Upwinged flies — olives, mayfly & caenis

What it is

Upwinged flies (Ephemeroptera) — olives, the mayfly or green drake, and caenis — are the classic four-stage insect: egg, nymph, dun and spinner. Trout key onto whichever stage is available at the moment: the nymph underwater, the emerging dun in the film, or the spent spinner lying on the surface. A fly angler doesn't need to be an entomologist, but knowing which stage is happening is the difference between a generic nymph and a genuine tactical decision on size, depth and presentation.

Life cycle

In Ireland

The mayfly (Ephemera danica) hatch is the single biggest seasonal event on the Irish limestone loughs — Corrib, Mask, Sheelin, Conn and Lene all carry strong hatches concentrated from mid-May to early June, and it drives more dedicated fly patterns in the catalogue than any other natural.

Olives (mainly Baetis species — small dark olive, pale watery, and the larger lake olives) hatch through spring and again into early autumn, often best on dull, overcast days. Caenis ("the angler's curse") bring dense hatches on calm summer mornings and dusks, with a life cycle from dun to spinner to spent in under an hour and hook sizes down to 20–24, needing fine tippet.

Flies that imitate this

Illustration

Dry

Olive Dun

#12–14

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Nymph

Olive Nymph

#12–14

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Dry

Adams

#12–16

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Dry

Grey Duster

#12–16

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Wet fly

Greenwell's Glory (wet)

#12–14

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Nymph

Gold-Ribbed Hare's Ear

#12–14

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Dry

Dry Mayfly

#8–12

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Nymph

Mayfly Nymph

#10–12

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Emerger

Mayfly Emerger

#10–12

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Dry

Green Wulff

#10–12

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Dry

Grey Wulff

#10–12

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Wet fly

Gosling

#8–12

Dry

Spent Gnat (Mayfly Spinner)

#10–12

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Dry

Caenis Spent Spinner

#16–18

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Wet fly

Golden Olive Gosling

#10

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Wet fly

Gorgeous George

#8–12

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Wet fly

French Partridge Mayfly

#10

Where it matters