The Ephemeroptera are thought to have evolved towards the end of the Carboniferous.
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.
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. (left) 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
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.
The Caenidae nymphs (see left and below) prefer muddy or sandy environments. The drawing below shows the typical body shape of nymphs in this family.
Ephemerella ignita (left) can be found in a wide range of running waters, but rarely in still water.