Why Fruit Flies Keep Coming Back (and the Drain Step That Stops Them)

Step by step

1. 1

   Set a trap where you see them

   Pour a few ounces of apple cider vinegar (about 1/4 cup) into a small jar or bowl, and add a few drops of dish soap. Cover the top with plastic wrap and poke a few small holes in it with the tip of a pen. Set it wherever the flies gather.

   Texas A&M says traps alone rarely control flies, but they catch adults while you clean and help you pinpoint where they come from. Keep the holes small, because Cornell says a trap opening should be under a quarter inch.

   What it looks like: tiny flies floating in the vinegar. The soap breaks the surface of the liquid, so flies that land sink instead of standing on it. Cornell says to check the trap daily.

2. 2

   Put away the ripe fruit

   Eat ripe fruit, put it in the fridge, or throw it out. Cut away any cracked or bruised parts and toss them. Then look for produce stored out of sight, because the University of Kentucky says a single rotting potato or onion can raise a lot of flies.

   Overripe fruit goes in an outside trash can, not the kitchen one.

3. 3

   Wash the trash can and rinse the recycling

   Pull the bag out of the kitchen trash can and look at the bottom. Texas A&M says the wet bottom of a can, where a liner leaked, is a common breeding spot. Wash it with soap and water and let it dry before you put a new bag in.

   Rinse bottles and cans before they go in the recycling, and empty kitchen compost often.

1. 4

   Dry out the rags, sponges and mop

   Wring out dish rags and sponges, let them dry all the way, and swap them out often. Hang the mop up off the floor to dry. Cornell says fruit flies can breed in mop heads and dish rags soaked with food or drink, and a sour, damp sponge is the same kind of spot.

2. 5

   Test your drains with tape

   Put a strip of clear packing tape across each drain you suspect, without covering the whole opening. Texas A&M says to leave some air space, because flies may not come up through a fully sealed drain. Check the tape the next morning.

   What it looks like: if tiny flies are stuck to the tape, you have found a breeding drain.

3. 6

   Scrub that drain and flush it

   Put on gloves. Take out the drain stopper or strainer if it lifts out. Push a stiff, narrow brush down the drain and scrub the inside of the pipe as far as it reaches, which breaks up the film where the flies breed. Then flush the drain with hot water.

4. 7

   Follow up with an enzyme drain product for a few weeks

   If you cannot reach the film with a brush, use a drain product made to break down that buildup. Use it exactly as its label says. Texas A&M says these products usually need repeat treatments over several weeks, so one dose is not the end of it.

   If your home has a septic tank, make sure the label says the product works with septic systems.

When it will not work, and what to do instead

Sometimes the flies keep coming even after a good cleanup. Here is what that usually means.

• There is still a breeding spot somewhere. The University of Wisconsin says you often have to be a good detective. Look for food swept under appliances and check the fridge’s drain pan. Texas A&M adds loose lids on vinegar, wine, beer or cider, and recycling bins with unrinsed bottles.
• You poured bleach or boiling water down the drain. That makes sense to try, since it seems like the strongest thing in the house. But UC Integrated Pest Management says neither one removes the film inside the pipe, so it helps for a short time at best.
• They came home with the groceries. Cornell says fruit flies often arrive as eggs or larvae on store-bought produce. Store produce the right way and keep up the trap for a week.
• They are fuzzy little moth-shaped flies at the bathroom sink. Those are drain flies. Skip the fruit hunt and go straight to Steps 5 to 7.

Why it works

Fruit flies are not really after your fruit. Their young feed on the yeast that grows on food as it ferments (slowly breaks down and turns sour). Cornell says the larvae need that yeast. So anything sweet and going sour, from a soft banana to the slime in a drain, can be a nursery.

The numbers are why they seem to come out of nowhere. One female can lay about 500 eggs, and the University of Kentucky says the whole trip from egg to adult can take about a week.

That is why a trap alone never finishes the job. It is a little like mopping under a leaky faucet without turning off the water. The University of Wisconsin says the only way to stop them completely is to find and get rid of where they breed.