Most types of flies in San Diego County are nuisance pests. Rarely, some have the potential to cause allergic reactions, contaminate food, or spread disease.   

In some regions of the U.S. and around the world, flies can cause more serious diseases such as myiasis (botflies and screwworm flies), tularemia, dysentery, anthrax, and anaplasmosis. Almost all reported cases of these infections in San Diego County were contracted while visiting other countries.


  • House Fly (Summer): This fly is the most frequent pest to humans. The common house fly is grayish-black, about 1/4-inch-long, and covered in hair. In two weeks, one female fly may lay more than 1,000 eggs, typically in animal waste, household garbage, piled lawn clippings, or rotting fruit and vegetables.
  • Lesser House Fly (Cooler weather): The lesser house fly is seen flying around at eye level, hovering in the middle of a room, in a garage, on a patio, and under trees or other covered areas.  Larvae develop from eggs laid in moist organic matter.


Fly control and prevention is not difficult if done correctly. Flies breed in places where garbage, animal waste, and organic matter is found. 

  • Use garbage cans that have tight fitting lids and do not have holes
  • Wash the inside of garbage cans often
  • Throw away food and leftovers in plastic trash bags and tie them right away
  • Place grass clippings in plastic bags and tie up bags
  • Pick up animal droppings as soon as you can and tie in a plastic bag
  • Remove fallen fruit and vegetables right away

If you have dumpsters, it may be necessary to have trash picked up twice a week, especially at restaurants and apartment/condo complexes where there is a lot of trash.

If you have many adult flies around your property and cannot locate their breeding source, you can call the Vector Control Program for assistance.

Exclusion and Control


The best way to prevent fly problems is to remove their breeding sources but exclusion methods can help prevent flies from coming inside. To keep out flies, use screens with 16-gauge mesh. For smaller flies, such as fruit flies, use 24-gauge mesh screens. Keep any screens for windows and doors in good repair and free of gaps or holes.  Businesses may also want to:

  • Install self-closing doors
  • Install high-velocity fans over doors that must remain open


  • Fly strips and fly bags are effective and cheap and can be purchased at most grocery or home improvement stores
  • If needed, use insecticides and be sure to follow the instructions carefully
  • Fly swatters are effective for occasional flies


  (858) 694-2888



house fly photo by Axel Rouvin