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Mayflies

Tabs group

Depending on the species, mayflies range from 2 to 18 mm in length, excluding the antennae and caudal filaments. They are often whitish or yellowish in colour.

Mayflies have vestigial mouthparts and are therefore unable to feed. The membranous and extensively veined wings are held vertically when at rest.

Mayflies have two to three long filaments at the tip of the abdomen. These have a tactile role, stabilize the insect’s flight and, together with the wings, help prevent joined mating couples from falling to the ground.

Life cycle

The larva, sometimes also called nymph or naiad, is aquatic. Larvae breathe through abdominal gills. Their body shape varies according to species. Some are swimmers, some crawl through muddy bottoms, others are burrowers, and yet others live in fast-flowing streams and rivers.

Larvae undergo 12 to 20 moults before reaching their full adult form; depending on the species, this can take anywhere from one to three years. Larvae float to the surface when they moult for the last time. They appear as colourless insects with wings edged with hairs: this is the subimago, or pre-adult stage. They fly to rest on nearby vegetation. Some twenty hours later in a final moult called the imaginal moult, the fully mature adult, or imago, emerges. Their short lifespan, lasting only a few hours or days, is devoted essentially to mating and egg laying.

After mating in full flight, females lay several hundred eggs on the surface of lakes and streams. The eggs then sink and attach themselves to the bottom. The embryonic stage usually lasts a few weeks, but it can be interrupted by winter hibernation (diapause). Males die after mating and females after laying the eggs.

French name

Éphémères (mouches de mai, mannes)

English name

Mayflies

Class

Insecta

Order

Ephemeroptera

Habitat/Diet

Habitat

Mayflies spend most of their life cycle in the water, in either egg or larval form. They abound in many non-polluted water environments. Adults are frequently seen near ponds, lakes, rivers and streams.

Did you know?

Interesting facts

The mass emergence of mayflies, especially common in late June and early July, can be an impressive sight. Some people living near the water find the swarms of insects bothersome and messy, given the heaps of dead adults and subimago exuviae that remain.

Most artificial flies used by Quebec anglers resemble mayflies. Fly fishermen create lures that replicate the insect at each stage in its development, to match the appropriate seasons.

Ecological roles

This group of insects is a vital link in the food chain of freshwater ecosystems, between plants and secondary consumers (especially fish). The larvae are eaten by other aquatic insects, leeches, crayfish and amphibians. Dragonflies, birds and bats eat adult mayflies.

Mayflies are useful environmental indicators. Aquatic larvae of many species are sensitive to pollution to different degrees. An abundance of mayflies is a sign of good water quality.