What do fruit flies look like, and how to tell them from the other tiny flies
A fruit fly is about 2 to 4 mm long, stout, usually red-eyed, tan at the front and dark at the rear. Three other tiny house flies share that size, so the tell is the shape, the eyes, how it moves and where you keep seeing it.
By The Pest GuyLast updated
The short answer
Red eyes, a stocky body, a tan front and a dark back end, hanging about the fruit bowl.
The common fruit fly is about 2 to 4 mm long with a stout, rounded body. It usually has red eyes. The front half is tan or buff and the rear half is black, often looking striped. Texas A&M's extension service puts it plainly: the stocky body and the red eyes are what set it apart from the other small flies you get indoors.
It is also called a vinegar fly, because it is drawn to vinegar and almost any decaying fruit. So you see it where those are: the fruit bowl, the bin, the recycling, an open bottle of wine. That is half the identification done for you.
The hard part is that three other tiny flies live in the same few millimetres: fungus gnats, drain flies and phorid flies. Size will not separate them. The published figures for all four overlap, and the sources do not even agree with each other on them. What does separate them is in the table below.
Fruit flies and the three tiny flies mistaken for them
Read across a row. The last column is usually the one that settles it, because each fly breeds somewhere different.
| The fly | What it looks like | What it does | Where it breeds |
|---|---|---|---|
| Fruit fly (red-eyed) | About 2 to 4 mm. Stout, rounded body. Red eyes. Tan or buff at the front, a dark striped rear. | Hovers. Drawn to vinegar and almost any decaying fruit, so it gathers at the fruit bowl, the bin and open bottles. | Overripe fruit (bananas especially), rotting onions and potatoes, spilt wine or beer, unrinsed bottles, a wet mop or dishcloth. |
| Dark-eyed fruit fly | The same shape, a little bigger at about 3 to 4 mm, and dark grey to black to the eye. Dark eyes. | Hovers, and rests on walls. | Wet, decaying matter that may be out of sight: drains, sinks, under appliances, around bathrooms. |
| Fungus gnat | Mostly 3 to 4 mm. Slender and dark greyish brown, like a tiny mosquito, with long thin legs. | Runs over the compost or flies slowly around plants. Drawn to lights, phone and laptop screens included. | Damp potting compost. The larvae live in the soil. |
| Drain fly (moth fly) | About 2 to 5 mm. Fuzzy, grey and moth-like, with hairy wings held over the body like a roof. | Flies only a few feet at a time. Sits on the wall near the drain it came from. | The film inside sink and floor drains, or sludge where water evaporates. A trickle from a pipe joint is enough. |
| Phorid fly (scuttle fly) | Fruit-fly sized or smaller. Humpbacked and darker overall, with dark veins along the front edge of the wing. | Runs and stops, runs and stops, before it takes off. Flies poorly. | Any moist, decaying matter: bins, drains, wet potting soil, a dead animal, or a leaking sewer pipe under the floor. |
Sources: Texas A&M AgriLife Extension, "Indoor Flies and Their Control" (ENTO-050); Cornell IPM, "Non-biting Flies"; Killgerm in PPC magazine, "Know your enemy: the key to tiny fly control" (September 2025); the RHS on fungus gnats; Lewisham Council's flies information sheet. The sizes are published ranges and they disagree: Cornell gives the red-eyed fruit fly as 2 mm and the phorid as 1 mm, while Texas A&M gives both as 2 to 4 mm. Fungus gnat figures run from 1.5 mm to 10 mm depending on the source; the 3 to 4 mm here is the RHS figure for the British species.
Black fruit flies, and what they usually are
Small dark flies that look like fruit flies usually turn out to be one of four things.
A dark-eyed fruit fly. These are real fruit flies with dark eyes, and Cornell describes them as dark grey to black, a little bigger than the red-eyed kind at about 3 to 4 mm. They breed in drains and around bathrooms more often than in fruit, and in wet, decaying matter that may be out of sight. That makes them harder to trace than the ones in the banana.
An ordinary red-eyed fruit fly, seen from the back. The rear half of the body is black. On a fly a few millimetres long, sitting on a wall, that is often the part you notice.
A fungus gnat. The RHS describes them as dark greyish brown, mostly 3 to 4 mm, and they look like a tiny mosquito, all legs and narrow body. If the dark flies are round your houseplants, running over the compost, this is the first thing to rule out. The side-by-side is on fruit flies vs fungus gnats, and flies in houseplants covers the plant pot itself.
A phorid or a drain fly. Phorids are about fruit fly size but darker overall, with a humped back, and they scuttle rather than fly. Drain flies are dark grey, fuzzy and moth-shaped, and they sit on the bathroom wall. Both breed in wet, decaying matter, drains included. Lewisham Council warns that drain flies do not even need a pool: a trickle from a pipe joint when the toilet flushes can be enough.
How to get a proper look at one
I can't identify your fly for you, from a photo or a description. These are the checks that let you do it yourself.
Watch where they gather before you look at the fly. Texas A&M's advice is that identifying the fly is the first step, because each kind breeds somewhere different. A cloud over the fruit bowl, flies running over the compost in a plant pot and a fuzzy fly on the tiles by the shower are three different answers before you have looked at a single wing.
Get one still. Catch it on a strip of clear tape or under a glass, put it on white paper next to something of known size, and look with a magnifier or your phone camera zoomed right in. Check the eyes first: red or dark. Then the shape: stout, slender, fuzzy or humpbacked. With a good lens there is one more tell. A fruit fly has a feathery bristle on the tip of each antenna, which Texas A&M gives as the feature that separates it from the other small indoor flies.
