What is a hatch in fly fishing?

A hatch is the emergence of aquatic insects from the water surface. Nymphs living on the riverbed swim or crawl to the surface, shed their exoskeleton, and become winged adults. This transition creates a concentrated food source that trout feed on actively, making it the prime opportunity for fly fishing with imitative patterns.

What insects hatch first in spring?

The Large Dark Olive (Baetis rhodani) is typically the first reliable river hatch, appearing from February onwards when water reaches 5-6°C. Chironomid midges hatch year-round, including through winter. March Brown appears on fast rocky rivers from March when water hits 8°C.

When is the best time to fly fish during a hatch?

It depends on the season. Spring hatches are typically midday (11am-2pm) when water warms. Summer hatches shift to evening (5-9pm) as BWO, sedges, and spinners emerge at dusk. Autumn returns to midday. The key is matching the insect's emergence window, which is driven by water temperature and light levels.

What is the difference between a dun and a spinner?

A dun (subimago) is the freshly hatched mayfly sitting on the water drying its wings — it has opaque, dull-coloured wings. A spinner (imago) is the sexually mature adult that returns to lay eggs — it has clear, glassy wings and falls spent on the surface after mating. Both are important food stages but require different fly patterns.

What flies should I use to match a hatch?

Match the lifecycle stage first, then the species. If trout are taking emergers in the film, use an emerger pattern (Klinkhamer, CDC emerger). If they are taking duns off the top, use a dry fly. If taking spinners, use a spent pattern fished flat. Size matters more than exact imitation — get the hook size right before worrying about colour.

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Hatch Calendar

What to expect on UK, Irish, and European waters, month by month. Timing shifts with altitude, latitude, and water temperature — the insects keep their own calendar. Tap any insect for descriptions, lifecycle tips, and suggested fly patterns.

Seasonal rhythm

🌱 Spring: LDO, March Brown, Grannom, Iron Blue — midday hatches on warming water

☀️ Summer: BWO, sedges, terrestrials, Green Peter — the evening rise

🍂 Autumn: Daddy, autumn olive, fry feeders — trout fatten before winter

❄️ Winter: Midges and deep nymphs — grayling through the cold months

Orders:MayflyCaddisStoneflyMidgeTerrestrial

The pinnacle. Water temperature reaches 12–15°C and the full cast of characters arrives. Mayfly on limestone loughs and chalk streams, Yellow May Dun on fast rivers, the first Blue-Winged Olives, and Yellow Sally stoneflies on mountain water.

Related Guides

Mayflies

Lifecycle, identification, fly matching

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Caddis

Sedge ecology and tactics

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Diptera

Midges, crane flies, hawthorn

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Dragonflies & Damsels

Stillwater predators

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Reservoir Entomology

Buzzer-dominated stillwaters

→

The Fishing Year

Month-by-month strategy

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Fly Box

Search patterns by name

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Euro Nymphing

Modern subsurface methods

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Irish Loughs

Lough traditions and hatches

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Grayling

Winter fishing and nymphing

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Temperature matters

Water temperature is the master variable for hatch timing. Calendar dates are rough guides — what really triggers emergence is accumulated warmth (degree-days) and instantaneous water temperature. A warm March can bring April hatches; a cold May can delay them by weeks. Rise Daisy uses live water temperature data to predict what is likely hatching on your river right now.

Hatch Calendar

Seasonal rhythm

January–February

March

April

May

June

July

August

September

October

November–December

Related Guides

Temperature matters