Spring's Mayflies are a Good Sign

Recently, some mayflies once again appeared in Lake Erie’s western basin. Sometimes called Canadian soldiers, shad flies, fish flies, or June bugs, these harmless insects are official known to scientists as Hexagenia. They live most of their lives in burrows in Lake Erie’s soft bottom. From late May to late August, whenever the water temperature is just right, they emerge, molt, swarm, mate, lay eggs, and die - all within 48 hours!

Their reappearance signals a healthier Lake Erie. While it’s great for the perch and channel catfish, it’s not so great for tourism. In fact, the size of the hatch in June 1996 caught residents of Port Clinton and other shoreline communities off guard. Suddenly mayflies were everywhere - covering everything! Picnic tables, cars, boats, porches, docks, sidewalks, and streets were piled high with them.

Attracted to bright lights, mayflies swarmed at an electrical substation near Lake Erie. They were so numerous that they began conducting electricity across insulators, causing brownouts throughout Northwest Ohio. When streets became dangerously slick with their smelly little carcasses, city workers posted warning signs, then rolled out the plows and scooped up 38 dump-truck loads!

The hatch of 1996 may have seemed large, but it was small when compared to the hatch that occurred on the evening of July 22, 1951. The following morning biologists at the Stone Laboratory on Gibraltar Island began making some calculations. They rated the density of mayflies on lawns at Put-in-Bay as 2,650 mayflies per square foot. Twelve bushels, weighing 38 pounds each, were scooped up from behind a single window of the laboratory. One pound was found to contain 8,100 mayflies. Therefore, the single pile was estimated to contain 2,380,000 mayflies. According to Dr. Thomas H. Langlois’ report, much larger swarms had accumulated around two lampposts on Middle Bass Island on the same night. He estimated conservatively that two tons or 32,400,000 mayflies lay under each lamp post! This quantity had emerged from only 50 acres of Lake Erie’s bottom.

Franz Theodore Stone Laboratory
Gibraltar Island, Lake Erie

The following year, mayflies met with disaster. By the mid-60s, they had disappeared from Lake Erie. Excessive algae growth resulting from high levels of phosphorous in the water hastened the rate of decay, consuming so much oxygen at the lake bottom that the mayflies could not survive. Little did we know that the ever-present green scum and rotting masses of algae could virtually destroy tons and tons of mayflies that had been part of Lake Erie’s ecosystem for thousands of years. So, when those pesky mayflies descend, TRY to give thanks for a healthy Lake Erie.