Phorid Flies: How to Identify Them, Find the Source and Get Rid of Them

What are phorid flies?

Phorid flies are small flies in the family Phoridae, about 1/8 inch (3 mm) long, with a humped back and a habit of running instead of flying. People also call them scuttle flies, humpbacked flies and coffin flies. Across the whole family, adults range from 1/64 to 1/4 inch (0.5 to 6 mm), so some are barely visible.

Each nickname describes something real, as Mississippi State Extension explains. “Scuttle fly” comes from the quick, jerky way they run. “Humpbacked fly” describes the arched back you see from the side. “Coffin fly” comes from one of the stranger places they breed, which we cover further down. Virginia Tech and some pest companies also use “sewer fly”, a name that drain flies share.

There are about 4,000 species worldwide. In homes, two cause most of the trouble: Megaselia scalaris and Dohrniphora cornuta, according to NC State Extension. People often call them gnats or fruit flies, but they belong to a different family from both. That matters, because each of those flies breeds somewhere else and needs a different fix.

Phorid flies vs fruit flies, drain flies and fungus gnats

The quickest test is how they move. Phorid flies run across a counter in short, jerky bursts, fruit flies hover around food, and drain flies sit still. Next, check the eyes: a fruit fly’s are red, and a phorid fly’s are dark. All four are under 1/4 inch (6 mm), so size alone will not settle it.

Phorid fly features from NC State, Virginia Tech and Mississippi State. Fruit fly and fungus gnat features from NC State. Drain fly details from our own guide.

Phorid flies and drain flies can breed in the same drain, so it is common to have both in one bathroom. If the flies on your wall are fuzzy and moth-like, read our guide to drain flies in the sink and shower. If they hover around houseplants, see fungus gnats in potting soil instead.

NC State adds one more look-alike: black flies. These have longer antennae, they do not run around, and unlike phorid flies they do bite people and animals. A small fly that bites you is not a phorid fly.

Are phorid flies harmful?

Phorid flies do not bite people or pets, according to 3 extension services: NC State, Virginia Tech and Michigan State. Like all flies, they have no stinger. The real concern is hygiene: the larvae grow in rotting matter, sometimes sewage, so adults can carry bacteria onto food. NC State says this matters mostly in food businesses and hospitals.

NC State calls these cases fairly rare, so the practical risk at home is small. Still, it is worth a few habits. Cover food, keep fruit in the fridge while you have flies, and wipe counters before you cook. Throw out anything you see flies crawling on.

Do phorid flies bite at night?

No. Some forum posts insist they do, but every extension source that covers it says they do not bite. If you wake up with bites, something else is biting you, and a bite alone cannot tell you what. Our bug bite identification chart lists the usual indoor biters and the signs that should send you to a doctor.

Can phorid flies lay eggs in people?

In rare cases, yes. NC State reports a few cases of larvae in wounds, eyes or the gut, and calls them fairly rare. LA County Public Health says the cases it describes involved the open wounds of patients in nursing homes and hospitals. So the people most at risk are those who cannot keep a wound clean.

Why do I have phorid flies?

You have phorid flies because something in or under your home is wet and rotting. The larvae need moist, decaying matter from plants or animals, and Mississippi State says a little is all it takes. Indoors, if you are finding the adults, they are almost surely breeding inside, often in one of the 11 places below.

• Drain slime in sinks, tubs, showers and floor drains, and in the garbage disposal.
• Trash and recycling bins, especially the gunk at the bottom, plus compost bins.
• A lost potato or onion, or food that rolled under the stove or fridge.
• Drip pans under the fridge, the air conditioner and the dehumidifier.
• Slow leaks under sinks and around the dishwasher, washing machine and toilet.
• Mop heads, damp rags and sponges.
• Pet waste, litter boxes and damp bedding in small animal cages.
• A dead mouse, rat or bird in a wall, ceiling or crawl space.
• Dead houseplants and vases of cut flowers left too long.
• Cracked tile or missing grout where food and water collect.
• A broken drain or sewer line under the floor.

