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Mayflies (Order: Ephemeroptera)

A photograph of a mayfly resting on bracken.

Mayflies are very shortlived as adults. Most only live between one and four days.

This is a small group of aquatic insects, often referred to as Mayflies. The name comes from a Greek word meaning 'living a day' due to the adults having very short lives, usually between one and four days only. There are a little under 50 British species of Mayfly.

Main characteristics of Mayflies

Transparent wings, of which the forewings are larger than the hindwings.
Occasionally the hindwings are absent
Three long tail filaments, unlike Stoneflies
Very short antennae
Wings held over their backs when at rest, unlike the similar Stoneflies
No food is taken
The males are often seen swarming over the surface of the water
A weak flight

Life-cycle

The eggs are laid in or on fresh water, the female often dipping her abdomen below the surface as she flies
The nymphs live in the water
The nymphs have gills, each generally a single or double plate attached to the side of the abdomen.
They are herbivores feeding on algae and plant detritus
Some are able to produce up to 3 generations a year, whilst others may take up to 3 years to mature
When ready to emerge, they come top the surface of the water and break free of the final nymph skin and fly weakly as a subimago
Unlike any other insect, they still need to moult one more time before they are able to fly properly and reproduce

Swarms of males perform a mating 'dance' over the surface of the water. When a female is found, the male flies beneath her, grasping her with his long forelegs and a pair of claspers.

A stout water net and some jars are all that are normally needed in the field for collecting Mayfly nymphs, whilst the adults can be caught in a net of the type used for Lepidoptera. The nymphs can be obtained by sweeping nets through vegetation, or thrusting 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

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