1. Are you sure they're fruit flies?
Catch one of the bugs and examine it closely. If this proves to be a challenge, hang some fly paper for an hour or so to capture a few of the little buggers. Common household fruit flies (aka Drosophila) grow to a maximum size of 1/8th inch (3mm) long and typically have brownish or yellowish bodies and red eyes. They are also known to be clumsy fliers - a common experience in infested areas is to feel these little bugs kamikaze into your bare skin and face out of nowhere.
2. Get rid of the sources of the fruit fly infestation
Ok, so you're sure you've got fruit flies, now what? Now it's time to cut off their supplies - food, shelter and breeding ability.
Destroy food sources and breeding grounds
One good thing about these insects is that their food and their breeding grounds are one in the same. They 'inject' their eggs into their food, and they tend to gather in the areas of your home where they're finding food - so it's pretty easy to cut off their supply lines. You must however, go through your entire house in these steps, even if they do not occur in every room. Once you remove one source of food, they will search for more - and if they find it somewhere else then you will be starting over again from square one. Fruit flies eat and breed in moist, organic materials. This means fruits and vegetables (especially when over ripe or rotting), dirty sponges and wash-cloths, juices, spills and messes. If your infestation is typical, they are centering around your kitchen, so that's where we'll start.
Kitchens:
•Remove standing liquids and any soft materials or fabrics that are wet.
•Flush your drains and garbage disposals with ammonia or drain cleaners. Do this once every few hours for a while or partially plug the drain and fill the sink so the cleaners trickle down slowly and stay present in the pipes.
•Empty your trash before it overflows and invest in trash containers with tight-fitting lids, make sure they close securely.
•Check your dishwasher for grime collecting in the bottom and the filter. Refrain from storing dirty dishes in there until you've eliminated the incursion.
•Scour your cabinets and pantries for exposed and forgotten foods - sacks of potatoes are common culprits, so are bags of grains and legumes that have become moist (These will breed moths as well). Store fresh fruits and vegetables in the fridge until the fruit flies are eradicated.
•Check under your refrigerator and other movable appliances and furniture for hidden spills and messes.
•If you have an electric stove, lift up the burners as well as the entire top surface and check for spills inside.
•Dry the surfaces in the sink when you are not using it.
•Relocate any potted plants or herbs outside (if the weather allows) and / or apply an insecticide that is safe to use on houseplants and edibles.
•Clean underneath your sink, look for leaks and soft, moist or rotting wood
•Dispose of or clean old towels and sponges.
•Use your nose! Sniff around for anything rotten or out of place.
•Check the cracks between your kitchen appliances and the cabinets for anything that may have fallen between them.
Living areas:
•Check behind furniture for spills and messes.
•Walk around barefoot and thoroughly inspect the entire carpet for spills and moisture.
•Clean up any leftover food, plates, or drink ware.
Bathrooms:
•Flush your sink and bathtub drains with ammonia or drain cleaner(just in case).
•Inspect the cabinets underneath the sink for leaks.
Other fruit fly attractants
Fruit flies are attracted to light as well as foods - so a portable bug light can really help cut down on the population while you are working to eliminate their breeding grounds.
Eliminate all methods of entry
In some areas it's not uncommon for fruit flies to come in from the outside - especially if you have lots of bushes and vegetation nearby, or if you have trash cans or dumpster's near your entrances. If you can, remove or relocate these things farther away from your home. Ensure screens are on all of your windows, that they are undamaged, and then concentrate on sealing up any cracks or crannies around windows and doors to make sure bugs stay out. If you believe they are coming in from the outside, a small bug light may come in handy for keeping any that do make it in from fathering a new fruit fly civilization inside of your home.
3. Eradicate the resident fruit fly population
By now you should have found their hiding places and eliminated them. You will likely see the fruits of your labor very shortly - the life span of a fruit fly is less than two weeks so mark it on your calendar, and if they remain, then there is either something you missed or they are sneaking in from outside. Let's speed this process along with some fruit fly traps to kill and remove the fruit fly population, shall we?
Fruit Fly Traps
DIY fruit fly pop bottle trap Find a narrow-necked 2 or 3 liter soda bottle and fill the bottom inch or so with fruit juice, beer, soda, V8, apple cider, or vinegar along with a few drops of cooking oil or dish soap to break the liquid's surface tension so any bugs that attempt to land will get caught in the liquid. Place the bottle in the area of infestation and watch all of the little fruit flies get trapped in the bottle or trapped in the liquid inside. DIY fruit fly Bowl trap Don't have any bottles? That's ok, make this trap instead. Take any size bowl and cover the bottom with fruit juice, beer, soda, V8, apple cider, or vinegar along with a few drops of cooking oil or dish soap and then cover the top with plastic wrap. Poke several small holes in the wrap with a fork or thin knife and set it out in the area of infestation. The fruit flies will smell their way into the bowl and will be unable to escape. Store-bought fruit fly traps You can find ready-to-go fruit fly traps in hardware stores (call first) or online. They work, but so do the free DIY versions above. Bug zapper Fruit flies like light about as much as moths and houseflies so a portable, inexpensive bug zapper may be the way to go. Try to turn off all of the other lights in the area to eliminate competition from other light sources. Kill fruit flies instantly with this methods. Fly paper Fly paper is one of the oldest and ugliest insect traps around. It works poorly for catching fruit flies, too. Stick with the other methods unless you just happen to have some laying around. When deploying fly paper for fruit flies, hanging it near a bright light will increase its effectiveness.