Mayflies or Fishflies?

June 11, 2001

Tip Sheet: Mayflies

In the South, tortoises are referred to as gophers. Woodchucks and groundhogs are interchangeable terms in the Midwest, and, in Michigan, the insect that the rest of the country knows as the mayfly is called a fishfly.

According to entomologist Mark O’Brien of the University of Michigan Museum of Zoology, “Mayflies are really the correct term for the millions of Ephemeroptera that emerge from Lake Erie and other lakes. Even though the colloquial term may be ‘fishfly,’ it is erroneous. The term ‘fishfly’ actually names another entirely different group of insects, the Corydalidae, or dobson flies.”

For more information, contact O’Brien at (734) 647-2199 or

Improved Water Quality Signals Increase in Water Insects

“Larger numbers of mayflies are hatching than ever before,” says David Jude, research scientist for U-M’s Center for Great Lakes and Aquatic Sciences, and he cites the increase as “proof that water quality in Lake Erie has become much better.”

According to Jude, beginning in the 1940s “Lake Erie’s mayfly population became relatively nonexistent.” However, he adds, “in the past few years the water quality has improved tremendously, due to improved sewage treatment, and an unintended consequence of zebra mussels, which clear the water allowing more light penetration so harmful dissolved oxygen depletions no longer occur on the bottom. This healthier water also allows mayflies to flourish in bottom muds.”

“Before water quality seriously deteriorated in some areas of the country during the 1950-70s, huge numbers of mayflies emerged, requiring plows to remove them from bridges and beaches,” says Ethan Bright, graduate student in the U-M School of Natural Resources and Environment. “Now that water quality is improving, the insects are starting to appear in larger numbers again.” However, according to Bright, “populations of these are nowhere large enough where they may cause problems that require physical removal.”

For more information, contact Ethan Bright at or David Jude at (734) 763-3183 or

Mark O’Brienmfobrien@umich.eduDavid JudeEthan