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The mayfly’s lifecycle: a fascinating, fleeting story

May 16, 2011

© John Slader Mayfly. Commended Riverfly Partnership / National Insect Week 2010

Guest author: Craig Macadam, Riverflies partnership, Buglife and Ephemeroptera Recording Scheme

The mayfly’s lifecycle is one of the most fascinating and fleeting stories in the natural world.  One of the many characteristics that makes mayflies the unique insects they are is the potential for two different winged adult forms in their life cycle. The nymph emerges from the water as a dull-coloured sub-imago (or dun) that seeks shelter in bankside vegetation and trees. After a period of a couple of hours or more, the sub-imago once again 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 lifecycle, however it is thought that they may not be able to achieve the change from nymph to sexually mature adult in one step.

A mayfly’s life cycle starts with the males forming a swarm above the water and the females flying into the swarm 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 to lie motionless, with her wings flat on the surface, where fish pick them off at their leisure. The male fly rarely returns to the water but instead he goes off to die on the nearby land.

The eggs fall to the bottom of the water where they stick to plants and stones. Flies of the Mayfly family Baetidae pull themselves under the water to attach their eggs directly to the bed before being drowned by the current. The nymphs take anything between a few days to a number of weeks to hatch depending on water conditions and the species, and the resultant nymphs will spend various lengths of time, up to two years, foraging on the bottom before emerging as an adult fly.

When 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. While they rest here to dry their newly exposed wings, they are at their most vulnerable to attack from fish.

Some species exhibit great synchronicity in their hatching.  The North American species Hexagenia limbata hatches in huge numbers from the Mississippi every year.  The total number of mayflies in this hatch are estimated to be around 18 trillion – more than 3,000 times the number of people on earth.  The newly emerged insects are attracted to lights in riverside towns and villages and the local authorities deploy snow clearing vehicle to remove their rotting corpses.  Ironically, what is seen as a nuisance in America is seen as a gift in Africa.  Locals around Lake Victoria gather adults of the mayfly Povilla adusta together with Chironomid midges to make a type of patty called ‘Kungu’.  This protein rich food stuff is an important part of their diet.

14 Comments leave one →
  1. October 11, 2012 18:09

    Very interesting.

  2. December 26, 2012 02:36

    Very nice, very comprehensive. Thnx for sharing.

  3. December 28, 2012 06:34

    It’s really a great and helpful piece of info. I’m glad that you simply shared this helpful information with us. Please keep us informed like this. Thank you for sharing.

  4. July 10, 2013 22:19

    I seem to have them in my garden suddenly today and I can confirm that they die very quickly so when you touch them they just float down to the ground …

  5. July 8, 2014 19:53

    For an interesting take on the mayflies lifecycle, see ‘the fairy’s foxtrot’ in Natures Secret Adventures. Great for teaching kids

  6. charles Salekin permalink
    August 15, 2014 18:08

    Thanks for that explanation! I was just wondering myself why the extra set of wings, as I’d noted them flying from the river to the land, only to split open and evolve another set of wings.

  7. Tim Crumpler permalink
    March 16, 2016 16:59

    why do mayflies drop their eggs in water. Is it a defense mechanism for the eggs or what?

  8. PLM permalink
    July 15, 2016 18:00

    What time of the year are they the most prevalent? I’m having problems with them this summer, June-July so far.

  9. Linda permalink
    July 27, 2016 14:33

    Can mayflies get through the screens? We have tons of them that got into the house.

  10. PLM permalink
    August 4, 2016 17:25

    Thank you so much. I’ve only lived in this area a couple of years and had no idea what these insects were. Now I know I can’t open my windows because they get through.


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