The Riverfly 8 ….. key invertebrates which indicate the ecological health of the river.

The RLA Riverfly team monitor 7 sites on the river every month to detect and count these species. That site gets a score which is then updated onto the national Riverfly Partnership Cartographer. 

Introducing #2 The Mayfly!

Meanwhile …… 300 million years ago, way before dinosaurs appeared, there were these flying insects of the order Ephemeroptera meaning “short lived with wings” in Greek.

“Not so fast!” these Mayflies might say, “We may appear to be short lived in our adult form but our life cycle is far from ephemeral!” 

Hatching from eggs, they spend most of their lives as the larvae us Riverfly monitors love to find.  They may well live in this larval form for up to TWO YEARS shedding their skin repeatedly as they grow.  

Metamorphosis as found in frogs and butterflies is well known but Mayflies are hemimetabolous.  

Some may describe this as incomplete metamorphosis but this sounds pretty disrespectful towards such an ancient critter! It means that they have no pupal stage and are the only group of insects with two winged stages in their life cycle.

Enter Stage One …. the pre adult Subimago or Dun.

When the time is right, and not always in May, this Dun will emerge from its larval form. Gas and air accumulates underneath the exoskeleton to help it rise up to the surface of the water where it struggles free of the nymphal shuck. Once safe on land, it can now breathe again, pump fluid into the veins in its wings which now dry and enable it to fly. Many don’t make it this far and are easy meals for other river inhabitants. 

For the survivors, a few hours or perhaps only minutes later…

Enter Stage Two … the adult Imago or Spinner. 

When the time is right, this Spinner moults from the Dun like a Russian doll, ready for action and procreation! There is no time to waste as the Subimago and Imago run on larval food reserves and cannot top up, having vestigial mouthparts and a digestive system full of air! The Spinners often emerge in synchrony, the females releasing a scent to attract the males which form a swarm just above the water and the females fly into the mêlée, mating on the wing.  

Now this IS the short lived part ….

The females then fall onto the surface of the water, lay their eggs …. and die! After their burst of action, the males fly off to nearby land, sometimes after having taken a little drink …. and die!

Fortuitous then that they lay between 400 and 3000 eggs to increase the chance that more offspring will survive. Other adaptations to cover themselves are that they have paired genitalia.  

Yes, you read that correctly!

The male has two penises and the female two gonopores.  As time is of the essence, both are used simultaneously to ensure quick sperm transfer and immediate fertilisation of the eggs!

Yes, you read that correctly.  

Double or quits!

And talk about belt and braces, if the males don’t turn up, some females can produce viable female offspring: parthenogenesis!

Long Live the Mayfly for another 300 million years as long as we keep our rivers clear and clean!