There are thousands of fly species, but only a few are common pests in and around the home, and the eighteen in this guide cover almost everything you will meet in a house in the United States. The useful question is not how many flies exist. It is which one is in your kitchen, and what that particular one means.
Flies are usually sorted by family, which is no help at all when there is one buzzing at the window. This guide groups them by where you meet them and what causes them, because that is what determines the fix. Filth flies come from decaying organic material you can find and remove. Small indoor nuisance flies come from a specific damp source, most often fermenting fruit or an overwatered plant pot. Drain and moisture flies live in a film inside your plumbing. Biting flies come from water, usually water you do not own. Which of the eighteen are relevant where you live is covered in the Season and Region lines on each entry.
Getting the group right matters more than getting the species exactly right, because the four groups respond to four completely different measures. Spraying does not solve a cluster fly problem, cleaning the kitchen does not solve a drain fly problem, and nothing you apply to your yard will end horse fly season. Every biology and disease claim below is cited to an extension service, a public health agency or peer-reviewed work, because a good deal of what is published about flies is wrong.
How Many Types of Flies Are There?
Thousands of species, about a dozen that matter to you
Of the thousands of species of flies, only a few are common pests in and around the home. The ones that reach that short list share a habit rather than a family: they either develop in something we generate, such as waste, food or damp organic matter, or they need our blood. Everything else stays outdoors and never becomes your problem. That is why this guide covers eighteen species rather than a taxonomy, and why some famous flies are absent.
What all of them have in common
Every fly here goes through complete metamorphosis with egg, larva, pupa and adult stages. The larva, not the adult, is the stage worth targeting. Females deposit eggs in material where the larvae can develop, the larvae pass through three stages, then pupate inside a hardened shell before the adult emerges. Development speed is temperature dependent, and under optimal summer conditions some species go from egg to adult in as little as seven days. That is the whole reason a fly problem seems to appear overnight: it did not, but a week is short enough to feel like it.
Quick Identification Table
Eighteen species at a glance. Scroll the table sideways on a phone. Every row links to the full entry below.
| Species | Size | Color | Where you find it | Bites | Risk |
|---|---|---|---|---|---|
| House Fly | Less than 3/8 inch long | Gray, with four dark stripes down the thorax | Kitchens, bins, pet waste, compost, anywhere warm and organic | No | Contamination |
| Little House Fly | About two thirds the size of a house fly | Gray, without the house fly's thoracic stripes | Patios, entryways, garages and porches, hovering rather than landing | No | Nuisance |
| Blow Fly or Bluebottle | 1/8 to 5/8 inch long | Shiny metallic green or blue, often mixed with copper | Carrion, pet waste, and food waste in bins | No | Contamination |
| Flesh Fly | 9 to 13 mm, about a third to half an inch | Light gray with three black thoracic stripes and a reddish abdominal tip | Carrion and decaying matter outdoors, rarely indoors | No | Contamination |
| False Stable Fly | About 3/8 inch long, stouter than a house fly | Dark gray with a dull reddish mark on the back | Spoiled food, excrement and decaying vegetable matter | No | Contamination |
| Cluster Fly | About 3/8 inch, larger and more sluggish than a house fly | Dark, with short golden hairs on the thorax | Attics, wall voids, and sunny south and west walls | No | Nuisance |
| Fruit Fly or Vinegar Fly | About 0.12 inch, roughly 3 mm | Tan to amber with red eyes | Ripe and fermenting fruit, recycling, drains, and anywhere sugar ferments | No | Contamination |
| Fungus Gnat | About 1/16 to 1/8 inch long | Dark and slender, with long legs and antennae longer than the head | Potted houseplants, damp potting mix, and overwatered containers | No | Nuisance |
| Picture-Winged Fly | House fly sized | Distinctive dark band patterning on the wings | Around windows, in early autumn | No | Nuisance |
| Drain Fly or Moth Fly | 1/5 to 1/6 inch long | Fuzzy, dark or grayish, body and wings densely covered with hairs | Drains, floor drains, septic systems, and anywhere a wet organic film builds up | No | Nuisance, indicates a dirty drain |
| Phorid Fly | Roughly 1/32 to 1/4 inch long | Small and dark, with a characteristic hump on the thorax | Drains, but also broken sewer lines, damp soil under slabs, and decaying organic matter | No | Contamination, may indicate a broken line |
| Mosquito | Small and slender, with a long piercing proboscis | Gray to brown, narrow body, two wings | Anywhere within flying range of standing water | Yes, females only | Bite, and a genuine disease vector |
| Horse Fly | 14 to 19 mm long | Grayish-brown thorax, clear wings, large iridescent eyes | Open ground near water, pasture edges, trail sides | Yes, females only | Bite, painful |
| Deer Fly | 10 to 13 mm long | Greenish-yellow thorax with dark stripes, smoky or patterned wings | Near creeks, streams and wet ground, often along trails | Yes, females only | Bite, tularemia risk |
| Black Fly | About 1/16 inch | Stout, dark, rounded back with broad wings and short legs | Near rivers, streams and any fast-moving water | Yes, females only | Bite |
| Biting Midge | Less than 1/16 inch, about 1.6 mm | Dark gray to black | Salt marshes, and inland in tree holes and fresh water margins | Yes, females only | Bite |
| Stable Fly | House fly sized, with a bayonet-like proboscis | Gray, without the house fly's four thoracic stripes | Near livestock, and around compost and grass clipping piles | Yes, both sexes | Bite, painful |
| Sand Fly | Wings less than 3 mm long | Small, silvery-brown, long-legged, with densely hairy wings held in a V | Live oak forest and organic-rich soil in the southeastern United States | Yes | Bite, southern states only |
- Fruit fly, 3 mm
- Phorid fly, 3 mm
- Fungus gnat, 4 mm
- Biting midge, 2 mm
- Drain fly, 4 mm
- Little house fly, 5 mm
- House fly, 7 mm
- Stable fly, 7 mm
- Blow fly, 11 mm
- Horse fly, 19 mm
Filth and Nuisance Flies
Filth flies develop in decaying organic material, and none of them bite. They matter because they move between waste and food, carrying disease agents picked up while feeding and depositing them where you eat. The shared fix is the same for every species in this group and it is not insecticide: find and remove the material the larvae are developing in. Eliminating larval habitat is the preferred method of suppression, and chemical treatment is no substitute for it. If you have found the larvae themselves, our guide to guide to where maggots come from shows what the larval stage looks like and where it hides, and our fly control service handles sources inside a wall or crawl space.
