Is It a Drain Fly or a Fruit Fly?
By the Clark Pest Entomology Team
Last updated: October 28, 2026
Quick answer: Look at the fly and where it sits. Small, dark, moth-like flies with hairy wings on walls near a drain are drain flies. Gray flies about 1/4 inch long with four black stripes on the thorax are house flies. Tiny red-eyed flies over fruit are fruit flies. Match yours below, then open that guide.
Which Fly Do You Have?
Clark has guides for three flies that turn up indoors across California and Northwestern Nevada. Tap the one that sounds closest. The table below helps with the tiny look-alikes.
House Fly
Gray and about 1/4 inch long, with four dark stripes on the thorax. It breeds in garbage and manure and also feeds on human food.
Drain Fly
Tiny, dark and moth-like, with fine hairs on the wings. It rests on walls near sink and shower drains and makes short hopping flights.
Blow Fly
A shiny, metallic fly that University of Minnesota Extension puts at 1/4 to 1/2 inch long. Clark lists a bright metallic blue, green or black upper body. The female lays eggs on dead animals or animal waste, so a sudden swarm indoors can point to a dead animal in a wall or attic.
Photo credits: Blow fly by Hectonichus via Wikimedia Commons, licensed CC BY-SA 4.0.
Drain Fly, House Fly, Fruit Fly or Fungus Gnat?
Size and location answer the question fast. Check the fly against these clues before you grab a spray.
| Clue | House fly | Drain fly | Fruit fly | Fungus gnat |
|---|
| Size | About 1/4 inch | About 1/8 inch | 1/12 to 1/8 inch | Commonly 1/16 to 1/8 inch |
|---|
| What it looks like | Gray with four black stripes on the thorax | Dark, with fine hairs on the wings. Holds them roof-like over the back | Brown to yellowish with red eyes and clear wings | Dark and delicate, like a small mosquito. Long, segmented antennae |
|---|
| Where you spot it | Near trash cans, dumpsters, doors and kitchens | On walls and fixtures close to a drain | Around ripe or rotting fruit | Around the soil of houseplants |
|---|
| Where it breeds | Manure and rotting material, especially garbage and dumpsters | Slimy buildup inside sink and shower drains | Damaged or overripe fruit | Soil, potting mix and other moist organic matter |
|---|
| First fix | Close lids, fix screens and clean up the trash area | Scrub the film out of the drain | Throw out overripe fruit, including fruit on the ground | Let the soil surface dry between waterings |
|---|
Tiny Flies Around the Sink or Shower
Find the drain they came from
Adult drain flies stay close to where they grew up. The UC IPM drain fly guide says adults resting on walls near a drain are a clear sign that this drain is a breeding site. Check every drain in the room. To test a drain, rub a little Vaseline or vegetable oil inside a cup or jar. Flip it over the drain opening and leave it there for 24 hours. The flies it traps point to the source.
Scrub it out, do not just pour
The larvae live in the slimy film inside the pipe. UC IPM says to scrub that film off with a hard bristle brush and an industrial drain cleaner, and to snake a slow drain first. Follow the label. It also calls boiling water and bleach a common misconception. They do not remove the film, so the best they give is short-term control.
A swarm points past one drain
Drain flies do not bite people or animals. They can carry germs from a drain to areas where sterility is important, such as food prep spaces. Very large numbers suggest a breeding site bigger than a few indoor drains, such as material beneath a leaking drain or sewage pipe.
Flies Around the Kitchen and Trash
Where house flies come from
House flies lay eggs on manure and rotting material, especially garbage and dumpsters, according to Utah State University Extension. Adults feed on that same material and on human food. The extension notes that flies can spread disease from one food source to food prep areas.
Cut off the supply
Utah State lists the fixes. Keep exterior doors shut or add automatic door closers, especially on kitchen doors. Repair screens. Keep trash containers tidy with the lids closed and place dumpsters at least 50 feet from the building. Then find and remove the breeding material itself.
Fruit flies are a smaller problem
UC IPM describes vinegar flies, also called pomace flies, as brown to yellowish with red eyes. It says most feed only in damaged or overripe fruit. Its first step is sanitation. Remove and throw out overripe fruit, including fruit dropped on the ground. See the UC IPM fruit fly guide for the full list.
What baby flies really are
A fly grows from egg to larva to pupa to adult. Drain fly larvae reach about 1/4 inch and live in drain slime, says UC IPM. House fly larvae feed on manure and decaying material, says Utah State. Find the food source and you find the larvae.
Tiny Flies Around Houseplants
Fungus gnats live in the pot
According to UC IPM, fungus gnat larvae live in soil and potting mix and feed on fungi and organic matter. They also chew roots in large numbers. Adults do not bite or damage plants. Let the soil surface dry between waterings, fix plumbing or irrigation leaks, and use yellow sticky traps to catch adults. The UC IPM fungus gnat guide says insecticides are rarely warranted indoors.
The humpbacked look-alike
If the fly runs across the counter instead of hovering, look at its back. The University of Minnesota Extension describes humpbacked flies as about 1/8 inch long with a hump when seen from the side. They are commonly found running erratically. They turn up where decaying matter collects, such as trash containers, drains and plumbing or sewer leaks, so the hunt for the source looks like the drain fly hunt.
Clark's Expert Insight
Match the fly to the room before you buy a spray. Flies at the sink came from the drain. Flies at the trash came from the trash. Flies at the plants came from the soil. A spray reaches adults in the air, not the larvae in the pipe or the pot. Chemical control is generally unnecessary for drain flies, and control stays temporary until the breeding site is gone.
Fly Questions Homeowners Ask
How do I know if I have drain flies?
Look for small, dark, moth-like flies resting on walls or fixtures near a drain. Then run the cup test. Coat the inside of a jar with Vaseline or vegetable oil, flip it over the drain for 24 hours and check for trapped flies.
How big are drain flies?
UC IPM puts adults at about 1/8 inch long. Fine hairs cover the wings, which gives them a moth-like look. At rest they hold the wings roof-like over the back.
Are drain flies harmful?
They do not bite people or animals and do not damage structures or plants. They can carry germs from a drain to nearby surfaces, so clean the drain and keep them off food prep areas.
Is it a fruit fly or a drain fly?
Check the color and the spot. Fruit flies are brown to yellowish with red eyes and gather around overripe fruit. Drain flies are dark with hairy wings and rest near drains.
Do boiling water and bleach kill drain flies?
UC IPM says they do not remove the slimy film where larvae live and give short-term control at best. It recommends scrubbing the film out with a stiff brush and a drain cleaner, then running water to confirm it flows freely.
Why are there so many flies in my house?
A big number points to a big source. Check the trash, the dumpster area and every drain. Very large drain fly numbers suggest a breeding site bigger than a few indoor drains, such as material beneath a leaking drain or sewage pipe.
When should I call a professional?
Call when you cleaned the drains and took out the trash and the flies keep coming back. A technician can look for hidden breeding sites, such as a leaking pipe, and talk through options for your home or business.