When does the Grannom hatch?

April–May, typically 11:00–14:00. It starts from about 8°C, peaks around 12°C and tails off by 18°C.

What flies imitate the Grannom?

Grannom, Elk Hair Caddis, Apple Caddis, typically on a #16–14 hook.

How big is the Grannom?

Adult stage: 7–10mm. That matches a #16–14 hook.

Caddis · Aquatic insect

Grannom

Brachycentrus subnubilis

Size

7–10mm

Hook size

#16–14

Hatch window

Season April–MayPeak time 11:00–14:00

Water temperature

12° peak

8°18°

How fish feed on it

Unusual among our caddis: it doesn't trickle off over weeks, it goes at once. A April morning can be nothing until suddenly the air over the river is full of them, dense enough to walk into. The green egg sac on the returning females is the detail that matters — it's why a green-butted pattern outfishes a plain one, and why the Spanish Salmón works so well.

Flies that imitate this

Grannom

Elk Hair Caddis

Apple Caddis

Ecology

Rivers & stillwaterSpate riversAlpine riversFreestone rivers

Where you'll find this

British IslesCommon
Atlantic fringeCommon
Continental EuropeOccasional
The AlpsOccasional
ScandinaviaScarce

Common Occasional

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