House Fly
Musca domestica
- Size
- Less than 3/8 inch long
- Color
- Gray, with four dark stripes down the thorax
- Where you find it
- Kitchens, bins, pet waste, compost, anywhere warm and organic
- Bites
- No
- Season
- Greatest numbers in the hotter summer months
- Region
- Throughout the United States, and the fly most often found inside homes
House flies are less than 3/8 inch long with four dark stripes down the thorax[1]. They have sponging mouthparts, liquefying solid food with saliva and regurgitating onto it. Because those mouthparts sponge rather than pierce, a house fly cannot bite.
Females lay several batches of about 100 to 150 eggs in warm, moist organic material[1], with lifetime output of 350 to 900 eggs, the maggot emerging in 8 to 20 hours and the larva completing three stages in 3 to 7 days[2]. In optimal summer conditions the whole cycle finishes in as little as 7 days. For what the larval stage looks like, see our guide to where maggots come from.
House flies carry disease agents picked up on feces or kitchen waste and deposit them onto food[1], including organisms causing diarrhea, cholera, food poisoning, dysentery and eye infections. A 2023 review found individual flies carrying up to 400 bacterial taxa[3].
EcoGuard Professional Insight
The pattern we see most often is a clean kitchen with a fly problem the homeowner cannot explain, and nine times out of ten it is the bin rather than the room. Liquid escapes through a pinhole in the liner, collects in the seam at the bottom of the can, and stays warm and damp between collections. The kitchen passes any inspection you like while a breeding site sits inside the container. When we get called back to a house that has already been sprayed twice, the first thing we do is lift the liner out and look underneath, and that is usually the end of the mystery.
Little House Fly
Fannia canicularis
- Size
- About two thirds the size of a house fly
- Color
- Gray, without the house fly's thoracic stripes
- Where you find it
- Patios, entryways, garages and porches, hovering rather than landing
- Bites
- No
- Season
- Most numerous in the cooler spring and autumn months
- Region
- Throughout the United States, most noticeable around poultry houses, stables and compost
If a fly circles a porch at head height and never lands, it is probably not a house fly. Little house flies are about two thirds the size of a house fly, lack its thoracic stripes, and at rest hold their wings directly over the back rather than in the house fly's V[1].
The hovering is mating behavior. Males form aggregations in still air out of direct sun, usually five or six feet up, at adult head height[1]. They do not tolerate high daytime temperatures and are most numerous in the cooler spring and autumn months. Larval development happens in animal waste, especially poultry manure, and in fermenting clippings and compost.
Little house flies are far less of a health concern than house flies, and are not considered significant carriers of human disease agents. They also ignore the baits and traps that work on house flies, which is why a porch fly trap does nothing. A fan breaks up the swarm; removing damp clippings removes the source.
Blow Fly or Bluebottle
Family Calliphoridae
- Size
- 1/8 to 5/8 inch long
- Color
- Shiny metallic green or blue, often mixed with copper
- Where you find it
- Carrion, pet waste, and food waste in bins
- Bites
- No
- Season
- Warm months outdoors, with some entering homes in autumn
- Region
- Throughout the United States
Blow flies are unmistakable once you know to look for the color: shiny metallic green or blue, often mixed with copper[1], and running 1/8 to 5/8 inch long[4]. They are the flies that arrive first and in numbers.
The name comes from the association with carrion, and they do develop in decaying animal carcasses such as rodents, as well as discarded protein-rich organic matter in garbage. In the urban environment the most common developmental site is human food waste, with accumulations of pet waste also producing them. Under ideal temperatures they can develop from egg to adult in as little as 7 days. Like house flies they have sponging mouthparts and do not bite or feed on blood.
Blow fly larvae leave the source to find drier ground for pupation, which is why maggots crawl out of a backyard trash can when kitchen waste was not bagged[1]. And hanging sticky fly ribbons do not work on them, because unlike house flies they do not regularly rest on vertical surfaces[1].
Flesh Fly
Family Sarcophagidae
- Size
- 9 to 13 mm, about a third to half an inch
- Color
- Light gray with three black thoracic stripes and a reddish abdominal tip
- Where you find it
- Carrion and decaying matter outdoors, rarely indoors
- Bites
- No
- Season
- Warm months
- Region
- Throughout the United States, far more often outdoors than in
Flesh flies are larger than house flies, 9 to 13 mm long, typically light gray with three black stripes on the thorax[5]. The abdominal end is red in both males and females, which together with the stripes is the quickest field identification.
Flesh fly reproduction is unusual and worth knowing. Flesh flies are ovoviviparous: the larvae hatch inside the female and are held until a suitable site is found, then released in a process called larviposition[5]. That skips the egg stage entirely and gives them a head start on any competing species. About five days after larviposition the larvae are already in their third instar and nearly ready to pupate, pupation begins roughly a week after larviposition at 77 degrees Fahrenheit, and adults emerge about 10 days after pupation[5].
