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Harmless

Fruit flies and drain flies

Fruit fly

Drosophila melanogaster
Also called vinegar fly, common fruit fly, pomace fly, gnat (loosely)

Fruit flies do not bite; they are a kitchen nuisance that breeds in overripe produce and sticky residue, so toss food they have been crawling on.

Fruit fly, photo 1
Photo: glmory, CC0, via iNaturalist
Sizeabout 3 mm (1/8 inch) long
Where in the houseKitchen, pantry, garage, basement
WhenYear-round indoors, most common in late summer and fall when ripe produce is plentiful.

Check these features

  1. Tiny tan to yellowish-brown fly with a darker rear end
  2. Bright red eyes (easy to see with a magnifier)
  3. Clear wings held flat over the back
  4. Hovers slowly around fruit bowls, trash, recycling, wine and vinegar
  5. Whitish, legless larvae in mushy fruit or wet residue

Bites and stings

Does not bite people.

What to do

  1. Find and remove what they are breeding in: overripe fruit, a forgotten potato or onion, spilled juice, sticky recycling, a dirty mop, or the bottom of the trash can.
  2. Refrigerate ripe produce, rinse bottles and cans before recycling, and empty trash often.
  3. Tape a clear plastic bag or cup over a sink drain or disposal overnight; flies caught inside mean the drain is a source and needs scrubbing.
  4. Use fruit fly traps or a jar of cider vinegar with a drop of dish soap and a plastic-wrap cover with small holes to catch adults.
  5. Throw out food flies have been crawling on for a while and wipe counters; sprays only kill adults and do not fix the source.

Look-alikes

Drain fly (moth fly)Drain flies are gray and fuzzy with broad, hairy, moth-like wings held like a tent, hop rather than hover, and rest on bathroom walls near drains, while fruit flies are smooth, tan, red-eyed and gather near fruit, trash and drinks.
Fungus gnatFungus gnats are slender and dark with long legs and long antennae, look like tiny mosquitoes, and hang around damp houseplant soil rather than fruit.
Phorid flyPhorid flies are humpbacked and tend to run across surfaces in quick bursts instead of flying, and they often point to a hidden plumbing leak or decaying material.

Why it came inside

Adults are drawn by the smell of fermenting fruit, juice, beer, wine and vinegar and fly in through screens or ride in on produce. They breed in overripe fruit and vegetables, stored potatoes and onions, garbage disposals and drains, recycling, and damp mops and rags.

Keep it out

  • Keep ripe fruit in the refrigerator and do not leave cut fruit out.
  • Rinse recyclables and keep trash and compost containers lidded and clean.
  • Wring out and dry mops, sponges and rags.
  • Keep fine-mesh screens on windows and doors.

What helps

Links go to Amazon search results so you can compare current options. As an Amazon Associate I earn from qualifying purchases. Always follow the product label.

Fruit fly traps

Catch the adults, but the fix is finding and removing the ripe fruit or drain film where they breed.

See options on Amazon
Screen repair kit

Patches or replaces torn window and door screens, one of the most common ways insects get in.

See options on Amazon
Hand lens

A 10x magnifier makes small features easier to check, like eye patterns, markings or the shield on a tick.

See options on Amazon

Sources

  1. University of Kentucky Entomology (ENTFACT-621)
  2. University of Maryland Extension
  3. University of Wisconsin-Madison Extension
  4. University of Wisconsin-Madison Division of Extension, Marinette County
  5. Connecticut Agricultural Experiment Station (drain fly comparison)

Checked October 18, 2026. Rating backed by 3 sources. How we rate danger.

Harmless

Drain fly

Psychoda
Also called moth fly, sink fly, filter fly, sewer gnat, bathroom fly

Drain flies do not bite; they are a sign of slimy buildup in a drain or a hidden plumbing problem, and they go away once the source is cleaned.

Drain fly, photo 1
Photo: Paul Cook, CC BY 4.0, via iNaturalist
Sizeabout 2–5 mm (1/16 to 1/5 inch) long
Where in the houseBathroom, kitchen, basement, garage
WhenYear-round indoors; often noticed after a drain or guest bathroom has gone unused.

Check these features

  1. Tiny gray to black fly that looks fuzzy, like a miniature moth
  2. Broad, hairy wings held like a peaked roof or tent over the body at rest
  3. Rests on bathroom and kitchen walls near sinks, tubs and showers
  4. Weak flier that moves in short, jerky hops of a few feet
  5. Larvae are tiny gray legless worms living in the slime inside drains

Bites and stings

Does not bite people. Very large numbers have occasionally caused allergy symptoms in sensitive people.

What to do

  1. Find the source: tape a clear cup or plastic bag over each suspect drain and sink overflow overnight, and wrap clear tape around the base of the toilet; flies caught inside point to the breeding spot.
  2. Scrub the inside of the drain, trap and overflow with a stiff pipe brush to remove the slime where larvae live.
  3. Use an enzyme or biological drain cleaner afterward to keep buildup from returning; boiling water and pesticides alone do not reach larvae hidden in the slime.
  4. Run water in seldom-used sinks, tubs and floor drains regularly.
  5. If flies keep coming with clean drains, check for a broken pipe, failed toilet seal or wet crawlspace and have a plumber repair it.

Look-alikes

Fruit flyFruit flies are smooth, tan and red-eyed with clear wings and hover around fruit, trash and drinks, while drain flies are gray, fuzzy and moth-like and sit still on walls near drains.
Fungus gnatFungus gnats are slender with long legs and narrow clear wings, like tiny mosquitoes, and come from damp houseplant soil rather than drains.
Clothes mothClothes moths are golden-tan with a reddish head tuft and are found near wool in closets, not gray and fuzzy near sinks.

Why it came inside

They breed in the slimy film of bacteria and organic gunk inside sink, tub, shower and floor drains, overflow holes, and seldom-used pipes, or around a broken pipe or leaking toilet seal under a floor. Outdoors they breed in clogged gutters, septic and sewage areas, and wet compost.

Keep it out

  • Clean drains and overflow holes on a regular schedule.
  • Run water through guest-bath and basement drains at least weekly.
  • Fix leaks and moisture problems under sinks, slabs and crawlspaces.
  • Keep gutters clear and garbage cans clean and dry.

What helps

Links go to Amazon search results so you can compare current options. As an Amazon Associate I earn from qualifying purchases. Always follow the product label.

Sticky traps

Flat glue traps set along walls and in corners show what is moving through and where. Place them where pets and children can't reach.

See options on Amazon
Hand lens

A 10x magnifier makes small features easier to check, like eye patterns, markings or the shield on a tick.

See options on Amazon
Dehumidifier

Keeping a basement at about 50 percent humidity or lower makes it less welcoming to the bugs that need damp air.

See options on Amazon

Sources

  1. Connecticut Agricultural Experiment Station
  2. Washington State University Extension (PestSense)
  3. Utah State University Extension
  4. Oklahoma State University Extension
  5. University of Wisconsin-Madison Division of Extension, Marinette County

Checked October 18, 2026. Rating backed by 3 sources. How we rate danger.