The Ephemeridae is a family of insects belonging to the order Ephemeroptera, with around 200 described species in Europe. A natural wonder, Ephemeroptera spend most of their lives underwater, during their larval stage. Aquatic biotopes are therefore key to their survival, and Lake Geneva and its tributaries offer them prime habitats.
The larvae live between 6 months and 2 years underwater, in the silt of lakes, streams or marshes. They can be recognised by their characteristic cerci (spikes at the bottom of the abdomen) and their gills, which enable them to breathe underwater. They feed mainly on algae residues on rocks. Mayfly larvae are important bio-indicators. Scientific studies show considerable negative impacts on populations, even at very low pollution thresholds (pesticides, oil). Their presence therefore indicates good water quality.
During its life, the larva will moult around ten times before reaching the adult stage and being able to leave the water to reproduce. During the last moult, it loses the ability to feed itself because its mandibles atrophy, drastically reducing its life expectancy. As soon as they emerge from the water in spring, these ephemeral insects metamorphose into winged adults, but they will only live for a few hours to a maximum of two days. In this final stage, mayflies are very sensitive to light pollution and are attracted by the lights of our activities.
Their reproduction is also remarkable: the winged males gather in their thousands so that the females can identify them. First, the male performs a nuptial dance to attract a female for mating in the air. The female then returns to the water to lay her eggs. Finally, the two adults die quickly after reproducing.
Photo credits: © Nick Goodrum / Flickr
