Fruit Fly vs Drain Fly vs Gnat

What’s the Difference?

Generally, the three most likely “gnats” to infest homes and businesses are fruit flies, drain flies and fungus gnats. This information will provide a brief comparison of those three pest insects.

PestDifferentiating Facts
Fruit Fly

fruit fly small image
fruit fly
Fruit Fly

  • Tan, brownish yellow or black
  • Flying around fruit, exposed food or moist areas
  • image credit:umn.edu
Drain Fly

drain fly small pic
Drain Fly
Drain Fly

  • Gray & hairy like a moth
  • Lives inside drains or pipes of showers, sinks etc
  • image source: ncsu.edu
Fungus Gnat

fungus-gnat
Fungus Gnat
Fungus Gnat

  • Dark with long legs and long body
  • Attracted to fungus found in soil around plants
  • image source: ucanr.edu/

FRUIT FLIES

Fruit flies usually enter homes on fruit that contains their eggs or larvae. Most people see these flies hovering around stored fruit or juice. Fruit flies do not cause damage, but carry diseases that can transfer to humans.

Appearance

fruit fly drawing
Image credit:okstate.edu

Size
Fruit flies are very small, only about 1/2 to 1/4 inch long.

Color
Their color ranges from tan to brownish yellow or black. Their eyes are bright red; however, some fruit fly species do not have this characteristic.

What Do they Eat?

Fruit fly adults are often seen sitting on or flying around their preferred sources of food. Foods commonly eaten by fruit flies include:

  • decomposing fruits and vegetables
  • leftover foods
  • liquids and solids that are in a state of fermentation and decomposition

Where Do They Live?

Their preferred habitats are close to places where conditions support the development of larvae – moist, out of the way and near a food source. Examples of these habitats include neglected fruit and vegetable storage areas, drains, cracks and gaps in a floor that stays moist, unused garbage disposal, garbage containers that are not clean, recycle bins with food debris and other areas where fermenting foods and moist organic matter occurs.

Life Cycle

Fruit flies develop by complete metamorphosis and go through four stages in their life cycle (eggs, larvae, pupae and adults) that can be completed in as few as a week to twelve days. Female fruit flies can lay up to 400-500 eggs in their lifetime.

More information on fruit flies.


DRAIN FLIES

Appearance

drain fly picture
Image credit: Michigan State

Since adults appear to be very small, grayish colored, hairy winged, moth-like looking critters, drain flies are also known as moth flies.

Where Do They Live?

These small flies are sometimes pests as the result of them emerging from drains in the sink, garbage disposals, lavatories and bathtubs. Their preferred habitats are obviously those drains where they feed upon the gelatinous slime that adheres to the sides of drainpipes. Infestations of these flies can also be traced back to broken or leaking pipes.

Life Cycle

Drain flies develop by complete metamorphosis and their life cycle can be completed in about one to three weeks.

More information on drain flies.

Identifying Drain Flies vs. Fruit Flies

Several factors can help to determine whether there are drain flies or fruit flies in the house.

Differences in Appearance

Drain flies and fruit flies both grow to about one-eighth of an inch in length, though there are some visual differences. Fruit flies are yellow or tan in color, while drain flies may be black, gray, or brown. Drain flies also have fuzzier, moth-like bodies.

Differences in Habitat

While fruit flies generally stay around kitchens or other eating areas, drain flies have several options. They live and breed in standing water, which may appear in several areas around the home. Basement drains, toilet bowls, and clogged gutters are only a few of the places drain flies can thrive.

Issues with Drain Flies or Fruit Flies in Homes

Both drain flies and fruit flies are annoying and unsanitary. They spread bacteria anywhere they land, including tables and food. People who ingest these pathogens may experience stomach cramps, nausea, or diarrhea. Both pests also lay hundreds of eggs at once, so infestations grow quickly.

Controlling Fruit Flies

Fruit flies eat and lay eggs in damaged areas of fruit and rotting vegetables. Damp, slimy areas in sink drains or garbage disposals also provide enough organic matter to sustain fruit fly populations, so cleaning sinks and throwing away overripe produce may deter the pests.

Preventing Drain Flies

Unlike fruit flies, drain flies do not breed in rotting produce. They feed on and lay eggs in the organic film on top of pools of water, so drying up leaks or small pools near appliances can discourage drain flies. Run hot water in sinks to eliminate the algae and fungi that sustain these pests.


FUNGUS GNATS

These pests live around moisture and mold, feeding on organic materials. They come into homes in the soil of potted plants or through open doors and windows. The pests do not cause damage, but they can be a nuisance. Fungus gnats often fly toward light sources, and homeowners find dead insects on their windowsills.

Appearance

adult fungus gnat
Image credit: NC State

Color
Fungus gnats are small, dark-colored flies with a long abdomen and legs when compared to their overall body size and shape. Although they are just about the same size, fungus gnats look much different than fruit flies and drain flies.

What Do they Eat?

As one might expect, these flies feed upon fungus growing on and in the soil. Fungus gnats also are common outdoors where they feed on fungus in mulch, leaf mold, compost and plant root hairs.

It is important to always carefully inspect plants before bringing them inside. While the annoyance is the biggest problem to homeowners and businesses, their feeding activities rarely cause damage to the plants. However, a feeding by very large infestations of fungus gnats may cause root damage and the stunting of plant growth.

Life Cycle

These flies develop by complete metamorphosis and their life cycle can be completed in about one to two weeks. Fungus gnat females lay their eggs in or on soil and thus are often found infesting houseplants, atriums, planters and potting soil that are overwatered and creating conditions for growth of fungi.

More information on gnats.

Are They Fungus Gnats or Fruit Flies?

Determining whether the problem is fungus gnats vs. fruit flies requires some knowledge about each pest. Look for the following to determine the culprit:

  • Location – Fungus gnats typically fly around house plants or windows, but fruit flies stay near food, trash cans, and drains.
  • Shape – Fruit flies have a bulbous body, whereas fungus gnats are long and slender.
  • Color – While fruit flies are brown or orange, fungus gnats are usually black.

How to stop a fly infestation.