How to get rid of fruit flies in the kitchen

Small flies with red eyes hovering over the fruit bowl, bin or sink
Flies around empty bottles and cans waiting for recycling
Flies that come back a few days after you thought they had gone

Why it happens

The University of Kentucky's entomology fact sheet ENTFACT-621 describes fruit flies as about 1/8 inch long, usually with red eyes, a tan front and a black rear. They are attracted to ripened or fermenting fruit and vegetables. They arrive on produce that was already infested when you brought it home, and adults can fly in through inadequately screened windows and doors.

They multiply fast. The same fact sheet says a female lays about 500 eggs and the whole life cycle from egg to adult can take about a week. University of Wisconsin guidance, Fruit Flies in the Home, gives eight to 10 days. Eggs are laid near the surface of fermenting or rotting material, and the larvae feed on the yeast that grows there.

Very little is needed. Kentucky notes that all a fruit fly needs to develop is a moist film of fermenting material: a single rotting potato or onion forgotten at the back of a cupboard, fruit juice spilt under a fridge, or a recycling bin that is never emptied or cleaned can breed thousands of flies.

The breeding sites the two universities list include:

• over-ripe or damaged fruit and vegetables, and stored onions, potatoes and squash;
• banana peels or apple cores swept under furniture or appliances;
• drains, waste disposal units and damaged drain traps holding fermenting organic matter;
• the bottom of bins where vegetable matter has caked on;
• empty bottles and cans in the recycling, especially old condiment bottles;
• mops, rags, brooms and buckets that are soiled or smell sour;
• the drip tray under a fridge.

How to fix it

1. Search for every breeding site. Wisconsin is clear that the only way to completely stop the problem is to find and eliminate the breeding sites. Kentucky warns this can take thought and persistence. Work through the list above room by room, including cupboards where vegetables are stored.
2. Deal with the produce. Kentucky advises eating or refrigerating ripened produce and cutting away damaged parts of fruit. Throw out anything rotting.
3. Empty and clean bins and recycling. Rinse bottles and cans, and clean the bottom of bins and the recycling box where residue collects.
4. Wash or replace mops, cloths and buckets that are soiled or smell sour, and let them dry.
5. Check drains you cannot see into. Kentucky's method is to tape a clear plastic food storage bag over the drain or waste disposal opening overnight. If flies are breeding inside, the adults emerge and are caught in the bag. A drain that tests positive is a breeding site to clean out; if a drain is also slow or blocked, deal with that as a separate plumbing problem.
6. Trap the adults that are left. Roll a sheet of paper into a funnel, put it in a jar and bait the jar with a few ounces of cider vinegar, as Kentucky describes; slices of banana also work as bait. Wisconsin mentions a jar baited with ripe bananas, pears or wine with a funnel on top, and notes that old wine bottles with residue inside catch adults too. Place traps wherever you see flies.
7. Use a spray only as a last step, if at all. Kentucky says a pyrethrum-based aerosol may be used on the remaining adults once the source is gone. Wisconsin adds that sprays containing pyrethrins kill only the adults present at the time of spraying and leave no residual control. Follow the product label.
8. Keep them out. Kentucky recommends tight-fitting 16 mesh screens on windows and doors, and sealed containers for home-preserved food and home-fermented drinks.

Check that it worked

After the breeding sites are gone, the number of flies in the traps should drop over the following days and then stop. If flies are still being caught after a week or so, there is a breeding site you have not found yet: go back to the list, check the bag test on every drain and look under appliances. Kentucky's point that the life cycle can be completed in about a week means a missed source shows up again quickly.

Why this is more than a nuisance

Kentucky's fact sheet notes that fruit flies can contaminate food with bacteria and other disease-producing organisms, which is a good reason to keep ripe produce in the fridge while you clear the problem.

Fruit flies are a sanitation problem rather than a pest-control problem. Traps and sprays deal with the flies you can see, but only removing what they breed in stops new ones appearing.