Friday, June 28, 2013

Mayfly Hatch

The mayflies (Ephemeroptera) are out.  I was watching them the other night by the lake.  They have recently hatched after spending their young lives under water as nymphs.  When they first come to the surface, they have wings but do not fly yet, they are commonly called duns by fishermen, this is their subimago state.  They shed one last time and can use their wings to fly,  the imago state, which means they are ready to mate.   Mayfly nymphs have gills to breath under water, and can take up to a year to go through what is called incomplete metamorphosis as they molt their exoskeletons.  This may happen 20-40 times depending on the species.

These episodes of life stages are called instars.  After the last instar, they climb out of the water and rest until they complete their final molt and begin to fly.  At this last stage of their life they do not have mouth parts, their only purpose is to mate.  They do this in a courtship dance above the water.

The males swing up and down in the air, looking for a mate.

I saw several mating in the air, clinging to each other in flight.  After this ritual, the males go off to the nearest tree limb, lamppost or rock and die.  The females go to the water to lay their eggs and then die on the surface.  On the lake it looks like a soft rain is falling when you watch hundreds of the female mayflies dipping their bottoms where the eggs are stored, into the water.

Mayflies need clean, well oxygenated water to survive their youth.  You find them around lakes and streams where the water is not polluted.  They thrive around Skaneateles Lake and are a treasure to see each year.