What Are Drain Flies?

What Are Drain Flies?

Drain flies are small flying insects that breed in the organic buildup found inside drains, pipes, septic systems, and other consistently damp areas. They are also commonly known as moth flies, sink flies, filter flies, or sewer flies because of their fuzzy appearance and their tendency to gather around sinks, floor drains, showers, and other plumbing fixtures.

Although drain flies are harmless to people and pets, they can quickly become a frustrating nuisance if left untreated. Because they breed inside drains, simply swatting the adult flies rarely solves the problem. Eliminating the breeding source is the key to controlling an infestation.

 

What Do Drain Flies Look Like?

Drain flies are easy to recognize once you know what to look for.

Adult drain flies typically have:

• A gray to dark gray body

• Hair-covered wings that give them a fuzzy, moth-like appearance

• A body length of approximately 1/8 inch

• Weak, fluttering flight

• A tendency to rest on walls near sinks, showers, and drains

Unlike fruit flies, drain flies don't hover around fruit or food. Instead, they stay close to the drains where they breed.

 

Where Do Drain Flies Come From?

Drain flies develop in the organic slime that builds up inside plumbing systems. This buildup can consist of grease, soap scum, food particles, hair, and other decaying organic matter that collects on pipe walls over time.

Common breeding locations include:

• Kitchen sink drains

• Bathroom sink drains

• Shower drains

• Bathtub drains

• Floor drains

• Utility sinks

• Garbage disposals

• Basement drains

• Septic systems

• Commercial kitchen drains

Once eggs hatch, the larvae feed on the organic material inside the drain before developing into adult flies.

 

Why Do I Suddenly Have Drain Flies?

Many homeowners don't notice drain flies until adult insects begin emerging from the drain.

A drain fly infestation often indicates that organic buildup has accumulated inside the plumbing system, providing an ideal breeding environment.

Warm temperatures and excess moisture can allow drain fly populations to grow quickly if the buildup isn't removed or treated.

 

Are Drain Flies Harmful?

Drain flies are considered nuisance pests. They do not bite people or pets, nor are they known for damaging homes.

However, large infestations can become annoying as adult flies repeatedly emerge from drains and gather around sinks, showers, and bathrooms.

Addressing the infestation early helps prevent the population from continuing to grow.

 

Drain Flies vs. Fruit Flies

Although these insects are frequently confused, they are quite different.

Drain Flies	Fruit Flies
Gray to dark gray	Tan to light brown
Fuzzy, moth-like wings	Smooth, clear wings
Weak fluttering flight	Hovering flight
Breed inside drains and pipes	Breed on fermenting fruits and organic food waste
Stay near drains	Commonly found around fruit, trash, and recycling

Correctly identifying the insect helps determine the most effective treatment.

 

How Do You Get Rid of Drain Flies?

Successfully eliminating drain flies requires treating the breeding source inside the drain—not just the adult flies you see flying around.

Helpful steps include:

• Clean drains thoroughly.

• Remove grease, soap scum, and organic buildup.

• Clean garbage disposals.

• Treat affected drains where larvae may be developing.

• Continue treatment as directed until the infestation has been eliminated.

Because larvae live inside the organic buildup coating pipe walls, simply killing the adult flies won't eliminate the infestation.

Frequently Asked Questions

Do drain flies bite?

No. Drain flies are nuisance insects and do not bite humans or pets.

Can drain flies come from clean drains?

Drain flies require organic buildup to breed. Even drains that appear clean on the surface may contain buildup deeper inside the plumbing.

Why are drain flies always near my sink?

Adult drain flies remain close to the drains where they hatch and reproduce, which is why they're commonly found resting on nearby walls and ceilings.

How long does it take to get rid of drain flies?

The time required depends on the severity of the infestation and whether the breeding source inside the drain has been properly treated. Eliminating the organic buildup where larvae develop is essential for long-term control.