Flies in the House: Causes, Drain Flies and What Works

Flies in the house are dealt with by finding and removing the place where they lay eggs first; screens and traps then catch the adults that are left. House flies breed in rubbish, leftover food and rotting organic matter. Drain flies, the small fuzzy-winged flies on bathroom walls, breed in the slime inside waste pipes. According to the Texas A&M AgriLife Extension Service, that slime has to be scrubbed out, because boiling water or bleach alone is usually not enough.

Why do flies keep coming back however many I kill?

The adults are only the part you see. In hot weather a house fly can go from egg to adult in roughly a week to ten days. For as long as wet rubbish, leftovers or organic residue remain indoors or close to the house, each batch you swat or spray is replaced by the next.

Flies are more than a nuisance. Health bodies, the World Health Organization (WHO) among them, list the house fly as an insect that can carry intestinal pathogens on its legs and body and leave them on the food and dishes it lands on. Every method of fly control therefore centres on keeping clean the place where food is prepared.

Which fly is it? House flies, fruit flies, drain flies and blowflies

Naming the fly points you to its source, which is more use than spraying everywhere.

Fly	How to recognise it and where it breeds
House fly	Medium-sized and grey; circles the kitchen and the dining table. Breeds in bins, leftover food, organic waste and pet droppings out in the yard.
Fruit fly	Very small, with red eyes; hovers over fruit. Breeds in overripe fruit, fruit peel in the bin, bottles of vinegar, beer or wine left open, and damp cloths.
Drain fly	Small, with a hairy body and wings, like a miniature moth; rests on bathroom walls. Breeds in the slime inside floor drains, the trap under a sink or basin, and toilets that are seldom used.
Blowfly (large, metallic green)	Big and noisy in flight. It usually announces a dead animal, meat or fish that has gone off, or meat waste left too long.

How do I deal with rubbish and the kitchen so flies have nowhere to breed?

Use a bin with a tight lid, line it with a bag and empty it every day. Tie meat and fish scraps and prawn shells in a bag of their own.
Wash the bin and dry it at regular intervals. The residue at the bottom is a place flies particularly like to lay eggs.
Leave no dirty dishes or pans of leftovers overnight. Dry the sink, wring cloths out hard and hang them up to dry.
Put ripe fruit in the fridge, and close sugar, honey, dipping sauces and opened bottles of beer or wine.
Wipe the worktop, the hob and the floor under the kitchen units until no crumbs or grease are left.
Pick up pet droppings from the yard or balcony every day, and remove a dead rat or dead insects as soon as you find them.

How do I get rid of drain flies for good?

Scrub the pipe. Material from the Texas A&M AgriLife Extension Service in the United States explains that drain fly larvae live in the film of organic slime that coats the inside of waste pipes, traps and toilets, and that boiling water, bleach or a household drain opener usually fails to remove it. Work in this order:

Find the drain. Stick a strip of tape across the opening of a floor drain without sealing it completely, and leave it overnight. A drain whose tape has flies stuck to it is a source.
Lift the drain cover and take out all the hair and debris.
Scrub the wall of the pipe, the trap and the section just below the cover with a long-handled brush. The mechanical scrubbing is the step that counts.
Then flush with plenty of hot water to carry away what is left.
Pour water from time to time into floor drains and sinks that are rarely used, so that the water seal does not dry out and less slime dries onto the pipe.
If flies still appear after a proper scrub, the source may be a cracked pipe, a drain pit, the septic tank or water leaking under the floor. Have a plumber check.

How do I stop flies getting in?

Fit insect screens to windows, the kitchen door and the balcony door, and patch any holes you find.
Keep the kitchen door and the back door shut when they are not in use, above all near the place where rubbish is put out.
Stand a fan at the doorway or near the dining table. Moving air makes it hard for flies to fly and to settle.
Cover food that has been set out with a mesh food cover or cling film, even for a few minutes.
In a townhouse, keep the shared rubbish point and the bin outside the front door clean and lidded.

What works against flies, and what does not?

Traps and swatters catch adult flies and leave the breeding place as it was, so they always go together with cleaning. The first two rows are the ones that end the problem.

Measure	What to expect
Removing wet rubbish, overripe fruit and leftovers	Takes away what house flies and fruit flies lay their eggs in. Nothing else lasts without it.
Brushing out the drain	The effective treatment for drain flies, according to the Texas A&M AgriLife Extension Service, followed by a hot-water flush.
Boiling water, bleach or drain opener on their own	Usually not enough for drain flies, because the slime stays on the pipe.
Sticky fly paper and glue traps	Suited to monitoring and to reducing flies in a small area, and they release no chemical into the air. Hang them away from food and from people's heads, out of reach of small children and pets, and replace them when the surface is full.
Vinegar trap for fruit flies	A small cup of apple cider vinegar with a few drops of washing-up liquid, covered with cling film pierced with holes, can help catch fruit flies in the kitchen.
Electric fly-killer lamp	Better suited to a restaurant kitchen or a large space. Keep it away from where food is prepared, because killed insects can be thrown out around it, and clean the catch tray often.
Electric racket or fly swatter	Quick for a few stray flies. Wipe the surface afterwards so that no bacteria are left behind.
Aerosol fly spray	A temporary measure. While the breeding place remains, flies are back within a few days.

