Most flies you find indoors belong to one of six or seven common species, and identifying which one you’re dealing with is the fastest way to get rid of them. Each type breeds in a different spot, so the fix for fruit flies (overripe bananas on the counter) is completely different from the fix for drain flies (gunk buildup inside pipes). Here’s how to tell them apart and what to do about each one.
House Flies
The common house fly is the one most people picture: gray, slightly smaller than three-eighths of an inch, with four dark stripes running down its upper back. House flies can’t bite. They have sponge-like mouthparts and eat solid food by liquefying it with saliva first, which is part of what makes them so effective at spreading bacteria. They can mechanically transmit salmonella, cholera, and shigella by landing on contaminated material and then landing on your food or kitchen surfaces.
House flies breed in garbage, animal waste, compost, and decaying organic matter. A female lays eggs that hatch in as little as 8 to 20 hours. The larvae (maggots) develop through three stages in 3 to 7 days under warm conditions, then pupate. The adult emerges anywhere from three days to four weeks later depending on temperature. That fast lifecycle means a small problem becomes a big one quickly if the breeding source isn’t removed. Keeping trash sealed, cleaning up pet waste, and making sure door and window screens are intact will handle most house fly issues.
Fruit Flies
Fruit flies are tiny, about an eighth of an inch, with distinctive red eyes. If you see small flies hovering around your kitchen counter, fruit bowl, or recycling bin, these are almost certainly the culprit. They’re sometimes called vinegar flies because they’re drawn to anything fermenting: overripe bananas, rotting onions or potatoes, spilled juice, wine, beer, or apple cider vinegar.
The larvae feed on yeasts associated with decaying fruit and vegetables, so any forgotten produce is a potential breeding ground. They also thrive in less obvious spots like the residue under kitchen appliances, inside recycling bins, around soft drink dispensers, and even in cracked tile or flooring where sugary liquids have seeped. Getting rid of them means eliminating every fermenting food source. Throw out overripe produce, clean under appliances, rinse bottles before recycling, and wipe down surfaces. You can trap adults with a small dish of apple cider vinegar covered in plastic wrap with a few holes poked in it, but the infestation won’t stop until you remove whatever they’re breeding in.
Drain Flies
Drain flies are fuzzy, moth-like flies about the size of a fruit fly. They have broad, leaf-shaped wings covered in tiny hairs, and they tend to rest on walls near sinks, showers, or floor drains. If you see them mostly in bathrooms or near kitchen sinks, the breeding site is almost certainly inside your drain pipes.
Their larvae feed on the slimy organic film (a mix of fats, oils, grease, and bacteria) that builds up on the inside walls of pipes. Killing the adults alone won’t solve the problem because more will keep emerging from the drain. For a mild case, a metal scrub brush pushed as far down the drain as it will reach can physically scrape away the buildup where larvae live. For more serious infestations, a commercial drain cleaner designed for organic buildup works by breaking down or digesting the film throughout the entire pipe. Standard chemical drain cleaners meant for clogs aren’t the same thing and won’t necessarily remove the biofilm that drain flies depend on.
Fungus Gnats
If the tiny flies in your house seem to cluster around your houseplants rather than your kitchen, they’re likely fungus gnats. These are small, dark, mosquito-like flies with noticeably long antennae and a distinctive forked vein pattern on their wings. They’re weak fliers and tend to hover close to the soil surface of potted plants.
Fungus gnat larvae live in moist potting soil, feeding on fungi, decaying organic matter, and sometimes plant roots. The single most effective step is to let the top layer of soil dry out completely between waterings. Fungus gnats thrive in consistently damp conditions, so overwatering is the primary reason they show up. Make sure your pots have good drainage and aren’t sitting in saucers of standing water.
If drying out the soil isn’t enough, you can drench the soil with a product containing Bti, a naturally occurring bacterium that kills fly larvae but is harmless to plants, pets, and people. Products like Mosquito Bits are widely available at garden centers. Bti doesn’t persist in indoor soil, so you may need to reapply every five days or so until the population is gone. Another option is beneficial nematodes (specifically the species Steinernema feltiae), which you mix with water and pour into the soil. These nematodes actively hunt larvae and can provide longer-lasting control because they reproduce in moist soil, especially when temperatures are between 60° and 90°F.
Phorid Flies
Phorid flies are frequently mistaken for fruit flies because they’re roughly the same size, about an eighth of an inch. But two traits set them apart. First, they lack the red eyes that fruit flies are known for. Second, and more telling, phorid flies prefer to run. They scuttle erratically across countertops and walls rather than flying, which is why they’re nicknamed “scuttle flies.” Viewed from the side, they have a noticeable hump on the back between the head and abdomen, and their hind legs are flattened and disproportionately large.
Phorid flies breed in decaying organic material, similar to drain flies, and sometimes in the same microbial films that coat drain interiors. But they can also breed in broken garbage disposals, under cracked floor tiles where moisture collects, and in any hidden pocket of rotting matter. If you’re seeing small flies that don’t have red eyes and seem to run more than fly, check drains, garbage disposals, and any areas where moisture and organic debris might accumulate out of sight.
Blow Flies
Blow flies are hard to miss. They’re about the size of a house fly or slightly larger, and they have a striking metallic sheen, usually bright green, blue, or a coppery mix. If you suddenly find several of these buzzing around a room, it usually means something has died nearby. Blow flies and their close relatives, flesh flies, invade homes specifically to lay eggs on decaying animal carcasses. A dead mouse in a wall void, a bird in an attic, or even a forgotten piece of raw meat can attract them.
The fix is straightforward but sometimes unpleasant: find and remove the carcass. Once the food source is gone, the adults will die off or leave within a few days. If you can’t locate the source, the flies will eventually stop once the carcass dries out completely, though this can take a week or two.
Less Common Indoor Flies
A few other species show up often enough to be worth knowing about. The little house fly is roughly two-thirds the size of a common house fly and lacks the four dark back stripes. It holds its wings flat over its body at rest, rather than in a V-shape like the house fly. These tend to circle aimlessly in the middle of a room, often under light fixtures.
Stable flies look similar to house flies but have a visible, needle-like mouthpart sticking forward from the head, and they bite. They breed in wet straw, grass clippings, and decaying vegetation rather than garbage, so they’re more common near farms or yards with piled lawn waste. Cluster flies, which are slightly larger and more sluggish than house flies, enter homes in fall to overwinter in wall voids and attics. You’ll often see them buzzing slowly at windows on warm winter days.
Quick Identification Guide
- Tiny with red eyes, near fruit or kitchen: Fruit fly
- Tiny, runs across surfaces, humped back: Phorid fly
- Tiny, long antennae, near houseplant soil: Fungus gnat
- Small, fuzzy, moth-like, near drains: Drain fly
- Medium, gray, four dark stripes on back: House fly
- Medium, metallic green or blue: Blow fly
- Medium, needle-like mouthpart, bites: Stable fly
In every case, the most reliable long-term solution is the same: find and eliminate the breeding source. Traps and sprays reduce adult numbers temporarily, but new adults will keep emerging as long as larvae have somewhere to develop. Once you identify the type of fly, you know exactly where to look.