Nuisance Flies 

Fruit fly – aka vinegar fly

There are several species of vinegar or pomice flies native to the PNW in addition to the invasive spotted wing drosophila.

Fruit flies can be a problem year round, but are especially common during late summer/fall because they are attracted to ripened or fermenting fruits and vegetables. Tomatoes, melons, squash, grapes and other perishable items brought in from the garden are often the cause of an infestation developing indoors. Fruit flies are also attracted to rotting bananas, potatoes, onions and other unrefrigerated produce purchased at the grocery store. 



Biology: Adults are about 1/8 inch long and usually have red eyes. The front portion of the body is tan and the rear portion is black. Fruit flies lay their eggs near the surface of fermenting foods or other moist, organic materials. Upon emerging, the tiny larvae continue to feed near the surface of the fermenting mass. This surface-feeding characteristic of the larvae is significant in that damaged or over-ripened portions of fruits and vegetables can be cut away without having to discard the remainder for fear of retaining any developing larvae. The reproductive potential of fruit flies is enormous; given the opportunity, they will lay about 500 eggs. The entire lifecycle from egg to adult can be completed in about a week. 

Prevention: The best way to avoid problems with fruit flies is to eliminate sources of attraction. Produce which has ripened should be eaten, discarded or refrigerated. Cracked or damaged portions of fruits and vegetables should be cut away and discarded in the event that eggs or larvae are present in the wounded area. A single rotting potato or onion forgotten at the back of a closet, or fruit juice spillage under a refrigerator can breed thousands of fruit flies. So can a recycling bin stored in the basement which is never emptied or cleaned.

Common House Fly

House flies are not only nuisance pests while buzzing around homes, but they are potential disease carriers. House flies have short lifespans, but they can quickly reproduce in large numbers, leading to large house fly populations.

Biology: House flies are usually gray in appearance and display four black stripes on their thorax. Adult house flies are about 1/8-1/4” (4 to 7.5 mm) long. They have slightly hairy bodies, a single pair of wings and compound red eyes, which contain thousands of individual lenses that allow them to have wider vision. Female house flies are usually larger than males. House flies do not have teeth or a stinger. House fly eggs resemble small grains of rice. The eggs hatch into larvae, also known as maggots, which range in size from about ¼-3/8” (7-10 mm) long. Maggots are cream colored with a greasy appearance. When entering the pupal stage, maggots develop dark, hard outer shells, legs and wings, ultimately emerging as full-grown adult flies.



Prevention: House flies take advantage of structural issues, such as damaged weather stripping or torn screens, in order to enter a household. Make sure all windows have proper working screens and doors are not left open.

Horse Flies

Adult horse flies typically feed on nectar, but females require a blood meal before they are able to reproduce effectively. Female horse fly bites, especially in large specimens, can be quite painful because their mouthparts are used for tearing and lapping, as opposed to mosquitoes, which simply pierce the skin and suck blood. Female horse flies are also persistent and will generally continue biting a host until they either succeed in procuring their blood meal or are killed. They are even known to chase their intended targets for short periods of time. Some species are vectors of disease organisms but in the U.S. most horse fly-vectored diseases only involve livestock.

Biology: Horse flies are typically woodland or forest dwellers. Species usually feed during full daylight and are most evident on windless, hot, sunny days. In general, larvae develop in wet soil close to bodies of water. Adult horse flies are fast, strong fliers and capable of flying for more than 30 miles, though they generally do not disperse widely. They most often attack moving and dark objects. Horse flies often rest on paths and roads, especially in wooded areas, where they wait for potential hosts. Horse flies are attracted to light and will sometimes congregate at windows. They have grayish-black bodies, their eyes are often large and green or purple with horizontal strips. Their bodies are stout and do not have bristles. They are around 3/8 – 1/8″ long.

Prevention: During outside activity, wear light-colored clothing and insect repellent to prevent horse fly bites. To prevent them from entering your home or business, make sure your screens are in proper working order. 


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