Plecoptera - the Stoneflies

On most spate rivers and upland streams stoneflies are a vital source of trout food, particularly in spring and autumn.

Large Stonefly
Orange-striped stonefly, Perlodes mortoni
February Red
February Red, Taeniopteryx nubulosa
Yellow Sally
Yellow Sally, Isoperla grammatica

Flies of this order, which contains around thirty species in the British Isles, are also known as the hard-winged flies.

Life Cycle

The stonefly has a life cycle similar to that of an upwinged fly except that there is only one winged adult stage.

Yellow Sally stonefly larva

Nymphs

Stonefly nymphs have two tails, and so they can be immediately distinguished from the three-tailed nymphs of the upwinged flies.

Yellow Sally adult

Adult stoneflies

Stoneflies generally hatch by crawling out onto stones in shallow water or up emerging vegetation. This method of hatching is not an easy antic to mimic without the artificial fly getting snagged on the bottom. The adult stoneflies are therefore of greatest importance to flyfishers.

Most of the stoneflies of early and late season are dark brown or grey, often with a yellowish tinge to the underside of the body. Apart from the dark stoneflies, there are also two very common summer species with yellow wings and a few others with mottled brown wings.

After mating, the female stonefly lays her eggs, either by dropping them on to the water or by dipping down to the surface. Spent stoneflies often struggle and sink below the surface film; perhaps that is why some of the most effective imitations are tied in a spidery wet fly style.

References

Pryce, D., Macadam, C., & Brooks, S. (2007) Guide to the British Stonefly (Plecoptera) Families: adults and larvae. Taunton: Field Studies Council.

Hynes, H.B.N. (1977) Adults and Nymphs of British Stoneflies (Plecoptera). Ambleside: Freshwater Biological Association.


Pat O'Reilly

If you found this information helpful,we are sure you would also find the new 2017 edition of our bestselling book Matching the Hatch by Pat O'Reilly very useful. Get an author-signed copy here...

Other nature books from First Nature...