Flesh flies develop in carrion, including wildlife carcasses. Flesh flies indoors mean what blow flies indoors mean: something has died in a wall, attic or crawl space. They do not bite, and finding the carcass is the treatment. Surface spraying is no substitute.
False Stable Fly
Muscina stabulans
- Size
- About 3/8 inch long, stouter than a house fly
- Color
- Dark gray with a dull reddish mark on the back
- Where you find it
- Spoiled food, excrement and decaying vegetable matter
- Bites
- No
- Season
- Warm months
- Region
- Throughout the United States, usually an occasional indoor visitor rather than an infestation
The false stable fly earns its place here entirely on the strength of its name. It is about 3/8 inch long with a dull reddish mark on the back[6], larger and stouter than a house fly, and it is routinely mistaken for the true stable fly, which does bite.
The false stable fly does not bite. It has sponging mouthparts, the same equipment a house fly has. If something that looks like a large house fly bit you, it was a true stable fly, which carries a rigid forward-pointing proboscis you can see with the naked eye.
Females lay eggs in tainted foods, excrement, and the dead bodies of insects, snails and vertebrates. That last item matters: like blow flies and flesh flies, a sudden indoor population can point at a dead animal rather than at the kitchen. Treatment is the same as for any filth fly, which is to find and remove the material they are developing in rather than to treat the adults.
Cluster Fly
Pollenia rudis and relatives
- Size
- About 3/8 inch, larger and more sluggish than a house fly
- Color
- Dark, with short golden hairs on the thorax
- Where you find it
- Attics, wall voids, and sunny south and west walls
- Bites
- No
- Season
- Enters buildings in autumn, reappears on warm days in early spring
- Region
- Throughout the United States wherever earthworms are common, since the larvae are parasites of earthworms
Cluster flies are larger and more sluggish than the common house fly, about 3/8 inch, with short golden hairs on the thorax. To most people they have no obvious feature distinguishing them from an ordinary house fly, which is why they get treated as one and the treatment fails.
The life cycle is the reason. Cluster fly larvae develop as parasites inside earthworms[4], outdoors in soil, with up to four generations each summer[7]. None of that happens inside your house, so there is no indoor breeding site to find and no sanitation problem to fix.
In autumn the last generation seeks protected places to overwinter, invading attics and getting under siding and around windows. On warm days in early spring they move outdoors and cover the sunny side of houses. They do not damage buildings, furniture or occupants, and are only using the house to spend winter. The fix is exclusion, done before they arrive.
EcoGuard Professional Insight
Timing is everything with cluster flies and most people get it wrong by about two months. Once they are in the wall void in November, sealing the gaps traps them inside, and warm days will keep pushing them into the living space until spring. The work has to happen in late summer, before the autumn movement starts: seal around window frames, under siding, at soffit and fascia junctions and around roof penetrations. Homeowners who call us in October usually want the attic sprayed, and what we actually recommend is a vacuum for the ones already inside and an exclusion appointment for next August.
Small Indoor Nuisance Flies
Small, harmless and easy to confuse with one another. None of these bite and none carry the contamination risk of a filth fly, but all three are commonly misidentified, which sends people after the wrong fix. The shared cause is a specific moist source rather than general untidiness: fermenting fruit, overwatered potting soil, or in one case nothing indoors at all. Identify which one you have before you treat anything, because the three respond to completely different measures.
Fruit Fly or Vinegar Fly
Drosophila melanogaster
- Size
- About 0.12 inch, roughly 3 mm
- Color
- Tan to amber with red eyes
- Where you find it
- Ripe and fermenting fruit, recycling, drains, and anywhere sugar ferments
- Bites
- No
- Season
- Peaks in late summer and autumn with the fruit harvest
- Region
- Throughout the United States, anywhere fruit ripens or ferments indoors
Fruit flies, more precisely vinegar flies, are small tan to amber flies with red eyes, about 0.12 inch long, and the larvae are small white legless maggots up to 0.2 inch long when mature[8]. The red eyes are visible with a hand lens and settle identification against fungus gnats and phorid flies immediately.
The numbers explain why they seem to appear from nothing. A female lays 700 to 800 eggs in a life span of 7 to 8 days in summer and 20 to 30 days at other times, and development is ideal in the low 80s Fahrenheit[9]. Larvae develop in very ripe, damaged and fermenting fruit. One overlooked tomato can produce a visible population inside a two weeks.
Control is sanitation, and the target is fermentation rather than food generally. Refrigerate ripe produce, rinse recycling, and check under and behind things. To tell them apart from gnats, see our comparison of gnats and fruit flies and where fruit flies come from, and a longer piece on where they come from in the first place.
EcoGuard Professional Insight
The source is almost never the fruit bowl, because that is the first place people look and clean. In our experience the productive spots are the ones nobody moves: the lip under the rim of a recycling bin, the gap between the dishwasher and the cabinet where something spilled, the drip tray under a water dispenser, and the mop bucket in the garage. We have also traced infestations to a bag of potatoes in a low cupboard more than once. If the kitchen has been cleaned twice and the flies are still there, stop cleaning surfaces and start moving appliances.
Fungus Gnat
Families Sciaridae and Mycetophilidae
- Size
- About 1/16 to 1/8 inch long
- Color
- Dark and slender, with long legs and antennae longer than the head
- Where you find it
- Potted houseplants, damp potting mix, and overwatered containers
- Bites
- No
- Season
- Year round indoors, worst in winter when houseplants are overwatered
- Region
- Throughout the United States, indoors year round; watering habits rather than climate decide it
Fungus gnat adults are about 1/16 to 1/8 inch long with slender legs and segmented antennae longer than their head, and wings that appear light gray to clear[10]. The larvae are distinctive if you look closely at the soil surface: a shiny black head on an elongated, whitish to clear, legless body.
