Mayfly Life Cycle
Mayfly Life Cycle – OverviewThe mayfly life cycle is one of the most fascinating and fleeting stories in the natural world. One of the many characteristics that makes mayflies unique is the two distinct winged adult stages of their life cycle. The nymph emerges from the water as a dull-coloured sub-imago (or dun) that seeks shelter on bankside vegetation. After a period of a couple of hours or more, the dun sheds its skin to transform into the brightly coloured imago (or spinner). It is not clear why mayflies have retained this unique step in their life cycle, however it is thought that they may not be able to achieve the change from nymph to sexually mature adult in one step. During the adult stage, mayflies do not eat, this is another unique characteristic of the mayfly.
Mayfly Life Cycle – Spinner MatingMayfly mating starts with the male spinners forming a swarm above the water and the females joining the swarm in order to mate. The male grabs a passing female with its elongated front legs and the pair mate in flight. After copulation, the male releases the female, which then descends to the surface of the water where she lays her eggs. Once mated she will fall, spent, onto the water surface and die, with her wings flat on the surface, where fish pick them off at their leisure. Males will eventually die as well either falling in the water or dying nearby.
Mayfly Life Cycle – NymphThe eggs fall to the bottom of the water where they stick to plants and stones. They will hatch anywhere between a few days to a few weeks depending on the water conditions and the species.
The nymphs will then spend ~one year foraging on the bottom before emerging as an adult fly.
Mayfly Life Cycle – EmergerWhen it is time to emerge, the nymphs make their way to the surface where they pull themselves free of their nymphal shuck and emerge as a sub-imago or dun. While they rest here to dry their newly exposed wings, they are at their most vulnerable to attack from fish.
The duns that don’t get eaten by the trout quickly fly up to nearby vegetation and morph into spinners within a few hours and the cycle resumes.