Millions of Visitors Invade Huron Overnight

Huron residents awoke to the invasion of millions of mayflies (Hexagenia limbata) this morning.  Apparently, the prevailing winds were just right to lead the insects into Huron.  Though the insects might seem bothersome, their presence is an indicator of a healthy Lake Erie.  In the early 1990s, no Hexagenia could be found in Lake Erie due to toxins in the sediments.  As the Lake has recovered from the abuse it suffered in the early part of the 20th century, so has the mayfly population.

Mayflies spend the majority of their life living deep in the sediments of lakes.  The mayflies

that you see covering the buildings of Huron are currently non-mating adults known as subimagos.  Over the next 24 to 48 hours, the mayflies will undergo their final molt and become adults.  You might notice their shed skins clinging to screens and other hard surfaces.  During this period, they do not eat-they do not even have mouth parts.  The only purpose of the adult stage of the mayfly’s life is to mate.  Once mating is complete, the adults die.

The females will lay their eggs in the water just after mating.  The eggs remain in the sediments until the spring when they hatch.  Once hatched, the mayfly is considered a nymph.  The nymphs will go through several life stages called instars.  They may experience as many as 30 instars that can take anywhere from 14 to 22 months.  During each instar, the mayfly sheds its skin or molts.  The nymphs breathe by moving their feathery gills, located along their abdomen, thus increasing the amount of water that passes over them and aiding in oxygen absorption.  The final nymphal instar swims to the surface and molts into a subimago.  Nymphal development time is temperature dependent, so development times vary.  In general, the emergence of the subimagos occurs during June and July. 

Mayfly nymph

Living near the shores of Lake Erie has many benefits.  It is up to you whether you deem the emergence of the mayflies as one of these benefits!  Frankly, I think they are a beautiful insect, though the numbers in which we are seeing the mayflies today is a bit overwhelming.  Remember, the mayflies will only remain here for a short time, so we will be free of them soon or at least until the next hatch.