Fungus gnats are a moisture problem wearing an insect costume. Larvae feed on organic mulch, leaf mold, grass clippings, compost, root hairs and fungi, and a generation from female to female can be produced in about 17 days depending on temperature.
Adult fungus gnats do not damage plants or bite people, and are primarily a nuisance. The control follows from the biology: because they thrive in moist conditions, avoid overwatering, provide good drainage, and let container soil dry between waterings. Insecticide on a plant that is still overwatered accomplishes nothing. On whether the small flies around your plants bite, see our piece on whether gnats bite humans.
Picture-Winged Fly
Ceroxys latiusculus
- Size
- House fly sized
- Color
- Distinctive dark band patterning on the wings
- Where you find it
- Around windows, in early autumn
- Bites
- No
- Season
- Early autumn only; those that enter are usually dead by the end of November
- Region
- Local and sporadic rather than widespread, turning up as an occasional autumn invader
Picture-winged flies are house fly sized with distinctive dark band patterning on the wings, which is where the name comes from and which makes them one of the easier flies in this guide to identify from across a room.
Picture-winged flies are a common invader of homes in early autumn, often found around windows. Unlike cluster flies, which settle in for the winter, Ceroxys latiusculus does not survive indoors through winter, and those that do enter buildings are usually all dead by the end of November.
The larvae develop within the stems of Senecio, native plants in the aster and sunflower family, which means there is no indoor breeding site and nothing in the house to find. They are a harmless seasonal nuisance rather than a health hazard, they do not bite, and they do not contaminate food the way a filth fly does. The only sensible response is a vacuum and, if the numbers are annoying enough to bother with, the same autumn exclusion work that keeps cluster flies out.
Drain and Moisture Flies
These two species live in wet organic film rather than in food waste, which is why they survive every kitchen clean and come back within the week. The larvae develop in the muck and slime that accumulates inside pipes and in moist decaying matter around leaks. The shared fix is mechanical: the film has to be physically removed from the pipe wall, or digested by an enzymatic product given hours of contact. If a problem persists after that, the next call is a plumber, not a pest company.
Drain Fly or Moth Fly
Family Psychodidae
- Size
- 1/5 to 1/6 inch long
- Color
- Fuzzy, dark or grayish, body and wings densely covered with hairs
- Where you find it
- Drains, floor drains, septic systems, and anywhere a wet organic film builds up
- Bites
- No
- Season
- Year round indoors, since the habitat is climate controlled
- Region
- Throughout the United States, indoors year round; plumbing condition rather than climate decides it
Drain flies are 1/5 to 1/6 inch long, fuzzy and dark or grayish, body and wings densely covered in hairs, with the wings often held roof-like over the body at rest[11]. That is where the name moth fly comes from.
The habitat is the whole key to control. Larvae grow and feed in polluted shallow water or highly moist organic solids, in the bacterial muck, slime or gelatinous film accumulating in drains. Eggs hatch in 32 to 48 hours at 70 degrees Fahrenheit, larvae mature in 9 to 15 days, and the full cycle takes one to three weeks[11]. They do not bite humans.
Because the larvae live in a film bonded to the pipe wall, anything poured down the drain runs past them. The film has to come off physically with a stiff drain brush, or be digested by an enzymatic or bacterial product given hours of undisturbed contact. Their larvae are considered useful organisms in cleaning sewage water, which shows how well adapted they are.
EcoGuard Professional Insight
The tape test settles a drain fly argument in one night. Put a strip of clear packing tape sticky side down across the drain opening, leaving a gap at one edge for airflow, and check it in the morning. Adults emerging from the pipe stick to it, and you will know within a day which of several drains is actually producing them rather than guessing. We use this before we treat anything, because in a house with a kitchen sink, a laundry standpipe, two bathroom sinks and a floor drain, treating all five is wasted work and treating the wrong one looks like a treatment failure.
Phorid Fly
Family Phoridae, also called scuttle or humpbacked flies
- Size
- Roughly 1/32 to 1/4 inch long
- Color
- Small and dark, with a characteristic hump on the thorax
- Where you find it
- Drains, but also broken sewer lines, damp soil under slabs, and decaying organic matter
- Bites
- No
- Season
- Year round indoors
- Region
- Throughout the United States, indoors year round; an older or damaged sewer lateral is the risk factor
Phorid flies, also called scuttle, humpbacked and coffin flies, are roughly 1/32 to 1/4 inch long and breed in moist, decaying organic matter[12]. In profile they carry a characteristic hump on the thorax, the reliable way to separate them from the fruit flies they are mistaken for. The other tell is behavioral: they run across a surface in short bursts rather than fly.
Total developmental time from egg through the pupal stage is approximately 10 days, so a population builds quickly once a source establishes. They do not bite.
Phorid flies matter because of where they breed. Unlike drain flies, largely confined to the film inside a pipe, phorids exploit soil saturated by a leak. NC State points at plumbing: if lines have fractured a reputable plumbing company should examine them, and a break under a slab means opening the concrete to repair the pipe[12]. A persistent phorid problem that survives thorough drain cleaning is a plumbing diagnosis.
EcoGuard Professional Insight
A phorid fly problem that comes back after the drains have genuinely been cleaned is the one case where we tell a homeowner to call a plumber before booking us again. The pattern is recognisable: flies concentrated in one room, often a ground-floor bathroom or a slab-on-grade kitchen, a musty smell that outlasts the cleaning, and sometimes a patch of floor that never quite dries. What is feeding them is soil under the slab saturated by a cracked lateral, and no amount of drain treatment reaches it. Spending money on repeat fly treatments before the pipe is found is money spent twice.
