Take a trip to the east side of Detroit and you will see them everywhere, adhered to walls like schools of dead fish, perfuming the air with their fishy odor.
Few things remind one so well of being in a particular place at a particular time as an insect invasion. If you see fish-flies, you are near water and it is June.
It could be worse; fish-flies neither sting nor bite, nor do they eat vegetation. They merely hover in great clouds around streetlights, their juicy bodies clinging in packs to the glass of lighted storefronts until they desiccate, or eventually carpet the streets so that a drive through St. Clair Shores or Grosse Pointe on a warm June evening with the windows rolled down will be filled with the soft music of their bodies crunching under the wheels.
For those interested in the science, fish-flies are in the genus Hexagenia of the order Ephemeroptera, the Mayflies. More science here and here (apparently the densities of Hexagenia in the Great Lakes are under threat- though you would never know it by visiting the east side of Detroit this past week).
Image Credit: http://www.lakestclairflyfishing.com/