Hind pair of
wings may be missing, or are much smaller than fore wings.
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".
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.
The nymphs are mainly herbivorous (some are carniverous 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.
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
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.
Mayfly nymphs (see the drawing of a nymph in the Caenidae family left and below) 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.
Acid rain has led to the loss of many populations in Northern Europe and America. The nymphs live in the mud or among water plants. Ephemerella sp. (left) are usually found creeping along the mud or on stream and river beds, and occasionally cover themselves with debris.
Ephemerella ignita can be found in a wide range of running waters, but rarely in still water.
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 the 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.
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.
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 left). 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 give them some camouflage. Nymphs are up to 12 mm long excluding the tail. Adults fly April - July.
Above 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.
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.
Right 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.
On the left 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 wing is 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.