If you have been anywhere near the Conestoga or Susquehanna Rivers in Pennsylvania this summer, or the Mississippi, Colorado, or other rivers, chances are that you have seen a mayfly or two thousand. The mayflies are thick and flying this summer, thanks to improved water quality.
“We had similar emergences 60 and 70 years ago, but then the pollution in our rivers caused the mayflies to decline,” explains Dr. John Wallace, entomologist at Millersville University. “Thanks to the Clean Water Act and decades of efforts to clean-up our waterways, we’ve been getting more and more mayflies.”
Wallace says there are three major groups of aquatic insects that indicate healthy water and a healthy environment; caddisflies, stoneflies and mayflies. “The more of those three types of insects you have in a stream system, the better the water quality,” says Wallace.
While individual mayflies are not harmful to people, they have caused a nuisance on bridges and in some areas when swarms of them can build up on roads and blanket cars. In nature, they are attracted to the reflection of the river when flying upstream to lay eggs, but, with increased development, they’re attracted to lights and can congregate in large numbers.
Wallace is overseeing a research project on the Wrightsville Bridge this summer. “We’re working with Wrightsville Borough in conducting a pilot study on the mass emergence of Hexagenia mayflies that occurred in mid/late June on the Susquehanna River. This applied research will hopefully provide baseline data to build upon in the upcoming years to better understand how to reduce the safety issues on the bridges when the mayflies are attracted to lights and die on the roadways. These data will hopefully help the Wrightsville and Columbia areas develop strategies for dealing with the swarms of mayflies in an environmentally safe manner. As a side project, we are collecting garbage bags of mayflies and freezing them for a class project in Ecology & Evolution this fall,” said Wallace. “For this project, we’ll use them in experiments to see if they are effective fertilizer for vegetable crops. We may soon be sweeping them into our flower beds as fertilizer.”
Mayflies only live about 24-48 hours and will be done emerging as adults by October. The current emergence or “hatch” of mayflies will likely be gone in a week or two, although there may be other species later this summer. Two factors that have led to their resurgence is that 1), They’re more prevalent in recent years because of the improved water quality and 2) the increase in suspended sediment loads in streams and rivers has increased suitable larval habitat for their burrowing larvae in the rivers.” says Wallace.
“We need to embrace the mayfly,” says Wallace, “or, at least put up with them. They’re good for feeding many organisms in both terrestrial and aquatic ecosystems, such as birds, bats, spiders and especially fish – all of which love to eat mayflies.”
While it hasn’t yet been discussed as a strategy for mayflies, entomophagy is the human use of insects as food. The eggs, larvae, pupae, and adults of certain insects have been eaten by humans from prehistoric times to the present day. While crickets and grasshoppers are among the most popular insects eaten around the world, Wallace says that with the concentration of protein in insects, who knows, someday we may be nibbling on mayflies.