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Stoneflies (Order: Plecoptera)

A photograph of an adult Stonefly.
Photograph by Haplochromis licensed under Creative Commons.

This is a small group of aquatic insects, often referred to as Stoneflies. There are a little under 40 British species. Although as adults they resemble in many ways Lacewings and Alderflies, they are more closely related to Mayflies (Ephemeroptera).

Main characteristics of Stoneflies

Transparent wings, of which the hindwings are broader than the forewings.
Two long tail filaments.
wings held flat when at rest.
a life-span of 2 to 3 weeks.
Those species with herbivorous larvae, do take food as adults, as opposed to those with carnivorous larvae, which appear not to.
Mating takes place on the ground.
Many species are reluctant to fly.

Life-cycle

The eggs are laid in or on fresh water, the female dipping her abdomen below the surface as she flies, or having run on to the surface from the river bank.
The nymphs live in water.
Most are formidable carnivores.
When ready to emerge, they come top the surface of the water and break free of the final nymph skin.
They are univoltine (having one generation a year).

A stout pond net and some jars are all that are normally needed in the field for collecting stonefly nymphs, whilst the adults can be caught in a normal butterfly net. The nymphs can be obtained by sweeping through aquatic vegetation, or thrust under stones as they are lifted from the bottom. Living in running water, they should therefore be taken home in as large a volume of water as possible.

Most larvae can be reared without difficulty, but need cold water and some flow.

If a collection of specimens is required, it is preferable to preserve both adults and nymphs in a suitable liquid. Pinned and dried specimens shrivel badly, making identification difficult.

A good stereoscopic microscope is essential for accurate identification of the different species.

Essential reading from the Amateur Entomologists' Society

The Study of Stoneflies, Mayflies and Caddisflies

A to Z of insects

Back to Insect Orders.