Swarms of small flies can be a common sight during late afternoons and evenings in September and October. The insects involved superficially look similar to mosquitoes and often are about the same size. However, they are instead a type of non-biting midge, members of the family Chironomidae.

What attracts attention are the towering mating swarms that many midges produce. These form over some prominent point or conspicuous, usually light-colored object. This may include automobiles, a piece of lawn or porch furniture, or even a human. These mating swarms are made up almost entirely of the males. When the wingbeat frequency of approaching females is detected, a few will dart out to meet and mate with her. Because of the sensitivity of the swarming males to sound you can often see erratic changes in the swarm pattern in response to sounds such as a handclap or even spoken word.