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Mayfly (Ephemera vulgata)

Known for its short adult life, the mayfly is here for a good time, not a long time. Emerging between May and August, it dances above freshwater rivers and lakes to find a mate.

Mayflies, including Ephemera vulgata, emerge between May and August.

Credit: Jack Perks / Alamy Stock Photo

Mayfly nymphs live in clean, unpolluted rivers, ponds and lakes.

Credit: ImageBROKER GmbH & Co. KG / Alamy Stock Photo

Quick facts

Common name: mayfly

Scientific name: Ephemera vulgata, though there are many different species

Order: Ephemeroptera

Habitat: rivers, ponds and lakes with areas of silt, sand and fine gravel that are clean, unpolluted and have highly oxygenated water

Diet: nymphs feed on algae and vegetation, adults don’t feed

Predators: adults are predated by trout, salmon, swallows, robins, wagtails and flycatchers. Nymphs are predated by amphibians, as well as the larvae of caddisfly, stonefly and dragonfly

Origin: native

What do mayflies look like?

Larvae: known as nymphs, they have long, slim abdomens, a body divided into a number of segments, and six legs. They also have three slender 'tails'.

Adults: there are two adult stages. The sub-imago, or ‘dun’, is the dull, brown-coloured winged form that first emerges from the water. Then, after a second moult, mayflies become an imago, or ‘spinner’, the full adult form. This has a creamy-yellow abdomen with distinctive dark triangular markings, translucent, dark-veined spotted wings and three long tails.

Females are slightly larger than males, while males have larger eyes and a pair of pincers near their tails.

A note of caution when it comes to identifying mayflies: these descriptions are of one type of UK mayfly. There are many others, including green drake mayfly, large dark olive mayfly and large brook dun mayfly.

Credit: blickwinkel / Alamy Stock Photo

How do mayflies breed?

Between May and August, males gather in large swarms and perform an elegant rising and falling dance in an effort to attract a mate. Females will then fly into the swarm, where they’ll choose their partner and mate on the wing.

After mating, the females dip their abdomens into the water and lay their eggs, which fall to the riverbed. They hatch into nymphs, which spend the best part of two years in their larval form before emerging as adults and restarting the cycle.

 

Did you know?

The British Isles are home to 51 species of mayfly.

What do mayflies eat?

Nymphs feed on algae, vegetation and plant matter in their watery homes, where they live for around two years.

Once they become adults they have no functioning mouth parts, so can’t feed, and channel all their energy into breeding.

Mayflies, such as Ephemera vulgata, rest on vegetation.

Credit: Jussi Murtosaari / naturepl.com

Did you know?

Mayflies are older than the dinosaurs. They were the first winged insects to evolve, and there are fossils dating back more than 300 million years.

Where do mayflies live?

Mayflies can be found across the UK and prefer clean, unpolluted wetlands with highly oxygenated water, such as rivers, ponds and lakes. Ideally, they should also have areas of sand, silt, mud or fine gravel where nymphs can burrow.

Signs and spotting tips

Adult mayflies are easy to spot over rivers during summer. Look out for huge swarms of males rising and falling in their courtship dance during warm afternoons and evenings, especially from May to August.

Swarming is best seen on balmy, bright days, so when the weather's right, head to your nearest riverbank and settle in for one of nature’s greatest spectacles.

Did you know?

Mayflies are the only insects that moult as adults.

Threats and conservation

The greatest threat comes from pollution, including sewage, pesticides and heavy metals from industrial effluent, which can particularly affect nymphs. Even modest levels of pollution can have an effect, killing up to 80% of mayfly eggs before they hatch.

As a key part of the food chain, any pollution that impacts the nymphs also has repercussions for anything that relies on them for food, so can have a serious impact on the wider ecosystem.

More on woodland invertebrates