Fruit Flies in the Drain or Near the Fridge: Find the Source

If the fruit is gone and the flies aren’t, check the drain, the garbage disposal and the spot under the fridge. The University of Kentucky lists drains and disposals as breeding sites and even mentions spilled juice under the refrigerator. To test a drain, tape a clear plastic bag over it overnight: flies in the bag in the morning means it’s a source. Then remove the slime inside with a brush or an enzyme drain cleaner.

Flies still around after cleaning? The two traps I’d pick (why these two): TERRO Fruit Fly Trap 4-Pack Zevo plug-in trap (Amazon; as an Amazon Associate I earn from qualifying purchases)

Why Drains Breed Fruit Flies

Fruit flies don’t need a whole banana. They lay their eggs on the surface of fermenting, moist organic material, and the film inside a kitchen drain or garbage disposal is exactly that. The University of Kentucky’s fact sheet names “drains, garbage disposals, empty bottles and cans, trash containers, mops and cleaning rags” as places they breed. Washington State University adds that the larvae only need “a moist bit of fermenting material.”

The Overnight Bag Test

Evening: tape a clear plastic food storage bag over the drain or the disposal opening. Seal the edges.
Overnight: adults that hatch inside the drain fly up into the bag.
Morning: flies in the bag? That drain is a breeding site. No flies? Look elsewhere.

This is the University of Kentucky’s method. Penn State suggests the same idea for drain flies: a jar over the outlet, or a plastic bag taped over the overflow opening. Test each sink and floor drain, including the bathroom.

How to Clean a Drain That Breeds Flies

The flies breed in the buildup, so the buildup has to go. Penn State’s advice for drain-breeding flies:

Scrub it. Clean sinks, drain pipes and traps with a stiff brush to loosen the slime.
Break down the film. Bacterial or enzyme products can digest the slime layer. Washington State University mentions non-toxic biological drain cleaners for the same job.
Keep it clean. Washington State says to keep drains in tubs, sinks and showers clear of sludge, and to keep garbage pails dry and clean.

Then repeat the bag test a few days later. If flies still appear, the source may be deeper in the pipe, and a plumber or pest professional can help (Washington State also suggests a licensed professional if you can’t manage it).

Fruit Flies Around the Fridge

A fridge itself isn’t a breeding place for fruit flies, but the area around it can be. The University of Kentucky mentions spilled fruit juice under the refrigerator as a spot that can produce a lot of flies. Check:

under and behind the fridge for old spills and sticky patches,
the drip pan under the fridge, if yours has one (my tip: it collects water and sometimes spilled juice),
the crisper drawers, for a forgotten onion, a split tomato or a bag of fruit that’s turning (my tip),
the door seals, where juice can dry in the folds (my tip).

The fridge is also part of the solution: the University of Kentucky’s first sanitation step is to eat, discard or refrigerate ripe produce. Which fruit goes in the fridge and which doesn’t is in how to store fruit to keep fruit flies away.

Fruit Flies or Drain Flies?

If the flies in your sink are fuzzy and gray and rest on the wall like tiny moths, you have drain flies, not fruit flies. Penn State describes them as about one-tenth of an inch long with a fuzzy, moth-like look. The fix is the same (clean the slime), but it helps to know what you’re dealing with: fruit flies vs gnats vs drain flies.

Drain Cleaning Safety

Don’t mix drain products. The New Jersey Department of Health says to “never mix cleaning products, especially anything containing bleach”: bleach mixed with drain openers or acids can release toxic gases, and different brands of drain cleaners “can react dangerously when combined.” Use one product at a time and follow the label.
Insecticides aren’t the answer here. Washington State University lists none as recommended for fruit flies or drain flies. Never spray into a kitchen sink where you rinse food and dishes.
Switch the garbage disposal off before you clean it. InSinkErator, the disposal maker, says to make certain the switch is off and: “Do not place your hand in the garbage disposal at any time.” Use a long brush, and tongs or pliers for anything stuck in it.
Wear gloves when you scrub a drain or clean up old spills (my advice).

Questions About Drains

How do I know if fruit flies are coming from my drain?

Tape a clear plastic bag over the drain overnight. If there are flies in the bag the next morning, the drain is a breeding site. This test comes from the University of Kentucky.

How do you get rid of fruit flies in the drain?

Remove the slime they breed in: scrub the drain and trap with a stiff brush, or use a bacterial or enzyme drain product, as Penn State recommends. Then test again with a bag a few days later.

Does boiling water kill fruit flies in the drain?

The extension sources I used don’t recommend it. They focus on removing the slime with a brush or an enzyme product, because the flies breed in that buildup. My advice: skip it, because boiling water can scald you and isn’t good for every type of pipe.

Why are there fruit flies near my fridge?

Look for spilled juice under or behind the fridge, a drip pan, or produce going bad in the crisper. The University of Kentucky mentions spilled juice under the refrigerator as a breeding spot.