Garden Entomology - Royal Entomological Society

SPECIES PROFILE
Order : Ephemeroptera
MAYFLIES
Mayflies and dragonflies are the oldest surviving forms of flying insects. The ancestors of mayflies
first appeared in the Carboniferous period. Mayflies are typically found near freshwater streams
and rivers, into which they lay their eggs. Adults do not feed, and their role is restricted to mating
and laying eggs. This results in a brief adult life-span and is reflected by their formal scientific
name, Ephemeroptera. Indeed, one species of mayfly has an adult life so short that the males
survive for less than an hour. Mayflies can be seen in gardens near lotic (moving) freshwaters, so
people living near canals, streams and rivers may see large numbers. A few species do colonise
garden ponds, such as Cloeon dipterum, the pond olive. Mayfly nymphs are more hidden, foraging
for small particles of organic matter, such as algae, either filtered from the water or collected from
plants and rocks.
FACT FILE
• There are approximately 2,000
species of Emphemeroptera, and
they inhabit all continents, with
the exception of Antarctica. There
are 46 species found in the UK.
• Acid rain resulted in the loss of
many mayfly populations across
northern Europe and North
America.
• As with all insects, mayflies
develop through a series of
moults. During the penultimate
moult, their midgut is sealed at
both ends, and this fills with air,
causing the nymphs to float to the
surface. When this occurs in large
numbers, the effect is similar to
seeing rain falling on the water.
Mayfly Ephemera danica
Ephemera danica is the most common species of mayfly seen in the UK, where large mating swarms
can be seen on warm summer evenings near unpolluted slow-moving water bodies. Mating takes
place in the air. After mating, the female releases her eggs, which may number up to 8,000, into the
water. Both sexes die soon after reproducing. The eggs hatch and the life cycle generally takes two
years to complete, although in the warmer south of England the cycle may be completed in a year.
Species such as Ephemera danica are ecologically important as a food resource for many bird and
fish species. This important role as fish prey is recognised by fly-fishers, who have developed many
ingenious imitations of mayflies.