When does the Ephemera japonica hatch?

June–August, typically 17:00–20:00. It starts from about 12°C, peaks around 16°C and tails off by 21°C.

What flies imitate the Ephemera japonica?

Sakasa Kebari, CDC Olive Emerger, Comparadun, typically on a #14–12 hook.

How big is the Ephemera japonica?

Spinner stage: 13–17mm. That matches a #14–12 hook.

Mayfly · Aquatic insect

Ephemera japonica (Upstream Keiryu Mayfly)

Ephemera japonica

Size

13–17mm

Hook size

#14–12

Hatch window

Season June–AugustPeak time 17:00–20:00

Water temperature

16° peak

12°21°

How fish feed on it

By the time the spinners are down the fly has finished its job and is simply lying there, spent, wings flat in the film, going nowhere. Trout know the difference between something alive and something that's stopped trying, and they take spinners with a quiet, unbothered sip that's easy to miss if you're still watching for something splashier. Look for them on the glides and in the slack water, wherever the current gathers what's left.

Flies that imitate this

Sakasa Kebari

CDC Olive Emerger

Comparadun

Ecology

Rivers onlyAcid headwaters

Where you'll find this

East AsiaPresent

Present throughout

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