Biting Flies
These are the flies that draw blood, and in every species here it is the female that bites. They share a cause that has nothing to do with sanitation: almost all of them develop in water or saturated ground, often well off your property. That means the fix is rarely a spray. It is draining or emptying standing water where you control it, covering skin near water at the times these flies are active, and accepting that a creek or a neighboring pasture is beyond any treatment. Our mosquito control service and fly control service can help with the water you own.
Mosquito
Family Culicidae
- Size
- Small and slender, with a long piercing proboscis
- Color
- Gray to brown, narrow body, two wings
- Where you find it
- Anywhere within flying range of standing water
- Bites
- Yes, females only
- Season
- Late spring through early fall, peaking in warm weather
- Region
- Throughout the United States, anywhere water stands long enough for larvae to develop
Mosquitoes are flies, in the same order as house flies. The mouthparts settle it: a mosquito carries a long, slender proboscis adapted for piercing skin and sucking blood, where a house fly has a sponging pad and cannot bite at all.
Only female mosquitoes feed on blood. Larvae develop in standing water, including ponds, bird baths and any other object that holds water, and in summer the entire cycle from egg to adult can finish in a week or less depending on water temperature. That speed is why a forgotten saucer under a plant pot turns into a mosquito problem inside a two weeks.
Mosquitoes are the one genuine disease risk in this guide for most homeowners. Malaria is transmitted by Anopheles mosquitoes[13], and dog heartworm is transmitted by mosquito bites[14]. Control is almost entirely water: drain it, empty it weekly, or keep it moving. For a persistent problem, our guide to getting rid of mosquitoes covers the treatment sequence, and our mosquito control service handles standing water you cannot reach.
Horse Fly
Family Tabanidae
- Size
- 14 to 19 mm long
- Color
- Grayish-brown thorax, clear wings, large iridescent eyes
- Where you find it
- Open ground near water, pasture edges, trail sides
- Bites
- Yes, females only
- Season
- Most emerge between May and August
- Region
- Throughout the United States, concentrated near wet ground, flood plains and pasture
Horse flies are the largest biting flies most people meet, running 14 to 19 mm long with a grayish-brown thorax and clear wings[15]. The eyes are the giveaway at close range: banded and iridescent, and set far wider than any house fly.
Female tabanids are persistent blood-feeding pests; males do not feed on blood at all. Young larvae crawl or drop into water or wet soil, where they develop over an extended period, so the adults you meet are almost always within reach of a flood plain, a creek edge or an irrigated pasture. They are abundant along hiking trails, narrow lanes and woodland edges.
The bite is painful because the mouthparts tear rather than pierce cleanly. Horse flies are suspected vectors of livestock diseases, and their intermittent feeding makes tabanids agents of disease transmission worth taking seriously, with bite sites able to become secondary infections. There is no practical way to treat an open landscape for them. Long sleeves, repellent, and avoiding the wettest ground at midday do more than any spray.
EcoGuard Professional Insight
Horse fly and deer fly calls are the ones we most often have to turn down, and it is worth saying plainly. These flies breed in wet soil and standing water that is usually well off the property, sometimes a quarter mile away, and there is no perimeter treatment that changes that. What we can do is find and fix the water on your own property that is contributing, and tell you honestly when the source is a neighboring field or a creek. A company that promises to spray your yard and end horse fly season is selling you something that does not work.
Deer Fly
Genus Chrysops
- Size
- 10 to 13 mm long
- Color
- Greenish-yellow thorax with dark stripes, smoky or patterned wings
- Where you find it
- Near creeks, streams and wet ground, often along trails
- Bites
- Yes, females only
- Season
- Most emerge between May and August
- Region
- Throughout the United States, concentrated near creeks, streams and other wet ground
Deer flies are smaller cousins of the horse fly, 10 to 13 mm long, with a greenish-yellow thorax marked by dark stripes and wings that are tinted smoky gray-brown or carry a dark pattern[15]. The patterned wing is the quickest way to separate a deer fly from a horse fly in the field.
As with horse flies, only females take blood, and the larvae develop in water or wet soil. They circle the head persistently, which is why a short walk near a creek in June can feel like an ambush.
Deer flies matter more than their size suggests. The CDC names deer fly bites, alongside tick bites, as a common source of tularemia infection in the United States[16]. That is a real if uncommon risk, and it is the reason we describe deer flies as a bite risk rather than a nuisance. Cover exposed skin near water in early summer, and treat a bite that develops an ulcer or swollen glands as a reason to see a doctor.
Black Fly
Family Simuliidae
- Size
- About 1/16 inch
- Color
- Stout, dark, rounded back with broad wings and short legs
- Where you find it
- Near rivers, streams and any fast-moving water
- Bites
- Yes, females only
- Season
- Active spring through summer, with bites most common in spring
- Region
- Throughout the United States along rivers and fast-moving streams, which the larvae require
Black flies are small, about 1/16 inch, stout and dark with a distinctly rounded back, broad wings and short legs[17]. The humped profile is where the common name buffalo gnat comes from.
Only female black flies bite. Eggs are laid in rivers, streams and other running water, and the larvae attach themselves to stones, grass, branches and other objects under the water. That requirement for moving, oxygenated water is the single most useful fact about them: black flies cannot breed in a bird bath, a bucket or a pond, so a black fly problem is always a river problem.
Black flies are active spring through summer, and bites are most common in spring. Reactions range from small red spots with little irritation through to considerable irritation and swelling. In Minnesota, where they are well studied, black flies are not known to spread diseases. There is nothing to treat at a house. Long sleeves and avoiding the river corridor on still spring mornings is the honest advice.
