Ephemeroptera (mayflies)

Fast facts about Ephemeroptera (mayflies)

  • Hind pair of wings may be missing, or are much smaller than fore wings.
  • Wings held sideways at rest, they cannot be folded over the abdomen
  • Adults do not feed.
  • Adult mouthparts are either missing or reduced.
  • Adult male legs modified for grasping female during mating flight.
  • Mayflies are the only insects that moult after attaining the winged state.
  • Antennae minute in adults.
  • 2 or 3 terminal abdominal filaments in adults, 3 in nymphs.
  • Nymphs aquatic and long lived, 3-4 years in some cases.
  • Often called "the most primitive insects with wings".
  • Oldes existing order of winged insects.
  • Many of the common species were given their names by anglers.
  • They have a low tolerance of pollution, so the presence/absence of the nymphs is often used in the assessment of water quality.
  • About 3100 species worldwide, 330 in Europe, 51 in British Isles.

The Ephemeroptera are thought to have evolved towards the end of the Carboniferous.

Mayfly nymphs

Mayfly nymphs are mainly herbivorous (some are carnivorous or even cannibalistic) feeding off algae and plant debris. They breathe though a series of tracheal gills, usually seven pairs, growing out of the side of their abdomen - see the drawings below.

Epemerella ignita nymph, may fly nymph

Mayfly nymphs spend their lives in water, usually preferring clean water, so are rarely found in polluted waterways. So their presence is usually an indicator of relatively unpolluted water. The nymphs live in the mud or among water plants. Ephemerella sp. (above) are usually found creeping along the mud or on stream and river beds, and occasionally cover themselves with debris.

Development to adult state can take as long as two years in colder regions, but only a few months in warmer areas. During this time the nymph can go through as many as 45 moults (Stenacron interpunctatum canadense)!

During the final instar the nymph will stop feeding for a while, then climb out of the water or float to the surface. Then within a few seconds the skin splits and the insect emerges in its final nymphal stage and flies off.

Mayflies are the only insects that have fully functional wings before they reach adulthood. Within a few hours, or in some species minutes, this nymphal skin is also moulted and the insect emerges as a full adult.

Acid rain has led to the loss of many populations in Northern Europe and America.

Adult mayflies

Adult mayfly

Adult mayflies do not live very long, some just for a few hours while others can hang around for a few days. Dolania americana lives for less than five minutes after her final molt. During those five minutes she chooses a mate, mates, and lays her eggs.

Mayflies are weak fliers, so rarely stray far from water unless the wind carries them. Their whole purpose as adults is to mate. Some of them have no mouthparts, and even those that do do not feed. Usually a large number of adults emerge in a synchronized hatch. The mass emergence of mayflies is actually a defence mechanism as the predators, mainly fish, bats and birds, are unable to eat them all, so many mayflies escape predation, and go on to breed.

Mayfly mating

Mating swarms are most common in the late afternoon. Males dance to attract the attention of females. The attraction seems wholly visible as no pheromone has yet been discovered. The female flies into a swarm of males. A male grabs her, and mating proceeds.

Mayflies mate on the wing. After mating the female drops eggs into the water, though some species actually go underwater to lay the eggs on plants. A single female can produce thousands of eggs.

After this the adults usually flop into the water where they are the beloved food of fishes, something well known to anglers.

Caenidae family

The Caenidae nymphs (see above left and below) prefer muddy or sandy environments. The drawing below shows the typical body shape of nymphs in this family.

Ephemerella ignita (above) can be found in a wide range of running waters, but rarely in still water.

mayfly nymph, Caenidae family

Leptophlebiidae Family

Paraleptophlebia submarginata nymph

There are 6 British species in this family. In the Leptophlebiidea the nymphs often have tails as long as or longer then their body, and the tail filaments are usually held quite widely apart (see above). They tend to crawl around in silt or live in burrows and cavities, and are not very good swimmers.

Left is the nymph of Paraleptophlebia submarginata, also known as the Turkey Brown. Note that the gills are split into 2 blades. These nymphs are not very good swimmers and tend to lurk in vegetation or on dead leaves, which gives them some camouflage. Nymphs are up to 12 mm long excluding the tail. Adults fly April - July.

Below is the nymph Habrophlebia fusca, and has the common name Ditch dun. Its body length can reach 8 mm, so it is quite small. It is usually found in small, slow flowing streams and weed choked ditches.

Habrophlebia fusca, nymph, may fly nymph

Heptageniidae family

There are 11 British species in this family. Nymphs in this family are known as stone clingers. The typical nymph body shape is flat, broad and fat with strong legs. The eyes are located on the top of the head. As the common name for the family suggests, they are found in fast flowing waters clinging on to stones.

Ecdyonurus sp., nymph, may fly nymph

Above is the nymph Ecdyonurus sp. Note that it is broad and flat with large, flat legs. It is usually found in fast flowing water and lake edges.

Baetidae family, the Olives

There are 14 British species in this family. Nymphs in this family are usually slender and good swimmers.

Below is the nymph of Centroptilum leutolum, which has the common name of Small spurwing. The nymphal body length reaches 9 mm, and it is found in slow, weedy calcareous rivers and shallow weedy lakes.

The adult has 2 tails, and the hind wings are reduced to a thin, pointed spur - hence the common name. Adults can be seen as early a April, and as late as November, but are more commonly seen from June - September.

Centroptilum leutolum nymph Smith, L. (2014). Characteristics of the insect orders. Amazon. Characteristics of the insect orders with drawings and photographs to help you understand the differences between the different types of insect, and identify which order an insect is in, as well as fast facts about each insect order, and links to web pages with more detailed information. Many orders have separate sections about the life cycle of the insect as well as its habitat requirements, and fossil history.
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