In July 1957, Hastings Minnesota was invaded by fish flies. Millions of them. So many that they piled up on roads in enormous drifts and prevented cars from getting through.
From the History of Hastings blog
The cops were called. The Fire Department was called. State highway sanders were useless against the combined efforts of the millions of fish flies who piled up their little bodies against all human efforts. Meanwhile the deck of the bridge became as slippery and slimy as grease, stalling cars that had to be moved to release the motorists stalled and steaming in cars with all windows closed against the bugs.
For over an hour a group of strong-backed youths, who volunteered their help, pushed and tugged cars through the 2 1/2 ft. bug-drift in the center of the bridge. Some were members of the very commendable teenager Cavalier Auto Club, supported by the Greater Hastings Association. The young men did a terrific job, some wearing bathing trunks, as they waded through the piles of bugs to help motorists. They pushed, advised, sweated with flies in ears, mouths, eyes. Look at those spots in front of the camera lens. They’re bugs…. stacked up on the car hood, piled up in drifts. How prolific-the hatch was terrific.