Biting Midge
Family Ceratopogonidae, also called no-see-ums
- Size
- Less than 1/16 inch, about 1.6 mm
- Color
- Dark gray to black
- Where you find it
- Salt marshes, and inland in tree holes and fresh water margins
- Bites
- Yes, females only
- Season
- Warm months, most active at dawn and dusk
- Region
- Coastal marshland across the United States, with inland populations near fresh water
Biting midges are the smallest biting flies you will meet, less than 1/16 inch long and dark gray to black[18]. They are called no-see-ums because the bite registers before the insect does, and they pass through standard window screening.
Classic habitat is salt marsh, with some species developing inland in tree holes and other fresh water areas. They are an outdoor, edge-of-water problem tied closely to wind and time of day, and they drop off sharply in any real breeze.
The bites cause welts and intense itching out of all proportion to the insect's size. If you are trying to tell a midge bite from a mosquito bite, our comparison of no-see-um bites and mosquito bites walks through the differences. Fine-mesh screening, repellent and staying upwind are the practical measures; there is no yard treatment that meaningfully reduces them.
Stable Fly
Stomoxys calcitrans
- Size
- House fly sized, with a bayonet-like proboscis
- Color
- Gray, without the house fly's four thoracic stripes
- Where you find it
- Near livestock, and around compost and grass clipping piles
- Bites
- Yes, both sexes
- Season
- Appears mid to late spring, severe in early summer, declining in high summer heat
- Region
- Throughout the United States wherever livestock, horses or large compost piles are present
The stable fly is the reason people say a house fly bit them. It looks like a house fly except for two things: a bayonet-like proboscis protruding from the front of the head, and the absence of the four dark thoracic stripes that mark a true house fly.
Both sexes of stable fly feed on blood about once a day and give a painful bite[1]. Under optimal temperatures they develop from egg to adult in 12 days[1]. Beyond livestock manure, piles of moist decaying grass clippings, hay and silage are potential sources, and a backyard compost pile can be an ideal developmental site supplying an entire neighborhood.
Although stable flies can transmit some viruses, they are not known to be significant carriers of disease agents in the United States, nor to play a significant role in spreading human pathogens. The fix is the compost pile, not a spray.
Sand Fly
Genus Lutzomyia, subfamily Phlebotominae
- Size
- Wings less than 3 mm long
- Color
- Small, silvery-brown, long-legged, with densely hairy wings held in a V
- Where you find it
- Live oak forest and organic-rich soil in the southeastern United States
- Bites
- Yes
- Season
- Warm months, active at night
- Region
- Southern United States only, from Florida to Louisiana plus Arkansas, Tennessee and the Carolinas, and as far north as Maryland and Delaware
True sand flies are small, silvery-brown, long-legged flies with narrow bodies and densely hairy wings that give them a moth-like look, with wings under 3 mm long held erect above the body in a V. They are nocturnally active, and the larvae develop in terrestrial microhabitats rich in organic matter.
Sand flies that transmit disease are phlebotomines, and they spread Leishmania parasites. Lutzomyia shannoni is a proven vector of vesicular stomatitis virus and a suspected vector of visceral leishmaniasis and sand fly fever.
The documented United States range runs through the southern states from Florida to Louisiana plus Arkansas, Tennessee and the Carolinas, reaching as far north as Maryland and Delaware[19]. Outside that range, whatever is biting at dusk is a biting midge or a mosquito, not a sand fly.
Preventing Flies
Prevention for flies is unglamorous and it works. Three things do almost all of it: remove what the larvae develop in, close the ways adults get inside, and take away standing water and damp.
- 1kitchen bin
- 2fruit bowl and recycling
- 3sink and floor drains
- 4houseplant pots
- 5attic and wall voids
- 6crawl space
- 7compost and yard waste
- 8standing water
- 9pet waste
Sanitation is the whole game
Every filth fly on this page develops in organic material, and removing that material is the preferred method of suppression. Insecticides may knock down adults, but they are not a substitute for proper sanitation and aggressive elimination of developmental sites, and house flies have already developed resistance to many of the products registered against them. Remove and dispose of organic waste at least once a week, including dog feces, rotting fruit and kitchen waste. Bag trash before it goes in the bin, keep container lids closed, and wash the containers themselves out with soap and water periodically, because residue in the bottom seam is a breeding site even when the bin looks empty. Set bins out for collection weekly even when they are not full, since garbage sitting longer than a week is likely to produce adult blow flies.
Seal the ways in
Flies found inside a building have entered from outside in almost all cases, so barriers are the first line of defense. Seal cracks around windows and doors, and fit screens that actually meet their frames. For overwintering species the timing is what matters: cluster flies, blow flies and face flies crawl into cracks around siding, windows, vents and chimneys to get in, and once they are in the wall void, sealing traps them inside. Do exclusion work in late summer, before the autumn movement begins. Pay attention to the south and west walls, which are warmest in autumn and attract the most flies, and to soffit and fascia junctions, roof penetrations and utility entries.
Remove the water and the damp
Biting flies need water. Mosquito larvae develop in ponds, bird baths and any other object holding standing water, so anything that holds water for more than about a week is a breeding site: saucers under pots, tarps, gutters, wheelbarrows, pet bowls and clogged drains. Empty them weekly or remove them. Stable flies breed in moist decaying grass clippings, hay and silage, and a backyard compost pile can supply an entire neighborhood, so turn compost properly and spread clippings thin to dry. Indoors, fungus gnats are a watering problem before they are a pest problem: avoid overwatering, provide good drainage, and let the surface of container soil dry between waterings.
Managing an Indoor Fly Infestation
If flies are already inside, the order of operations matters. Identify the species, find and remove the source, and only then reach for a trap or a treatment.
