Common Flies in Alameda County

Blue and black blow flies are related to the green bottle fly. The blue blow fly, also known as the common blow fly, proliferates in warmer months of the year and breeds in the carcasses of dead animals. The black blow fly is more abundant during cooler months and has larval sites similar to the green bottle fly, but takes longer to develop. Sometimes blue blow flies may breed indoors if there is a dead animal inside of a structure. If you are experiencing these flies in your home, inspect the basement, crawl spaces and attic for dead animals (rats, birds, raccoons, skunks, cats).

These small flies commonly fly around and land on walls in kitchen and bathroom areas, and floor drains. Larvae feed on anything that ferments such as ripe/rotten fruits, damp flour, residue in soda and beer cans, and potato skins. Locate and remove larval food sources to effectively eliminate the fly problem. Remove recycled cans and bottles regularly.

Small flies with pointed “hairy-looking” wings. They rest on walls or ceilings of bathrooms or kitchens. This fly breeds in rich organic matter usually originating from a plumbing or sewage leak. Also breeds in slime accumulations in drains. Repair plumbing leaks and clean drains with a brush and enzymatic type drain cleaner to prevent drain fly outbreaks.

Swarms of flies hovering under porches, patios and other shaded areas are usually the lesser house fly. They often fly in an irregular back and forth pattern. Primary larval food sources are lawn clippings, compost, bird manure (roosting pigeons), or other moist organic sources. Pesticide applications to swarms or on walls around swarm site may give temporary control. Fly traps are not effective for this fly; the most effective tactic is to tightly cover or eliminate larval sources.

The house fly is one of the most common flies in the world. Larvae breed in landfill sites, rotting compost, and animal manure. Adult flies cease activity in the fall and seek overwintering sites where they remain inactive for the winter. These flies can also be found in rural areas with livestock and animal manure buildup. Elimination or treatment of larval sources is the best control method, but exclusion with screens on windows and doors may be the only solution.

This robust black fly has a painful bite. The larvae feed in damp, highly organic materials such as moist hay and droppings. Occasionally this fly can become a problem in dairy farms and other rural settings with livestock.

This is a very small “no-see-um” gnat that has a very painful bite. It breeds in a specific soil type found in and around the Pleasanton area of the county. Due to the development of new housing in this area, this fly is rarely encountered.

The non-biting fungus gnat breeds in over-watered plant soils and may become a nuisance. Replacing potted soil or drying out soil will help reduce numbers.

Some flies will overwinter in large numbers in homes; usually in attic or wall voids. Many flies may enter the living area and cause a considerable nuisance. The Cluster Fly (Pollenia rudis) which feeds on earthworms will utilize homes to overwinter. The Face Fly (Musca autumalis) which is similar in appearance to the House fly will also overwinter within homes. Pesticide applications can be used to kill existing flies for temporary control. Sealing all exterior cracks and openings is highly recommended for preventing future infestations.