If the little fly is by the fruit bowl or the food caddy and has red eyes, it is a fruit fly. If a black gnat sits on the soil of your houseplant, it is a fungus gnat. It sounds like a detail, but the fix is completely different: one breeds in fermenting fruit, the other in wet potting soil.
What do fruit flies and fungus gnats look like?
| Fruit fly | Fungus gnat | |
|---|---|---|
| Colour | light brown to tan | black to dark grey |
| Eyes | bright red | dark |
| Body | stocky and rounded | slender, long legs and antennae |
| Size | 2 to 4 mm | 2 to 4 mm |
| Where you see them | fruit bowl, food caddy, bottles, drain | on and around the potting soil |
| Flight | quick short hops, lands on food | slow and fluttering, walks a lot |
Fungus gnats are the tiny black gnats that rise from houseplant soil when you water.
Where do fruit flies and fungus gnats come from?
Fruit flies follow fermentation: ripe fruit, juice and wine residue, the food caddy and the damp film in drains. The eggs often come home with fruit from the shop. Fungus gnats lay their eggs in damp, rich potting soil. They arrive with a new plant or a bag of compost and multiply wherever the soil stays wet for long.
Are fruit flies and fungus gnats harmful?
Neither of them bites or stings. Fruit flies can carry bacteria and yeasts from spoiled residue onto your food, and fruit with eggs on it goes off faster. Fungus gnats are only a nuisance as adults, but their larvae feed on fine roots in a heavy infestation. Cuttings, seedlings and young plants can struggle as a result.
How do you get rid of fruit flies?
Remove the source: throw out overripe fruit, rinse bottles, flush the drain. Then put out a trap with a lure that smells of fermentation. See the traps under get rid of fruit flies.
How do you get rid of fungus gnats?
In the pot. Let the top two to three centimetres of soil dry out between waterings, because the larvae need moisture. Put yellow sticky traps in the pots so the gnats stop laying new eggs. In a heavy infestation, tackle the larvae in the soil with nematodes. See the sticky traps and nematodes under get rid of fungus gnats.
Want to know more? Our guides explain how fast fruit flies multiply and whether fungus gnats harm your plants.
Use biocides safely. Always read the label and product information before use.