Identify before you treat
The single biggest waste of effort in fly control is treating the wrong species. A porch fly trap does nothing for little house flies, which ignore the baits and traps that work on house flies. Vertically hanging sticky ribbons do not work on blow flies, because unlike house flies they do not regularly rest on vertical surfaces. Spraying an attic does not resolve cluster flies, which have no indoor breeding site. Cleaning the kitchen does not resolve drain flies, whose larvae live in a film bonded to the inside of a pipe. Work out which of the eighteen species you actually have, using the quick identification table above, then pick the measure that matches it.
Clean the source, not the surface
For filth flies, find the material the larvae are developing in and remove it. Lift bin liners out and check underneath, pull appliances forward, check under and behind pet feeding areas, and look at the floor beneath the can rather than the counter above it. For drain flies and phorid flies the source is inside the plumbing: run a stiff, long-handled drain brush as far down the pipe as it reaches and scrub the walls, and on a garbage disposal remove the splash guard and scrub both faces. Follow with an enzymatic or bacterial drain product applied at night so it gets hours of undisturbed contact. Bleach poured down a drain sheets through the middle of the pipe and past the film, which is why the flies come back.
Use traps as a supplement, never as the plan
Traps reduce adults; they do not touch the source, and a trap left running against an active breeding site simply catches flies forever. Match the trap to the species: sticky fly paper works on house flies that rest on vertical surfaces, odor-baited traps work on blow flies but should be placed well away from the building because they smell, and a simple vinegar or wine trap catches vinegar flies. For drain flies, clear packing tape placed sticky side down across a drain opening overnight, with a gap for airflow, tells you which drain is actually producing them before you treat anything. Do not use electrocuting traps near food preparation areas.
When to Call EcoGuard
Most fly problems are a source that has not been found yet, and most of them a homeowner can find with a flashlight and twenty minutes. Three situations are different, and they are the ones worth a call.
The first is a sudden indoor population of metallic blow flies or gray flesh flies with no food source anywhere near them, which usually means an animal has died inside a wall, an attic or a crawl space. The second is small flies that keep returning after the drains have genuinely been brushed and treated, which points at a fractured line under a slab. The third is autumn cluster fly pressure in an older house, where the work is exclusion sealing done in late summer on a schedule, not treatment in October.
Our fly control and mosquito control services cover inspection, source location and exclusion. If you are not sure which of the eighteen species above you have, send a photo and we will tell you what it is before we quote anything.
Fly Species FAQs
How do I identify what kind of fly I have?
Start with three things you can see without equipment: size, whether it bites, and where you found it. A fly under an eighth of an inch near fruit or a drain is a small nuisance fly; a fly with four dark stripes on a gray thorax at around three eighths of an inch is a house fly; anything metallic green or blue is a blow fly. If it bit you, it is not a house fly, a blow fly or a fruit fly, because all of those have sponging mouthparts and physically cannot bite. Where you found it narrows it further, since drain flies and phorid flies come out of plumbing and fungus gnats come out of potting soil.
Which flies actually bite?
In this guide, seven do: mosquitoes, horse flies, deer flies, black flies, biting midges, stable flies and sand flies. In every one of them it is the female that takes blood, and in most the male feeds on nectar and never bites at all. The filth flies, drain flies and small nuisance flies cannot bite. House flies have sponging mouthparts and cannot pierce skin, so if something that looked like a house fly bit you it was almost certainly a stable fly, which has a rigid forward-pointing proboscis you can see with the naked eye.
Do flies carry disease?
Some do, and the honest answer is more specific than the claims you will find online. House flies pick up disease agents while feeding on waste and deposit them on food, and are known to carry organisms causing diarrhea, cholera, food poisoning, dysentery and eye infections. Mosquitoes are genuine disease vectors. Deer fly bites are named by the CDC as a source of tularemia infection. What flies do not transmit is tuberculosis, which spreads through the air between people, or malaria, which is carried only by Anopheles mosquitoes. Stable flies are not known to be significant carriers of disease agents in the United States.
Why did so many flies appear suddenly?
Fly development is fast enough that a population can become visible in about a week. Under optimal summer conditions house flies and blow flies complete the whole cycle from egg to adult in as little as seven days, and a single female house fly lays batches of roughly 100 to 150 eggs. A sudden indoor appearance usually means one of three things: a breeding source reached maturity all at once, a batch of overwintering flies warmed up and became active, or something died in a wall or crawl space. Large numbers of metallic blow flies or gray flesh flies indoors with no food source points at the third.
What is the difference between a fruit fly and a gnat?
They are different insects with different sources. Fruit flies, properly vinegar flies, are tan to amber with visibly red eyes, about an eighth of an inch, and they breed in very ripe, damaged and fermenting fruit. Fungus gnats are darker, more slender, with long legs and antennae longer than the head, and they breed in damp potting soil where the larvae feed on organic matter and fungi. The practical difference is where you treat: fruit flies mean fermentation in the kitchen or recycling, fungus gnats mean you are overwatering a houseplant.
How do I tell a drain fly from a phorid fly?
Look at the shape and the movement. Drain flies are fuzzy, with the body and wings densely covered in hairs, and they hold their wings roof-like over the body at rest, which makes them look like tiny moths. Phorid flies are not hairy, have a distinct hump on the thorax when seen from the side, and characteristically run across a surface in short bursts rather than flying. The difference matters: drain flies live in the film inside the pipe, while phorid flies will also breed in soil saturated by a broken line under a slab, which is a plumbing repair rather than a drain cleaning.
Why do I get flies in the attic every spring?
That is the cluster fly pattern. Cluster flies do not breed indoors at all; their larvae develop as parasites inside earthworms, outdoors in soil. In autumn the last generation seeks somewhere protected to overwinter and invades attics, gets under siding and settles around windows. On warm days in early spring they become active again and are often seen covering the sunny side of a house, or pushing into living space through light fittings and window frames. Because there is no indoor breeding site, sanitation and spraying accomplish little. Exclusion sealing, done in late summer before they arrive, is what works.
