To get rid of flies in a restaurant, find the places where they breed and clean those, because fly lights only catch the adults. One female fruit fly can lay up to 500 eggs, and they become adults in 8 to 10 days in warm weather (Cornell IPM). So every fly your light catches is replaced next week. That stops only when you remove the slime in the drains, the sugar under the bar mats and the rotting food behind the equipment. Start tonight with a tape test on every drain, then scrub the ones that catch flies.
Why fly lights and mopping don't stop them
A fly light kills flies that are already grown. The eggs and the larvae, the small white worms that turn into flies, sit somewhere wet and dirty that your cleaning doesn't reach.
Mopping cleans the floor, not the inside of a drain pipe. It can even make things worse. A wet mop left in dirty water overnight is a place where fruit flies breed, and so are wet rags and dish towels (Cornell IPM).
House flies grow even faster. A female lays several batches of 100 to 150 eggs, and in summer they can go from egg to adult in 7 days (UC IPM). Kill the eggs where they grow, or you'll be killing the same number of flies every day.
Which fly you have tells you where to look
Look at the sticky board inside your fly light. The dead flies on it tell you which fly you have, and each fly breeds in a different place.
| Fly | How to spot it | Where it breeds |
|---|---|---|
| Fruit fly | Small, tan, often red eyes | Old fruit, beer, soda, wine, drains, mops, bar mats |
| Drain fly | Small, grey, fuzzy wings like a tiny moth | The slime inside drains |
| Phorid fly | Small, with a humped back, runs fast before it flies | Drains, and wet dirt under a broken pipe |
| House fly | Bigger, grey, four dark lines on its back | Trash and dumpsters, and comes in through doors |
Small flies (the first three) are almost always breeding inside your building. House flies mostly come in from outside. That split tells you whether to clean first or close the doors first.
To get rid of flies in a restaurant, test every drain first
Virginia Cooperative Extension gives a simple test (2026). At close, put a piece of clear tape over each drain, sticky side down. Leave it overnight. Flies stuck to the tape in the morning mean that drain is a breeding place.
Say your old space and the new one have 14 drains between them: sinks, hand sinks, the mop sink, floor drains, and the floor sink under the ice machine. Number each drain on a sheet of paper and write the fly count next to it in the morning.
Say 5 of the 14 catch flies. Those 5 are your first job. Test the rest again in a week, because one test can miss a drain.
Test the drains nobody uses too. The U-shaped pipe under a sink holds water that stops smells and flies coming up from the sewer. In a room that sat empty for months, that water dries up. Pour a jug of water into every unused drain once a week.
Do the same with sticky cards, the flat sticky traps you can buy at any hardware store. Put one under the soda gun holder, one under the beer drip tray, one on the walk-in floor, and one in dry storage. After 2 days, the card with the most flies is closest to where they breed.
How to clean a drain so flies stop breeding
Bleach, boiling water and dish soap don't fix it. They run past the slime in seconds. Virginia Cooperative Extension says bleach is not very effective against drain flies and can damage pipes. It also says never to pour insecticide down a drain.
The flies breed in the slime stuck to the pipe walls, above the water. You have to scrub that slime off:
- Take out the drain cover and the basket, and scrub the underside of both.
- Push a stiff drain brush into the pipe as far as it goes, and scrub the walls all around. A Carlisle floor drain brush head costs $19.49 at WebstaurantStore, and a 36-inch handle costs $17.99 (September 2026).
- Scrub the small overflow holes on the sinks too. Flies breed in there.
- After the last use of the night, fill the drain with a bacteria drain foam. It sticks to the pipe walls, where a liquid only runs past, and it eats the slime that's left.
- Leave the foam overnight with no water running.
Some owners also cover each treated drain with plastic wrap overnight, so new flies can't get out. It works, but remove the wrap before the morning prep starts.
Scrub the drains that caught flies every night for 2 weeks. Fruit flies take 8 to 10 days to grow and drain flies one to two weeks, so 14 nights covers one full round. At 5 minutes a drain, 5 drains take about 25 minutes a night. After 2 weeks, scrub all 14 once a week.
If the slime comes back within days, the pipe may be coated with grease. Our kitchen drain and grease trap maintenance schedule covers how often to have the lines jetted clean.
Pest control companies also sell drain foams with insecticide in them. Let them apply those. The label is the law for any insecticide, and the wrong product in a food area is a health code problem.
The places your nightly mop misses
After the drains, these are the places that keep a fly problem alive:
- At the bar, clean the soda gun holder, the beer drip trays and the floor sink under the ice bin every night. Lift the rubber floor mats, wash them, and let them dry standing up.
- Cover cut limes and lemons and put them in the fridge at close.
- A few drops of beer or wine in an open recycling bin feed fruit flies (Cornell IPM). Rinse the bottles or tie them in a bag each night.
- Cold slows flies down in the walk-in cooler, but it doesn't kill their eggs. Once a month, take the bottom shelves out, clean the floor under them, and throw out soft or leaking produce.
