Most types of flies in San Diego County are primarily considered to be nuisance pests for humans.  Some may also have the potential to cause allergic reactions and contaminate food and people with bacteria and other diseases-causing agents.  These instances are rare.

In several regions around the country and the rest of the world, flies are also capable of causing more serious diseases such as myiasis (botflies and screwworm flies), tularemia, dysentery, anthrax and anaplasmosis.  Almost all reported cases in  San Diego County were discovered to be infections contracted when visiting other countries.

The fly that is most often a pest to humans is the house fly. The common house fly is grayish-black. It is about 1/4 inch long and is covered in hair. The female house fly is larger than the male. In two weeks, one female may lay more than 1,000 eggs in animal waste, household garbage and piled lawn clippings.

Common Flies

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

Fly Prevention
Fly control and prevention is not difficult as long as it is done correctly. Flies breed in places where garbage, animal waste and organic matter is found. Make sure you:

  • 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 up bags right away
  • Place grass clippings in plastic bags and tie up the bag
  • Pick up animal droppings as soon as you can and tie up in a plastic bag
  • Remove fallen fruit and vegetables right away; flies are attracted to sweet and sour smells

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 high volume of trash.

Fly Exclusion
Excluding flies from entering the home will help relieve their annoyance, but remember it is still important to remove their breeding sources. To keep out flies, use screens with 16 gauge mesh. In order to keep out smaller flies, such as fruit flies, 24 gauge mesh screens should be used.

  • Keep screens in good repair
  • Install self-closing doors
  • Install high velocity fans over doors that must remain open

Fly Control
Fly strips and fly bags are effective and a cheap way to control flies around the home. They can be purchased at most grocery and home improvement stores.

If you need to use insecticides to control flies in your home, make sure to follow the instructions carefully.

Fly swatters are still a good way to control the occasional fly. Keep one handy.

Fly Life Cycle

  • Embryo/Eggs: Females lay eggs in moist organic matter, such as garbage, animal waste or rotting fruits and vegetables.
  • Larvae: Eggs hatch into larvae, which have three stages and feed on the organic material.
  • Pupae: Larvae develop into pupae.
  • Adult: Adult flies hatch from pupae.

Call County Vector Control If:

  • You have a large amount of adult flies around your property and cannot locate their breeding source
  • You have questions about fly breeding around your property
  • You would like advice on how to prevent, exclude and control flies


For More Information On 
Flies Or Other Vectors Contact: 
(858) 694-2888  
 Vector Control Program