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Nuisance Flies

What are nuisance flies?
Nuisance flies are insects that are annoying or can spread diseases to people and domestic animals by biting or carrying disease causing pathogens. All nuisance flies are members of the Insect Order "Diptera" (meaning "two-wings"). The adults can be identified by having only one pair of wings but can look very different from one another. Nuisance flies are found throughout California and cause a variety of problems. The immature (larval) stages of these flies are found in different habitats, including water and semi-aquatic sites. Fly larvae found in decaying organic matter are sometimes called maggots.

What is the public health importance of nuisance flies?
These insects are attracted to dead animals, feces, and garbage, allowing them to spread a variety of disease-causing bacteria and parasites. Some flies are capable of delivering painful bites and can transmit diseases to humans and animals. Other nuisance flies reproduce quickly and are annoying simply because of their numbers.

How are nuisance flies controlled?
The term "nuisance flies" covers many species so there is no one method of control. Suggested steps include the following:
  • Identify the problem fly, if possible, by using online resources, pictorial guides or by contacting local environmental health departments, vector control agencies or university extension services.
  • Eliminate items that attract flies such as rotting organic material (meat, leaves or grass clippings, household garbage) or animal feces.
  • Be sure that windows and doors close properly and that screens are in good repair.
  • Use insect repellents containing the active ingredient DEET, picaridin, oil of lemon eucalyptus, or IR3535. Wear long sleeved shirts and long pants to provide an effective barrier against biting flies.
  • Turn off or limit the use of lights at night to discourage those flies that are attracted to light.
  • Cover food, whether for humans or animals.
  • Various traps, baits, and insecticidal sprays are available for fly control. Read the product labels or consult a pest control professional to determine which products are available to control the specific nuisance fly problem. ​​

Generally, nuisance flies are more common in spring, summer, and fall, but many are active during the winter months. Due to California's range of habitats and elevations, the occurrence of nuisance flies varies by region.

Common nuisance flies include the following:


Black flies (Simuliidae) are also known as buffalo gnats because of the humpbacked appearance of the adults.  They are biting flies and are commonly found along waterways and in shaded forests. In California, black flies do not transmit human disease. ​​


Blow flies (Calliphoridae) are mostly large, metallic flies. They breed in garbage, dead animals, and human food. These insects invade homes and can transmit bacterial and viral diseases. To reduce the numbers of these flies, remove the materials they are attracted to like dead animals and feces. 

Image used with permission. Copyright © 2008 Gayle Strickland


 Canyon flies (Muscidae) are actually a complex of nine closely related species. They are much more common in southern California than in northern California. Adult canyon flies feed on sweat, mucous, tears, and other bodily discharges. These flies do not bite, but instead will crawl about the body to feed. These flies are thought to transmit the rare mammalian eye worm Thelazia californiensis to humans and other animals.

Image used with permission by Alec Gerry at UC-Riverside


Flesh flies (Sarcophagidae) are unusual among nuisance flies because the females deposit live larvae instead of eggs. Like blow flies, flesh flies are attracted to garbage, feces, rotting flesh, and human food. The immediate removal of food sources will reduce flesh fly numbers.​ 

Image used with permission. Copyright © 2008 Ted Kropiewnicki


Horse and deer flies (Tabanidae) are commonly found in forests near lakes, rivers, and streams. They are large flies capable of delivering painful bites.

Image used with permission. Copyright © 2017 Stephen Luk


House flies (Muscidae: Musca domestica) are perhaps the most common of all flies encountered indoors, but they are also abundant outdoors. House flies will breed in feces, garbage, or other rotting organic material. Removing these breeding sources will reduce house fly numbers. They are attracted to fruits and other sugary foods. House flies are capable of spreading bacterial and viral diseases.

Image courtesy of University of Florida


Midges (Chironomidae) look like mosquitoes but do not bite. They are attracted to lights and can be present in large numbers. They have aquatic larvae and the adults are more common around bodies of water. Midges do not transmit human disease, but in rare cases, may cause asthmatic reactions in some people who are frequently exposed to large numbers of these flies.

Image used with permission. Copyright © 2010 Steven Nanz


No-see-ums (Ceratopogonidae) are tiny flies, the smallest being one millimeter in length. In California, no-see-ums do not transmit human disease but cause very painful bites that can itch for days.​ ​​​​ 

Image used with permission. Copyright © 2005 Kerry S. Matz

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