- Fruit flies breed in rotting potatoes and onions. Empty the sacks in dry storage, check the bottom layer, and throw out anything soft.
- Empty the mop bucket at close, rinse the mop, and hang it with the head up so it dries.
- Once a month, pull out the fryer, the ranges and the fridges on wheels, and clean the floor and the wall behind them. In a space you just took over, do this now, because the last owner's grease is probably still there.
- Keep dirty towels and aprons in a bin with a lid, and get them out of the building at least twice a week.
Keep house flies outside
The FDA Food Code says outside doors must be solid, tight-fitting and close by themselves. A door or window that stays open needs a screen with 16 holes per inch or an air curtain (FDA Food Code 2022, section 6-202.15).
Start with the back door. If you can see daylight under it, fit a door sweep, a rubber strip along the bottom of the door. Stop staff from propping it open during deliveries and breaks.
An air curtain is a fan above the door that blows air down across the opening, and flies don't fly through it. A 36-inch model with a switch that turns it on when the door opens costs $299.99 at WebstaurantStore (September 2026).
Many health departments only accept air curtains certified to NSF/ANSI 37, the standard for food businesses, and that model isn't. Their guides often ask for air moving at least 1,600 feet per minute, measured 3 feet above the floor, at a back door. Ask yours before you buy.
The dumpster is the house fly nursery. Keep its lids closed and put it as far from the door as you can (UC IPM). House flies can grow from egg to adult in 7 days, so ask your trash company for 2 pickups a week in summer. Hose out the dumpster area when it's emptied.
Outside fly traps with bait work well, but they smell bad and pull flies toward them. Hang them on the far side of the dumpster, never next to your back door.
Where to put fly lights so they work
The FDA Food Code says an insect light can't hang over a food prep area (section 6-202.13). A zapper must also keep the dead flies inside it. In a kitchen, use lights with a sticky board, not zappers. A zapper can throw bits of fly onto food.
The National Pest Management Association says to hang lights 2 to 5 feet above the floor, where flies fly. Put them 5 to 15 feet inside a door, somewhere they can't be seen from outside. A light people can see from the street pulls more flies in.
As a rule of thumb, change the bulbs every spring, even if they still light up. The UV light that pulls flies in gets weaker long before the bulb goes dark.
Change the sticky board every month, and read it first. Count the flies on it every Monday and write the number down. If the count drops week after week, your cleaning is working.
Pest strips work, but not in a restaurant
You'll hear that no-pest strips fix everything overnight. They do kill flies fast. They give off a vapor of dichlorvos, a strong insecticide that also harms people.
The Hot Shot No-Pest Strip label says: "Do not use in kitchens (except cupboards), restaurants or areas where food is prepared or served." Cornell's New York State IPM program adds that these strips are only for closed spaces where people stay less than 4 hours at a time. It lists headaches, nausea and shaking among the effects of breathing too much of the vapor.
Using a pesticide against its label breaks federal law. An inspector who finds a strip in your storage room has a violation to write. Hang plain sticky fly ribbons in the dish area and storage instead, away from food prep.
US health code rules for flies (2026)
The FDA Food Code says your building must be kept free of insects (section 6-501.111). You must check deliveries and the building for pests, and remove the places where they live and breed.
Each state adopts the Food Code on its own schedule, and your city or county health department checks it. The section numbers above come from the 2022 edition. The FDA published a 2026 edition on September 17, 2026, so ask your inspector which one applies to you.
Cities score flies in different ways. In New York City, flies in food or non-food areas are violation 04N, a critical violation. Its points go up with how many flies the inspector sees and where. An A grade allows 13 points at most.
Keep your pest control service reports in one folder, because inspectors often ask to see them. Leave any spraying or insecticide to a licensed pest control company, and check your state's rules on who may apply pesticides in a food business.
When the flies still won't stop
If every drain tests clean and small flies still show up, look at the floor. Phorid flies coming out of floor cracks, broken tiles or grout lines are a sign of a broken drain pipe under the concrete.
They breed in the wet dirt around the break, where no cleaning or spray can reach. A plumber has to find the break with a camera, open the floor, dig out the dirty soil and fix the pipe.
Also ask your pest control company for more than a monthly spray. Ask them to name the breeding sites in writing, treat the drains with foam, and put sticky cards out to track the numbers. If they can't show you where the flies come from, get a second company to look.
Do this week
- Tonight, put clear tape over every drain in both spaces, and write each drain's fly count on a numbered sheet.
- Buy a stiff drain brush and bacteria drain foam. Scrub and foam every drain that caught flies, every night for 2 weeks.
- Clean under the bar mats, the soda gun holder, the walk-in's bottom shelves and the onion and potato sacks.
- Fit a door sweep on the back door, keep the dumpster lids closed, and ask for 2 trash pickups a week.
- Hang the fly lights 2 to 5 feet high, out of sight of the doors, with new bulbs. Count the sticky board every Monday.