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.

Pest	Differentiating Facts
fruit fly	Tan, brownish yellow or black Flying around fruit, exposed food or moist areas image credit:umn.edu
Drain Fly	Gray & hairy like a moth Lives inside drains or pipes of showers, sinks etc image source: ncsu.edu
Fungus Gnat	Dark with long legs and long body Attracted to fungus found in soil around plants image source: ucanr.edu/

FRUIT FLIES

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.

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.

FUNGUS GNATS

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.