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Swarming Midges

By Whitney Cranshaw, Colorado State University Cooperative Extension, Entomology

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.

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Chironomid midges develop in moist soil, lakes and slow moving rivers. The larvae scavenge decaying organic matter, feed on algae and other phytoplankton and the midges themselves can be an important part of the diet of fish. Although adults may emerge and be found during almost any time during the warmer seasons, emergences are often fairly synchronized, apparently being triggered by changes in weather patterns.

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.

Photos: Judy Sedbrook

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Date last revised: 01/05/2010