Fruit flies and fungus gnats are often confused. Both are small, fly around the house and are hard to catch. Yet they are two completely different insects with different lifestyles, breeding sites and control methods.
What do they look like?
Fruit flies are light brown with distinctive red eyes and grow to about 3 to 4 millimetres. Fungus gnats are slightly larger, darker and look more like a small mosquito than a fly. They move more slowly and are less agile in the air than fruit flies.
Where do they come from?
Fruit flies are attracted to fermenting or rotting fruit and vegetables. You'll find them mainly around overripe fruit, bins, empty bottles and damp drains. Fungus gnats live and breed in moist potting soil. They almost always come from houseplants, and their larvae feed on plant debris and sometimes the roots of your plants.
What damage do they cause?
Fruit flies are mainly a hygiene problem. Fungus gnats are harmless as adults, but their larvae can damage plant roots in the case of a large infestation.
How do you get rid of them?
For fruit flies: remove the source. Throw away overripe fruit, keep drains clean and use a fruit fly trap. For fungus gnats: let the top layer of soil dry out between waterings, as larvae need moisture to survive. Sticky traps near plants help catch adult gnats.
Summary
Seeing small flies around your fruit bowl or bin? You probably have fruit flies. Flying around your plants and staying close to the ground? Almost certainly fungus gnats.