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.

Reference · Hatches

Hatch Calendar

What to expect on UK, Irish, and European waters, month by month — timing shifts with altitude, latitude, and water temperature.

5 min readUpd 26 Apr 2026Reference← Learn

Seasonal rhythm

Spring

Olives & grannom

LDO, March brown, iron blue — midday

Summer

Sedges & terrestrials

BWO, the evening rise

Autumn

Daddy & fry

Trout fatten before winter

Winter

Midges & grayling

Deep nymphs through the cold

Orders:MayflyCaddisStoneflyMidgeTerrestrial

Evening comes alive. BWO spinner falls at dusk, the first sedges fluttering at last light, and the tail end of Mayfly on loughs. The long evenings are magic — arrive at 5pm and fish until dark.

Related Guides

Mayflies

Lifecycle, identification, fly matching

→

Caddis

Sedge ecology and tactics

→

Diptera

Midges, crane flies, hawthorn

→

Dragonflies & Damsels

Stillwater predators

→

Reservoir Entomology

Buzzer-dominated stillwaters

→

The Fishing Year

Month-by-month strategy

→

Fly Box

Search patterns by name

→

Euro Nymphing

Modern subsurface methods

→

Irish Loughs

Lough traditions and hatches

→

Grayling

Winter fishing and nymphing

→

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

January–February

March

April

May

June

July

August

September

October

November–December

Related Guides

Temperature matters