MAYFLIES

Mayflies are aquatic insects belonging to the order Ephemeroptera. This order is part of an ancient group of insects termed the Palaeoptera, which also contains dragonflies and damselflies. Over 3,000 species of mayfly are known worldwide, grouped into over 400 genera in 42 families.

Mayflies are distributed all over the world in clean freshwater habitats, though absent from Antarctica. Mayfly is the common name for small, fragile, soft-bodied insects comprising the order Ephemeroptera (from Greek ephemeros, meaning, living a day, and ptera, wings).

Mayflies exhibit a number of ancestral traits that were probably present in the first flying insects, such as long tails and wings that do not fold flat over the abdomen. Their immature stages are aquatic fresh water forms, whose presence indicates a clean, unpolluted environment. They are unique among insect orders in having a fully winged terrestrial preadult stage, the subimago, which moults into a sexually mature adult, the imago.

Adult mayflies, or imagos, are relatively primitive in structure, exhibiting traits that were probably present in the first flying insects. These include long tails and wings that do not fold flat over the abdomen. Mayflies are delicate-looking insects with one or two pairs of membranous, triangular wings, which are extensively covered with veins.

Immature mayflies are aquatic and are referred to as nymphs or naiads. In contrast to their short lives as adults, they may live for several years in the water. Mayfly nymphs feed on algae and organic waste, and a few are predatory. Nymphs play an important role in cleaning streams, as they consume contaminants and then later, as adults, carry them to land where they can safely degrade over time.

Mayflies are specially adapted for reproduction, as no energy is wasted on body parts other than those needed to reproduce: adults have reduced, non-functioning mouthparts, as they do not feed, and many species also have reduced legs (except for the elongate male forelegs which are used during mating). Mayflies spend their entire adult lives in flight seeking a mate.

Often, all the mayflies in a population mature at once (a hatch), and for a day or two in the spring or autumn, mayflies are everywhere, dancing around each other in large groups, or resting on every available surface. In many species the emergence is synchronised with dawn or dusk, and light intensity seems to be an important cue for emergence, but other factors may also be involved.

Each insect has a characteristic up-and-down pattern of movement; strong wingbeats propel it upwards and forwards with the tail sloping down; when it stops moving its wings, it falls passively with the abdomen tilted upwards.

Females typically lay between four hundred and three thousand eggs.