This list comes from NC State, Virginia Tech, Michigan State, Mississippi State and LSU AgCenter. As you can see, phorid flies are far less picky than fruit flies or drain flies. That is why they are so hard to pin down, and why the house can be spotless and still have them.

What attracts phorid flies?

Females seek out moist, rotting matter to lay their eggs on. Adults also fly to light, which NC State and Penn State both note. That is why you find them at windows, around lamps and near the TV, which are rarely where they breed. Also, a fly on the window tells you very little about the source.

They can come from outside, too. Michigan State says flies from outdoor trash cans, compost, lawn clippings or a septic leak can get in through screens and doorways. NC State adds that the source may not even be on your property. In an apartment, it can be in another unit or a shared drain line.

How to find where phorid flies are coming from

To find the source, map the flies, then test each likely spot. Lay sticky traps around the house, search the kitchen first, and cover every drain overnight with tape or a clear cup. If nothing turns up and the flies are worst on the lowest floor, call a plumber. The table below covers 8 places you see them.

Our table, built from the breeding sites listed by NC State, Michigan State, Virginia Tech, Mississippi State and LA County Public Health. The order is ours, from the most common source to the least.

One clue is worth knowing. NC State says pupae may coat the surfaces near where the larvae grew. So if you find tiny oval, flattened cases along a baseboard, under a sink or on the side of a bin, the breeding site is close.

Signs of a broken pipe under the floor

A broken drain or sewer line under a concrete floor is the hardest phorid fly problem to fix. Fortunately, Mississippi State says it is much less common than a simple source like rotting food. Suspect it when most of these signs line up:

• The flies are worst on the ground floor or in the basement. Maryland Extension says extremely large numbers on the first floor may mean a broken drain or sewer line.
• They come up near baseboards, floor cracks or joints in the concrete.
• Every drain tests clean, and the kitchen has no source.
• They have lasted for months, through cleaning and spraying.

The fix is a plumbing job. NC State says the concrete has to be opened, the pipe repaired and all the infested soil removed. Pest control consultants Pinto & Associates add that the soil should be replaced with clean soil, that hundreds of flies a day can come up through one crack, and that injecting insecticide into the soil rarely works.

How to get rid of phorid flies

To get rid of phorid flies, remove or clean the wet, rotting material they breed in, then dry the area and fix any leak. Trap the adults while you work. Mississippi State says insecticides are of little or no use in most cases. Expect a few more flies for 1 to 2 weeks after.

The steps below start with what costs nothing. If you have already done the search above, most of the work is behind you. Still, phorid flies are hard to get rid of when they have more than one source, so keep the sticky traps out until they stay empty.

1. Remove the source (free)

Removing the source is the whole fix in most homes. Throw out rotting produce, scrub out trash cans and recycling bins, and empty and wash drip pans. Replace old sponges and mop heads, clean up pet waste and remove dead plants. If the source is a dead animal in a wall, it has to come out, and the spot under it needs cleaning.

2. Clean drains with a brush and a microbial cleaner

For a drain that tested positive, scrub the inside of the pipe with a long, stiff drain brush, the same way our drain fly guide describes. Then use a microbial drain cleaner, the kind made with live bacteria. NC State says these products dissolve the organic buildup the larvae live in, and that foam products are preferred. Michigan State also recommends them. Follow the label for how often to repeat it.

Do the garbage disposal too. Scrub under the rubber splash guard, where scraps collect, and run the cleaner through it. LA County Public Health says cleaners like these work when they are used regularly, not just once.

3. Fix the moisture

Larvae need the material to stay damp, so drying it out stops them. Repair leaks under sinks and around appliances, and reseal a toilet that rocks or leaks at the base. Then fill floor cracks, which LA County says trap moist debris, and regrout cracked tile, which Mississippi State lists as a breeding site. Run a fan or a dehumidifier in a damp basement.

4. Trap and remove the adults

Sticky traps catch adults and show you whether numbers are falling. Virginia Tech says sticky fly tape, glue traps or light traps may reduce the adults, and that a fly swatter works too. A vacuum is quick for flies on a window. However, traps only catch the adults, so they cannot end the problem on their own.

