A house fly infestation almost always means flies are breeding close by, in garbage, pet waste or other rotting material, and the adults are finding their way inside. Killing the flies you see won’t end it. To get rid of house flies, you have to find and remove the place they breed, which Texas A&M AgriLife Extension calls the key to controlling any fly.
They multiply fast. A female can lay up to 500 eggs, according to the University of Florida, and in warm weather a house fly can go from egg to adult in as little as 7 to 10 days, according to Purdue Extension.
Why are there suddenly so many flies in my house?
Most house flies you see indoors grew up outside and flew in, Colorado State Extension notes. A sudden jump in flies usually means there’s a new breeding spot nearby: an overflowing trash can, a split garbage bag, a dumpster or pet waste in a yard.
If the flies are big, shiny and gathered at one window or room, they may be blow flies, not house flies. Iowa State Extension says a sudden swarm of those usually means an animal, like a mouse or a bird, has died inside a wall or the attic.
Where do house flies come from?
House flies lay their eggs in warm, moist, rotting material. Purdue names manure and decaying organic matter such as garbage. In the city, that means trash rooms, garbage bags waiting at the curb, compost bins and the area around restaurant dumpsters. The maggots can crawl up to 50 feet to find a dry spot to turn into adults, according to the University of Florida, so the source isn’t always right where you see the flies.
How fast do house flies multiply?
In warm weather the whole cycle is quick, according to the University of Florida:
- Eggs hatch into maggots in 8 to 20 hours.
- Maggots finish growing in 4 to 13 days.
- Pupae become adult flies in as little as 2 to 6 days in hot weather.
That’s why a single forgotten bag of trash can turn into a fly problem within a week or two.
Can house flies make you sick?
They can carry germs. The University of Florida lists Salmonella, Shigella and Campylobacter among the pathogens house flies commonly transmit, and University of Missouri Extension notes they have been shown to carry over 100 kinds. Germs ride on their feet, legs and body hairs, or in what they spit up and leave behind, according to a CDC journal article.
How do I get rid of house flies?
- Find the source. Check trash cans and bags, compost, recycling with food residue, pet waste and anything rotting under the sink or behind the fridge.
- Take out the trash every day. NYC Health advises taking garbage and recycling out of the apartment every day and keeping it in sealed bags or containers.
- Clean up pet waste in yards and litter areas.
- Fix the screens. Tight-fitting screens keep many flies out, Colorado State says.
- Use traps for the ones already inside. Colorado State is clear that no fly trap works well alone, so traps help only after the source is gone.
Sprays are the weak link. Insecticides alone can’t rid a home of flies, Purdue says, and Texas A&M notes that fogs give only short relief and don’t solve the problem. House flies can also become resistant to insecticides, according to the University of Florida.
Here’s a simple example
Say flies keep showing up in a ground-floor apartment in Queens, a dozen at a time near the kitchen window. The kitchen is spotless. The source turns out to be the building’s trash area under that window, where bags sit for two days before pickup and one has split open. Maggots in that bag become adult flies within a week or so, and a torn screen lets them in. Swatting does nothing. Getting the bags into cans with lids, cleaning the area and fixing the screen does.
How long does a fly infestation last?
As long as the source is there. Once it’s gone and no new eggs are laid, the adults already inside die off within a few weeks.
When to call a professional
Call when you’ve cleaned up and the flies keep coming, when you can’t find the source, or when you run a business where flies gather in the kitchen, storage or waste areas. Flies usually point to something else, so we find the cause and treat it as part of Integrated Pest Management, starting with a free on-site inspection. Restaurants should also read our guide to restaurant pest control in NYC.
See our residential pest control and commercial pest control, or call (347) 988-2315.
Frequently asked questions
How long do house flies live?
Adult house flies usually live 15 to 25 days and can live up to two months, according to the University of Florida. In that time a female can lay hundreds of eggs, which is why the source matters more than the flies.
Why do flies keep coming back after I clean?
The source may be outside your home: a dumpster, a neighbor’s trash or pet waste in a yard. House flies can easily travel one to two miles, according to the University of Kentucky. Check your screens and door gaps, and look around the building, not just the kitchen.
Are the big, slow flies I see in fall and winter house flies?
Often they’re cluster flies. Purdue Extension says cluster flies are larger and more sluggish than house flies, and Colorado State notes their young live in earthworms, so they don’t breed in your trash.
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