branch the Virginia mountains · July mean 56.0°F
- Ararat River the North Carolina mountains · July mean 49.9°F
- Back Creek the Virginia mountains · July mean 49.9°F
- Big Cherry Creek the Virginia mountains · July mean 49.9°F
- Big Ivy Creek the Virginia mountains · July mean 49.9°F
- Boothe Creek the Virginia mountains · July mean 49.9°F
- Brogan Branch the Virginia mountains · July mean 49.9°F
- Browns Dan River the Virginia mountains · July mean 49.9°F
- Brushy Fork the Virginia mountains · July mean 49.9°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 Upper Peninsula 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
- Au Sable River
- Catawba River
- Jackson River
- Muskegon River
- Escanaba River
- Saint Croix River
- Smith River
- Tygart Valley River
- Kalamazoo River
- Aaron Creek
- Aaron Run
- Aarons Run
- Abb Run
- Abes Run
- Abitosse Creek
- Abram Creek
- Acme Creek
- Acorn Branch
- Adamcamp Branch
- Adams Creek
- Adams Creek
- Adamson Run
- Addis Creek
- Adkins Rockhouse Branch
- and 6470 more
Related hatches
Same family, or overlapping this one's calendar on the same water.
- Little Black Caddis Chimarra atterima · Caddis · April–May
- Green Rock Worm / Green Weenie Rhyacophila spp. · Caddis · April–June and September–October
- Spotted / Tan Caddis Hydropsyche spp. · Caddis · May–August
- Green Sedge Rhyacophila spp. · Caddis · May–August
- Little Sister Caddis Cheumatopsyche spp. · Caddis · June–August