The common fruit fly, Drosophila melanogaster, is a familiar household pest often seen buzzing around kitchens. True fruit flies are drawn to the byproducts of decay, specifically the yeast and bacteria thriving on overripe or rotting organic matter, where they feed and lay their eggs. The insects found attacking houseplant roots or foliage are typically a different type of fly entirely, leading to frequent misidentification. Addressing an infestation requires understanding this distinction, as the correct pest requires a targeted control strategy.
What the Common Fruit Fly Actually Eats
The fruit fly’s diet is intrinsically linked to the process of fermentation, not fresh produce. Adult flies are primarily attracted to the alcohol and volatile organic compounds released by yeast and bacteria colonizing decaying fruit. They feed on these microorganisms, which provide the necessary protein and nutrients for reproduction.
The fruit serves as a moist, sugary substrate where yeast grows and where the female fly can lay up to 2,000 eggs. Once the larvae hatch, they burrow into the softened, fermenting material, feeding exclusively on the yeast and bacteria. This preference means Drosophila infestations are confined to areas with decomposing food, spilled sugary liquids, or poorly maintained drains, rather than healthy plants.
The Pests That Are Mistaken for Fruit Flies
The small flies seen flying near potted plants are most often Fungus Gnats (family Sciaridae). These insects differ from fruit flies because their life cycle centers around the soil and roots of living plants.
Fungus Gnats
Fungus Gnat larvae feed on fungi, algae, and decaying organic matter found in the top few inches of moist potting soil. If the larval population is high, they will chew on fine root hairs and tunnel into the plant’s roots. This root damage causes symptoms like sudden wilting, yellowing leaves, and stunted growth, especially in seedlings. Adult Fungus Gnats do not feed on the plants, but their presence indicates that destructive larvae are active beneath the soil surface.
Shore Flies
Another common misidentification is the Shore Fly. Shore Flies are slightly stockier and prefer very wet, algae-rich environments, often appearing near waterlogged soil. While both Fungus Gnats and Shore Flies are attracted to the damp conditions of overwatered houseplants, the Fungus Gnat is the primary culprit behind direct plant root damage. These pests require moist soil to breed, a habitat entirely different from the fermenting fruit preferred by true fruit flies.
Telling the Difference Between the Flies
Observing the insect’s location and flight pattern is the most direct way to distinguish between a fruit fly and a Fungus Gnat. Fruit flies congregate around kitchen counters, fruit bowls, garbage cans, or sink drains. Conversely, Fungus Gnats emerge from the soil of a potted plant when the pot is disturbed.
Visual inspection also reveals clear differences in appearance. Fruit flies have a rounded, stockier body, are typically tan or light brown, and possess large, bright red or dark eyes. Fungus Gnats are more slender with long, dangling legs, are uniformly dark gray or black, and have small, dark eyes. Fruit flies exhibit a slow, hovering flight, whereas Fungus Gnats are weak fliers that often run or crawl across the soil surface.