5. Insecticides, last and only if needed

If removing the source and drying the area work, you do not need an insecticide. NC State says residual sprays can kill the adults but will not end an infestation. Virginia Tech allows an aerosol for adults in the room, but warns never to get it on food or eating utensils. Skip foggers, because the larvae stay safe inside the breeding material.

What does not work against phorid flies

Bleach, sprays and fruit fly traps are 3 common fixes that do not work on their own. NC State says bleach and standard cleaners will not kill the larvae, and warns against pouring bleach down drains. Sprays kill only the adults you see. And we found no extension testing of vinegar traps on phorid flies.

• Myth 1

  Myth: “Bleach down the drain will kill them.”

  Truth: NC State says bleach and standard cleaners will not kill the larvae or control the flies. It also warns that bleach can react dangerously with other chemicals in drain lines. Michigan State agrees. Use a brush and a microbial cleaner instead.

• Myth 2

  Myth: “A fruit fly trap will catch them all.”

  Truth: Fruit fly traps use vinegar or fruit as bait, and we found no extension testing of them on phorid flies. Readers report mixed results. A sticky trap near each suspect spot does more, because it also shows you where the flies come from.

• Myth 3

  Myth: “Boiling water will flush them out.”

  Truth: No extension source lists boiling water as a fix. Many people in the forum threads say they poured it down for weeks with no change. Scrubbing the pipe wall and a microbial cleaner are what the extension sources recommend.

• Myth 4

  Myth: “A bug bomb will clear the house.”

  Truth: LA County Public Health says space sprays, the kind a fogger releases, kill adults but do not end the infestation. The larvae stay inside the breeding material and keep producing new flies.

• Myth 5

  Myth: “Some smell will keep them away.”

  Truth: We found no testing of any scent, oil or plant as a phorid fly repellent. It is a common question, but the honest answer is that none has been shown to work.

• Myth 6

  Myth: “Phorid flies bite.”

  Truth: They do not, according to NC State, Virginia Tech and Michigan State. If something small is biting you, it is a different insect.

• Myth 7

  Myth: “If they keep coming, you need a stronger pesticide.”

  Truth: Flies that keep coming usually mean a source you have not found yet. Under a slab, Pinto & Associates say injecting insecticide into the soil rarely works. Find the source instead.

Phorid fly life cycle and how long they live

A phorid fly goes from egg to adult in about 10 days in a warm house, according to NC State and LSU AgCenter. In cooler conditions it can take up to 37 days, says LA County Public Health. A female lays 500 to over 700 eggs, which is why a few flies turn into hundreds.

Egg, larva and pupa sizes and the short larval time are from NC State. The 8 to 16 day larval range and the egg hatch are from LA County Public Health. LSU AgCenter says development is fastest at about 72 to 75°F (22 to 24°C), and slower in cooler rooms and in heat above about 82°F (28°C).

Females lay their eggs right on moist food or rotting matter. LA County says a female can lay about 40 eggs in 12 hours and about 500 in her life, while NC State puts the lifetime total at over 700. The larvae feed inside that material, then crawl to a slightly drier spot nearby to become pupae. That is why you rarely see the larvae, but you may find the empty pupal cases.

How long do phorid flies live?

Sources disagree on this number more than any other. Insects Limited and PestWest say adults live only a few days, and Insects Limited adds that they can last up to 9 days when the humidity is above 70%. Michigan State, on the other hand, says adults can survive one to two months. Either way, the adults you see are not the real problem. The larvae in the source are.

Why phorid flies keep appearing after you fix the source

Cleaning the source stops new eggs, but flies already in the pupa stage will still come out. NC State puts that stage at about 7 days. So expect new adults for 1 to 2 weeks after a real fix. If the sticky traps are just as full after 3 weeks, there is a second source you have not found yet.

Our timeline, built from NC State’s stage lengths for a warm house. It assumes adults live a few days, as Insects Limited and PestWest say. If they live longer, as Michigan State says, the drop is slower, and a cool basement also takes longer.

Phorid flies from mushroom farms

If you live near mushroom farms in southeastern Pennsylvania and phorid flies pour in during late summer and fall, they are probably mushroom phorid flies, Megaselia halterata. Penn State Extension says these flies cannot breed in a house and die within 2 to 3 days indoors. So in this case, cleaning your drains will not help.