Watch how it moves. Fruit flies hover. Phorids run and stop, run and stop, before they take off. Drain flies fly a few feet at a time and then sit on the wall near the drain they came from. Fungus gnats run over the compost or drift slowly round the plant.
Test the drain with tape. This one comes from Texas A&M and costs nothing. Lay a strip of clear packing tape across the plughole without covering it completely, because with no airflow the flies may not come out. Check it over the next few days. If flies are stuck to the underside, that drain is breeding them, whatever they turn out to be.
If they are fruit flies, the next question is where they are breeding, and finding the source in the house goes room by room. The eggs often come home on the fruit itself, and the larvae live inside whatever is rotting. For the reassuring part: fruit flies do not bite, and nor do fungus gnats.
Types of fruit fly you might meet in the UK
Two in the kitchen, and one in the garden that behaves differently.
Indoors it is the red-eyed fruit fly and the dark-eyed ones. "Fruit fly" covers a whole family of small flies, and Texas A&M counts more than 170 species in the US and Canada alone, so the two kinds above are a working split by eye colour and habit.
The garden one is spotted wing drosophila. The RHS says it was first reported in Britain in 2012, and the males have a distinctive spot on each wing. The difference that matters to a grower is what it eats. Unlike the native fruit flies, this one can damage ripe, unblemished strawberries, raspberries, blackberries, cherries and plums. If you grow soft fruit, that is the one to read up on.
If the table says fruit fly, this is what I'd stand by the bowl
For red-eyed or dark-eyed fruit flies, a cider vinegar trap catches the adults while you clear out what they are breeding in, and Texas A&M notes a bait trap also helps you pinpoint where they are coming from. If they turn out to be fungus gnats, drain flies or phorids, the fix is in the compost or the drain.
What I’d use
Reusable cider vinegar trap
Escape-proof fruit fly trap
A two-part cup and lid you fill with about 25 ml of cider vinegar and stand by the fruit bowl.
Eight slots in the lid feed a funnel that drops flies through one 4 mm hole into the dark middle of the cup. The brightest points a trapped fly can see are pinholes too small to get through, set away from the real exit, so the way out is the place they are least likely to look.
- Ways in
- Eight slots in the lid, into one funnel
- Way out
- One 4 mm hole, under the solid centre of the lid
- Holds
- About 25 ml of vinegar, to the moulded fill line
- Size
- 6.7 cm across, 5.4 cm tall
- Refills
- None to buy. It runs on cider vinegar from the cupboard
Watch out for
- Vinegar and washing-up liquid not included.
- Made for fruit flies. Flies from a plant pot or drain need the source found.
- Tip, rinse by hand and refill once it fills up.
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About this resource
The weight here is carried by extension and public-body sources: Texas A&M AgriLife Extension's indoor flies guide, Cornell IPM, the University of Kentucky, the RHS, and Lewisham Council, with the UK trade view from Killgerm's tiny-fly piece in PPC magazine. Where they disagree on a size, the table says so rather than picking a winner. There is more on how a fruit fly trap works on the fruit fly trap page, and the whole job start to finish is on getting rid of fruit flies.
The honest limit is identification. This page tells you what separates the candidates; it cannot tell you which fly is in your kitchen, and a photograph would not change that. If a sudden mass of bigger flies is the problem, flies in the house covers it.
Common questions
What can be mistaken for fruit flies?
Three other tiny house flies, all in the same few millimetres. Fungus gnats are slender and dark, like a tiny mosquito, and live in damp potting compost. Drain flies are fuzzy, grey and moth-like, and sit on the wall near a sink or shower. Phorid flies are humpbacked and darker, and run in short bursts before they fly. A fruit fly is stouter than all of them, usually has red eyes, and hangs about fruit and vinegar.
How do I know if I have fruit flies?
Look at where they gather and at the eyes. Red-eyed fruit flies have a tan or buff front and a dark rear, and they collect around overripe fruit, the bin, open bottles and the recycling. If they keep coming from a plant pot or a plughole instead, that points at something else. I cannot tell you which fly you have, but where you keep seeing it is the strongest clue you have.
Where do tiny black flies come from?
It depends which fly it is. Dark-eyed fruit flies, which look dark grey to black, breed in wet, decaying matter that may be out of sight, often around drains and sinks. Fungus gnats are dark greyish brown and come out of damp potting compost. Drain flies breed in the film inside drains, or in sludge where water evaporates. Phorid flies breed in almost any moist, decaying matter, including bins, drains and wet potting soil.
What type of fly has spotted wings?
In a British garden, the one people mean is spotted wing drosophila, a fruit fly first reported in Britain in 2012. The adult males have a distinctive spot on each wing. Unlike the native fruit flies, it can damage ripe, unblemished soft fruit such as strawberries, raspberries, cherries and plums, so it is a pest of the fruit patch rather than the fruit bowl.
Why do fruit flies like drains?
Because they breed in more than fruit. Texas A&M lists floor drains among fruit fly breeding sites, and the dark-eyed fruit flies breed in drains and around bathrooms more often than the red-eyed kind. Drain flies come from drains too, which is why the plughole is the place to test before you assume anything.
Is my house dirty if I have fruit flies?
What they need is small and ordinary: overripe bananas, a bag of potatoes going soft, a splash of wine, an unrinsed bottle in the recycling, a damp mop. Every kitchen has some of that some of the time. The job is to find which one they are breeding in.