Drain Flies vs. Fruit Flies: Which Tiny Winged Pest Is Invading Your Home?

If the song “Shoo Fly, Don’t Bother Me” is ringing in your ears, you may be dealing with a bothersome fly infestation in your home. There are drain flies (also known as moth, filter, or sewage flies) and fruit flies (also called pomace or vinegar flies) to contend with. But how do you know the difference between drain flies and fruit flies to figure out the best solution to get rid of them?

These tiny flying pests that often hang out in the kitchen are often mistaken for each other. Fortunately, there are a few distinct characteristics to tell them apart. By understanding their appearance, behavior, feeding and breeding grounds, and the time of day they are most likely to appear, you will be able to tell which type of fly has moved in to cause havoc inside your home. The following tips will also help prevent a drain fly or fruit fly infestation from happening again in the future.

Drain flies are darker and furrier than fruit flies.

While both types of flies have small bodies, fruit flies have a rounded, slender silhouette with clear wings, whereas drain flies have a fuzzy, moth-like appearance. “Drain flies belong to the Psychodidae family and have a more moth-like fuzzy appearance due to their hairy bodies and wings,” says Lorne Hanewich of Clark’s Termite & Pest Control, a service with several offices in central South Carolina. “The dark coloration of drain flies helps them blend into the organic matter (the ‘guck’) found in drains and sewage systems,” he adds. Drain flies are 1.5 mm to 5 mm long and have a brown, black, tan, or gray exoskeleton.

The size of a fruit fly tends to be 3 mm to 4 mm long, and fruit flies have brownish-yellow stripes or spots, often appearing brown or tan in color. Drain flies have red eyes, and while fruit flies can also have red eyes, more often they have dark-colored eyes.

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Fruit flies and drain flies prefer different feeding and breeding grounds inside a home.

The best clues to help decipher between fruit flies and drain flies is where they lay their eggs and what they eat. “Fruit flies are attracted to overripe fruits, vegetables, and fermenting liquids, making kitchens and garbage disposal areas common infestation spots,” says Hanewich. These pests can also be found in or around fruit bowls, sink drains, empty bottles, garbage bags, mops, and cleaning rags. They are attracted to the sugar found in fruits and vegetables, especially as yeast and mold start to break them down as they decay. Fruit flies are also attracted to meat, dairy, grains, garbage, and other items that provide a food source in a dark, damp spot like sewer and water lines.

“Drain flies, on the other hand, lay their eggs in the organic matter lining the walls of drains, sewage pipes, and septic tanks,” notes Hanewich. If you have ever wondered what causes drain flies, they are attracted to decomposing material inside these areas, which they feed on. And they lay their eggs in the gelatinous slime that collects along the walls of the drain. They can often be spotted flying out of an otherwise clean sink, which can be alarming. Drain flies thrive in damp areas and in standing water, such as an unused toilet. The favorite place for drain flies to feed and breed is in clogged drains, so be sure to fix backed-up drains to prevent a drain fly infestation.

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Drain flies are nocturnal, while fruit flies tend to be more active during the daytime. 

To help determine the type of fly you’re seeing, pay attention to the time of day they’re most active. Hanewich explains: “Drain flies are most active during the evening and night, making them more likely to be noticed when lights are dimmed. Fruit flies are diurnal, are attracted to light, and are commonly seen flying around kitchens and fruit bowls during daylight hours.” The way each type of fly enters the home is also illuminating. Fruit flies usually get into the house as eggs on the surface of organic matter like fruits and vegetables. Drain flies sneak into the kitchen and bathrooms through drains, windows, and the basement. They are often found resting on the walls or near breeding materials.

DIY traps can help you catch and identify which flying pest you’re dealing with.

Sometimes the only way to really figure out the type of fly invading a home is to catch a couple and examine them closely. It’s fairly easy to construct a DIY trap that will kill the bugs and help you make an ID. A common DIY trap for fruit flies, according to Hanewich, involves using apple cider vinegar as bait in a container covered with plastic wrap and punctured with small holes. Other fruit fly traps use a liquid bait or a light to attract the insects into the trap where they are then killed using electric shocks, adhesive pads, or some sort of physical construction they can’t get out of. In terms of how to kill drain flies, Hanewich says, “A DIY trap can be created using a mixture of sugar, water, and dish soap in a container, placed near affected drains.”

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Regular cleaning is the best way to get rid of (and prevent) an infestation of both types of flies.

The University of Maine Cooperative Extension recommends regular cleaning of drains or places where fermenting materials can accumulate to address fly infestations. However, there is a specific method of cleaning to get rid of the annoying pests, according to Jerry Wang, owner of DIY Pest Warehouse. “Fruit flies will lay eggs around decaying fruits and vegetables. When disposing of fruits and vegetables, the trash bags must be sealed so that air doesn’t come in and out,” Wang says. This prevents any fruit flies from escaping, he says, “and when the eggs hatch, they will be stuck inside the trash bag.”

When dealing with drain flies, Wang highlights the importance of properly cleaning kitchen sink pipes. “There is a U-shape part of the sink pipe. Sometimes there may be food sediments that build up on the bottom part of the pipe,” he says. “Because of that, food debris can get trapped there. That’s where the drain flies will lay eggs. Flush out the pipe with strong water pressure and make sure it’s 100 percent clear.” This is the best way to get rid of drain fly larvae and mature flies around the kitchen sink.

Follow these additional cleaning tips to prevent fruit flies and drain flies from becoming a problem:

• Empty and clean garbage cans and compost bins frequently.
• Dispose of overripe fruit.
• Clean and tighten food container lids.
• Wipe down counters and tables promptly after mealtimes.
• Clean sink drains with a bottle brush and a grease-cutting cleanser followed by a hot-water rinse.
• Launder dish towels and hand towels regularly.
• Dry mops thoroughly since they are a common breeding ground for fly eggs and larvae.