Fruit Flies & Gnats

Three insects, three fixes

The single most useful thing on this hub is the identification, because the three tiny flies people call "fruit flies" breed in three different places and only one treatment works on each.

• Fruit flies are tan or brown with red eyes, and they hover around fruit, a recycling bin, or the bottom of a trash can. They breed in fermenting residue.
• Fungus gnats are dark, delicate and mosquito-shaped in miniature, and they come off houseplant soil. They breed in wet potting mix.
• Drain flies are small, fuzzy and moth-like, and they sit still on the wall near a sink. They breed in the organic film inside a drain.

Gnats vs fruit flies vs drain flies walks the identification properly, with the behavioral tells that are easier to use than the physical ones. Get this right first — putting a vinegar trap out for drain flies is why people conclude "traps don't work".

Why a trap alone never ends it

Every trap on this hub catches adult flies. Not one of them touches the eggs and larvae in the drain, the bin, or the plant pot. A fruit fly goes from egg to adult in about a week in a warm kitchen, so as long as the breeding site is producing, you are removing adults at roughly the rate they are made.

The pattern that works is always the same: trap the adults so the room is usable, and kill the source so the problem ends. Traps are the visible half; source treatment is the half that finishes it, and how long it takes sets out the timeline you should expect once both halves are running.

• Fruit flies: empty and wash the bin, clear the drain, and move ripening fruit to the refrigerator. What attracts fruit flies lists the sources people miss, including the one under the dishwasher.
• Fungus gnats: let the top inch of soil dry out completely between waterings, and treat with a BTI product if the bloom is bad. Fungus gnats in houseplants covers the watering change that does most of the work.
• Drain flies: scrub the drain wall with a brush — not bleach, which pours straight through the film it needs to remove. Drain flies in the sink has the method.

Which trap

For fruit flies, the sealed lure traps are genuinely better than a bowl of vinegar, and we say why on best fruit fly traps and in the head-to-head between the two best-known models, Terro vs Zevo. If you would rather make one, DIY vs store-bought fruit fly traps is an honest comparison — the homemade version costs nothing and works, with two caveats.

For gnats around plants, the answer is a light-and-fan trap or sticky stakes rather than a liquid lure, since fungus gnats are not attracted to fermentation. For a whole-room, hands-off approach there are plug-in fly traps, which use light and a sticky cartridge and run silently in the background.

Bigger house flies are a different animal again, with different traps and a different source — usually something outside. How to get rid of house flies covers those.

Speed

A fruit fly problem is one of the few pest problems that can genuinely be over in 48 hours, because the adults are short-lived and the life cycle is fast. Remove the source, put a trap beside where they were worst, and the room is usually normal within two days. If it is not, you have missed a breeding site — which is nearly always a drain, a recycling bin, or a bag of potatoes at the back of a cupboard.