These flies breed in the compost of mushroom growing rooms. According to Penn State, numbers on the farms peak in September and October, and wind can carry the adults many miles. They fly to both natural and ultraviolet light. They also tend to climb, which is why they gather on upper floors and in attics, and they collect in humid rooms such as bathrooms. Penn State calls these events invasions rather than infestations, because the flies do not breed indoors.

The problem is real and current. The Pennsylvania Department of Agriculture says the fly destroys 10 to 40% of mushroom crops. In January 2025 it ordered farms in New Garden and Kennett townships to heat-treat their growing houses, a process called steaming off. In March 2026 the order grew to cover every mushroom farm in Chester County, as MyChesCo reported. On October 2, 2026, MyChesCo, citing CBS Philadelphia, reported New Garden residents saying the flies were swarming their homes again. One said she “probably had 1,000 come in” the year before.

Penn State gives residents this advice:

• Close windows and doors when you can, and close the blinds at night so lights do not draw them.
• Vacuum the flies off windows and bathroom walls.
• Use sticky traps on windows and light traps indoors.
• Avoid insecticides, since most of the flies die on their own. Any product you do use must be labeled for home use.

Questions about the farms go to the Pennsylvania Department of Agriculture, Bureau of Plant Industry, at 717-787-4843. Outside this region, a fall swarm with no source in the house is much less likely, so search the house first.

Coffin flies: where the name comes from

Coffin flies are phorid flies that breed on buried bodies, which is where the nickname comes from. Females of one species, Conicera tibialis, dig down through more than 2 meters (6.5 feet) of soil to reach a coffin, according to the Natural History Museum of Los Angeles County. They can then breed for several generations without coming back up.

NC State says the name also comes from their habit of breeding in mausoleums. Because of this, forensic scientists use phorid flies to help estimate how long a body has been dead. In a house, though, the name means nothing sinister. A “coffin fly” in your kitchen is the same fly that breeds in drain slime. At most, a sudden swarm in one room can point to a dead animal: Mississippi State lists carcasses such as a dead rat or bird among their breeding sites.

Coffin flies do not bite, and you get rid of them the same way as any other phorid fly: find the source and remove it.

Are any phorid flies useful?

Yes. Most phorid species live outdoors and have little impact on people, says Virginia Tech. Some even help. Since 1997, researchers have released 6 species of fire ant decapitating flies in the US to fight invasive fire ants, according to UF/IFAS. The first went out in Florida.

The way they work is grim. A female fly lays an egg inside a worker ant. The larva moves into the ant’s head and feeds there, and the head usually falls off. UF/IFAS says these flies are not drawn to people, pets, food or garbage, and you only find them around disturbed fire ant mounds. If fire ants are your real problem, see ourfire ant guide, which covers the two-step method for yards.

When to call someone

Most phorid fly problems end once you find a rotting source in the kitchen or a drain. Call a plumber if every drain tests clean and the flies are worst on the lowest floor. Call a pest professional if you still cannot find the source after 2 to 3 weeks of searching. If you rent, tell your landlord early.

• A plumber for a camera inspection or smoke test when the drains test clean, the flies come up near the floor, and they have lasted for months.
• A licensed pest professional when the source may be in a wall void or crawl space, or a dead animal you cannot reach. NC State also advises calling one quickly for restaurants, hospitals and other food or care settings.
• Your landlord or building manager in an apartment, since drain lines and walls are shared and the flies may come from another unit.
• A doctor the same day if you see maggots in a wound.
• Penn State Extension or the Pennsylvania Department of Agriculture for mushroom fly swarms in southeastern Pennsylvania.

Not sure they are phorid flies at all? A sharp photo of one on a sticky trap is enough for our bug identifier by picture. You can also compare them with the other tiny dark insects in our guide to small black bugs in the house.

Pest control disclaimer. Photo-based identification can help, but it is not always perfect. For dangerous spiders, large infestations, or anything you are unsure about, contact a licensed pest control professional.