Is fly spray safe to use indoors?

Used as the label says, and understood as a stopgap. If you do spray:

Buy only a spray that carries a registration number issued by Vietnam's Ministry of Health, and read the label through first.
Put away or cover food, dishes, cooking utensils, children's toys and the aquarium first.
Do not spray worktops, the hob or people.
Leave the room and keep it closed for the time stated on the label, then open it up to ventilate before going back in.
Never mix two products or decant one into a drinks bottle, and keep it where children cannot get at it.

What if the flies are coming from outside my home?

If there are still many flies although the kitchen is kept clean and the drains have been scrubbed, the breeding place may be somewhere a household cannot easily inspect: a drain pit, the septic tank, a shared pipe, a void under the floor or the building's rubbish area. A survey then establishes the source before anyone decides whether a chemical treatment is needed at all.

Two signs point beyond the kitchen. Drain flies that return after the drains have been brushed clean suggest a source further along the pipework or under the floor, which is for a plumber to check. Large metallic-green flies usually signal a dead animal or spoiled meat or fish; our guide to rats and mice explains how to find and remove a carcass.

What UpClean does about flies, and how to book a survey

UpClean's survey is free and is there to locate the breeding place. The written plan and all-inclusive quote that follow say whether any product is needed. If it is, UpClean's own pest-control technicians apply it, using products registered with Vietnam's Ministry of Health. Up specialists, the identity-verified and trained staff who work in clients' homes, cover the kitchen, food and belongings beforehand, watch every point where work is done and clean the area once it is finished.

The Up Report, UpClean's record of the visit sent by WhatsApp or Zalo, notes the drains and rubbish areas that need watching. UpClean has declared its eligibility to provide pest-control services as required by regulation; the declaration and product information are available on request.

For restaurants, hotels and cafés the two halves can be arranged together: UpClean's restaurant and hotel cleaning deep-cleans the kitchen, the drain channels, the space under equipment and the rubbish store, which are the places flies breed, and pest control can be set up as a scheduled programme.

To book, send a few photos of the flies and of the places you see them to 0968 726 135 on WhatsApp or Zalo, or call between 7:00 AM and 8:00 PM on any day of the week. You can deal with UpClean in English for the enquiry, the quote and the Up Report. The specialist's name and photo reach you before the visit, so that you can register the visit with building management if your building requires it.

Pest control: The service page, including scheduled programmes for businesses.
Rats and mice in Saigon houses: Includes how to trace and clear a dead-rat smell.
Cockroaches, ants and geckos in Saigon apartments: The other kitchen and drain pests.
Book a survey: Send the request online.
Contact UpClean: All the ways to reach the office.

Frequently asked questions

Where do drain flies come from?+

From the organic slime that lines floor drains, sink traps and seldom-used toilets, which is where they breed. Tape placed across a drain opening overnight shows which pipe is the source.

Does boiling water or bleach kill drain flies?+

Usually not well enough. The Texas A&M AgriLife Extension Service's advice is to brush the slime off the inside of the pipe and only then flush with hot water.

What is the quickest way to get rid of flies in the house?+

To cut numbers fast, take the rubbish out, cover food, close the doors, and use a fan and sticky fly paper. To end it, remove what they lay eggs in: wet rubbish, overripe fruit and the residue in the drains.

Is sticky fly paper safe at home?+

It puts no chemical into the air, which suits a household. Hang it away from food and out of reach of small children and pets, and change it when it is full.

Why are there fruit flies in a clean kitchen?+

They can breed in fruit peel in the bin, the vegetable tray, an open bottle of vinegar, beer or wine, a damp cloth and even the sink trap. Check those places; a small vinegar trap helps show where they are coming from.

There are a lot of flies after the rainy season. Do I need the house sprayed?+

Not always. First clear standing water and wet rubbish and scrub the drains. If flies are still numerous after that, have the source identified by a survey before deciding on any chemical treatment.

How should a restaurant or café keep flies under control?+

Flies in a food business usually start in the rubbish store, the kitchen drain channels and pits, the grease trap, under equipment and in the ingredient store. Clean these to a fixed schedule after every shift, fit screens and self-closing doors, keep insect-killer lamps away from food preparation, and maintain a scheduled pest-control programme with an eligible provider.

Flies in the house: where house flies and drain flies breed, and how to get rid of them