Electrogena lateralis - Dusky Yellowstreak

Phylum: Arthropoda - Class: Insecta - Order: Ephemeroptera - Family: Heptagenidae

Electrogena lateralis, Dusky Yellowstreak, male dun
Dusky Yellowstreak dun (male)

The nymph of the Dusky Yellowstreak (also referred to as the Dark Dun) is a stone clinger and is far more common on spate rivers than on chalk streams; it also occurs on some upland lakes that have shallow stony shores exposed to the wind. This fly is fairly common on the River Teifi in West Wales, our home river, and on many other Welsh spate rivers.

Electrogena lateralis, Dusky Yellowstreak, female dun

A female dun of the Dusky Yellowstreak

Dun or subimago

The main hatch of Dusky Yellowstreaks usually begins in late afternoon throughout the summer months. Unusually for a mayfly, the nymphs eclode on the riverbed in riffle sections and the duns surface, generally in sparse numbers, and very soon fly off into surrounding vegetation. The female is similar to the male, but with noticeably smaller eyes.

Electrogena lateralis, Dusky Yellowstreak, female spinner

A male spinner of the Dusky Yellowstreak

Flyfishers do not need a close imitation of the Dusky Yellowstreak dun because they emerge in small numbers at a time when very little surface other surface food.

Electrogena lateralis, Dusky Yellowstreak, female spinner
A female spinner of the Dusky Yellowstreak

Spinner or imago

The female spinner of the Dusky Yellowstreak is less dusky than the dun, and its mirror-like shining wings and longer tails distinguish it from the dun. Its wings are transparent, with dark veining.

The males swarm (something of a misnomer, really) in smallish groups and quite often mating occurs well away from the river; so it is the female spinner that can become a trout's dinner. On warm evenings from sunset until dusk the female spinners return to the water to lay their eggs. A sparse fall of spinners can cause a sporadic rise, but a close imitation of the spent spinner is almost certainly not necessary.

The male spinners are similar to the females, but the bodies are rather darker and they have larger eyes. Because they rarely fall to the surface of the river, male spinners are of little interest to flyfishers.

Matching the Hatch

As the nymphs of the Yellow May live under stones during daylight hours, it is only during a hatch that trout have much of a chance to feed on them. A size 14 Gold-ribbed Hare's Ear works fine for imitating the emerging duns, while any size 14 spent spinner will do fine in the dim light of late evening.

If you don't have a copy of Pat O'Reilly's Matching the Hatch, the pictures above gives you something to aim for when devising your own artificial pattern. The main point is not to copy someone else's artificial fly but to try to achieve something which, seen from under the water (the trout's point of view) looks sufficiently like the real thing not to raise suspicion. The final part of the deception, and it can be the most challenging, is to control your fly in or on the water so that it behaves similarly to the natural insect that it is meant to mimic.

Similar Species

Electrogena affinis is a rare (in Britain) close relative of the Dusky Yellowstreak. Sometimes this fly, known only from the River Derwent and tributaries in Yorkshire, is sometimes referred to as the Scarce Dusky Yellowstreak. It favours deeper, slower-flowing stretches with plenty of emergent vegetation.

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