River towns prepare for shad fly invasion

THOMSON — They sneak up on you. One day, you see one on your windshield. Later that night, you might see 20 or so flitting around a street light. The next day, they are swarming. The mayflies – affectionately referred to as shad flies – are coming on the upper Mississippi River.

Some years, the insects are so dense that state highway crews shut off the lights on the Savanna-Sabula Bridge. They have had to use snowplows in some areas to clear the road. Campers at Mississippi Palisades State Park sometimes seek help to get their can of pop out of the well-lit machine, clogged by shad flies.

What could be the makings of a very creepy science fiction film is brought down to earth by the U.S. Fish and Wildlife Service in its search for citizen scientists – observers along the Mississippi River to track the timing of the seasonal event of mayfly emergence.

Pam Steinhaus, visitor services manager at the Ingersoll Wetlands Learning Center in Thomson, said there will be a Mayfly Watch workshop from 9 to 11 a.m. June 20.

“This workshop will teach you everything that you need to know about becoming a successful citizen scientist, how to use nature’s notebook, and how to identify what you will be looking for,” she said.

This workshop is for all age groups and will be held at the center, 7071 Riverview Road in Thomson.

“There are usually several hatches throughout the summer, but generally the big hatch is in July,” Steinhaus said. “Water temperature plays a huge role on hatch times. Mayflies are very short lived, from 12 to 24 hours. When they hatch they do not have mouth parts, so their main function is breeding and laying eggs.”

Mayflies are an important food source for fish, especially during the summer emergence, but also throughout the year when they are in their larval form.

“When mayflies emerge from the Mississippi River, the result can be extraordinary! Large emergences can number in the millions – enough to be picked up by weather radar,” Steinhaus said. “Our hope is that our neighbors of the river, armed with their mayfly identification, will learn to notice the seasonal changes that occur on the river during the summer.

“They do make a mess, but it’s a great indicator of the health of our rivers.”

For more information about the workshop and to pre-register, call 815-273-2732.