Good News From Mayflies

Return of the Hexagenia mayfly is a sign of Lake Erie's ecological recovery

  • NWF Staff
  • Oct 01, 1998
For the last three years, a species of mayfly called Hexagenia has plagued towns along the western basin of Lake Erie in springtime. Swarms of the winged creatures have made roads slick after being squashed by cars and have flown into peoples´ clothes and mouths. A huge cloud of the insects even caused a brownout in northwestern Ohio after being attracted to the lights of an electrical substation and conducting electricity across insulators.
Believe it or not, aside from the inconvenience, all of that is good news--not just in spring but year-round. That is because the reappearance of Hexagenia is a sign the region is regaining a level of ecological health it has not experienced for almost half a century. The mayfly virtually disappeared from Lake Erie--as well as several other heavily populated Great Lakes locations and the upper Mississippi River--by the late 1950s, victim in part of algal blooms and decomposing sewage that robbed the lake bed of oxygen. Now the insect is showing up in many of those sites again, as well as thriving in Lake Erie.

Hexegenia nymphs live in the sediment of relatively shallow water--as deep as 40 or 50 feet--emerging at the end of two years for a single day or two of flight. No longer able to eat at that point in their life cycle, the winged creatures´ only goal is to reproduce. For females, that not only means mating but also laying fertilized eggs on the surface of water. And that is part of the reason for the traffic problems associated with mayflies: A new study from Hungary reveals that when asphalt reflects light, mayflies lay their eggs on roads, presumably mistaking the surface for water.

Mayfly nymphs were once an important part of the aquatic and near-shore food web, and scientists have hope that the insect once again will dependably nourish fish and birds near the populated areas where it did so before.

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