Are maggots in my bin the same fly as the ones in my kitchen?
Often not. Maggots in an outdoor bin are usually house fly or blow fly larvae, since both readily develop in food waste and both can finish the cycle from egg to adult in about a week. Small flies hovering around a kitchen counter are more likely vinegar flies from fermenting produce, or fungus gnats from a plant pot, and neither of those produces the large cream-colored maggots people find in a bin. Blow fly larvae also leave their food to pupate somewhere dry, which is why homeowners find them crawling out of a trash can rather than sitting in it.
When should I call a professional about flies?
Three situations are worth a call rather than another round of cleaning. First, a sudden indoor population of metallic blow flies or gray flesh flies with no food source, which usually means an animal has died inside a wall, attic or crawl space. Second, small flies that persist after drains have genuinely been brushed and treated, which points at a fractured line under a slab. Third, autumn cluster fly pressure in an older house, where the work is exclusion sealing on a schedule rather than treatment. Recurring fly problems are almost always a source that has not been found.
About the author
General Manager and Termite Director, EcoGuard Pest Management
Vincent Villalobos is General Manager and Termite Director at EcoGuard Pest Management, where he's worked since 2017. He runs the crews, trains the techs, and writes here so homeowners know what they're looking at and what actually works.
References
- UC IPM. “Pest Notes: Flies.” UC ANR Publication 7457, University of California Statewide IPM Program. Accessed September 25, 2026. https://ipm.ucanr.edu/home-and-landscape/flies/
- University of New Hampshire Extension. “House Fly [fact sheet].” Accessed September 25, 2026. https://extension.unh.edu/resource/house-fly-fact-sheet
- Nayduch, D., Neupane, S., Pickens, V., Purvis, T. and Olds, C. “House Flies Are Underappreciated Yet Important Reservoirs and Vectors of Microbial Threats to Animal and Human Health.” Microorganisms, vol. 11, no. 3, 2023, article 583. PubMed Central. Accessed September 25, 2026. https://pmc.ncbi.nlm.nih.gov/articles/PMC10054770/
- Purdue University Extension Entomology. “Fly Control Around the Home.” Publication E-7. Accessed September 25, 2026. https://extension.entm.purdue.edu/publications/E-7/E-7.html
- Diaz, L. A. and Kaufman, P. E. “A Flesh Fly, Sarcophaga crassipalpis Macquart.” EENY-503/IN905, University of Florida IFAS Extension. Accessed September 25, 2026. https://ask.ifas.ufl.edu/publication/IN905
- University of Minnesota Extension. “Flies.” Accessed September 25, 2026. https://extension.umn.edu/nuisance-insects/flies
- University of New Hampshire Extension. “Cluster Flies [fact sheet].” Accessed September 25, 2026. https://extension.unh.edu/resource/cluster-flies-fact-sheet
- UC IPM. “Vinegar Fly.” UC IPM Pest Management Guidelines: Fig, UC ANR Publication 3447, University of California. Accessed September 25, 2026. https://ipm.ucanr.edu/agriculture/fig/vinegar-flies/
- UC IPM. “Vinegar Fly.” UC IPM Pest Management Guidelines: Strawberry, UC ANR Publication 3468, University of California. Accessed September 25, 2026. https://ipm.ucanr.edu/agriculture/strawberry/vinegar-fly/
- UC IPM. “Pest Notes: Fungus Gnats.” UC ANR Publication 7448, University of California Statewide IPM Program. Accessed September 25, 2026. https://ipm.ucanr.edu/home-and-landscape/fungus-gnats/
- Lyon, W. F., revised by Shetlar, D. “Drain Flies (Moth Flies).” ENT-41, Ohio State University College of Food, Agricultural, and Environmental Sciences. Accessed September 25, 2026. https://cfaes.osu.edu/fact-sheet/drain-flies-moth-flies
- Crawley, S. and Bertone, M. “Phorid Flies.” NC State Extension Publications. Accessed September 25, 2026. https://content.ces.ncsu.edu/phorid-flies
- Centers for Disease Control and Prevention. “About Malaria.” Accessed September 25, 2026. https://www.cdc.gov/malaria/about/index.html
- Centers for Disease Control and Prevention. “About Dirofilariasis.” Accessed September 25, 2026. https://www.cdc.gov/dirofilariasis/about/index.html
- Waldvogel, M. and Apperson, C. “Horse Flies and Deer Flies.” NC State Extension Publications. Accessed September 25, 2026. https://content.ces.ncsu.edu/horse-flies-and-deer-flies
- Centers for Disease Control and Prevention. “How Tularemia Spreads.” Accessed September 25, 2026. https://www.cdc.gov/tularemia/causes/index.html
- University of Minnesota Extension. “Black flies and gnats.” Accessed September 25, 2026. https://extension.umn.edu/nuisance-insects/black-flies
- Pitzer, J. B., Koehler, P. G. and Diclaro, J. W. II. “Biting Flies.” ENY-220/IG081, University of Florida IFAS Extension. Accessed September 25, 2026. https://ask.ifas.ufl.edu/publication/IG081
- Mann, R. S., Kaufman, P. E. and Butler, J. F. “A Sand Fly, Lutzomyia shannoni Dyar.” EENY-421/IN797, University of Florida IFAS Extension. Accessed September 25, 2026. https://ask.ifas.ufl.edu/publication/IN797
How we made this article
We researched and drafted this article with the help of AI tools, which let us gather and organize findings from many scientific sources quickly. People made the final call on every fact: each statistic and health or safety claim was checked against the primary sources listed above, and the full article was reviewed for accuracy by Vincent Villalobos, EcoGuard's General Manager and Termite Director. The illustrations in this article are AI-generated, not photographs.
