Main Categories of Flies
The vast majority of flies are either filth flies or biting flies. There are other common categories of fly, but they’re not typically what people are talking about when they use the word “fly” colloquially. Generally speaking, the two major categories are: Filth flies: Any fly that breeds in garbage, feces, or some other traditionally dirty environment is going to be a filth fly. Filth flies spread disease, which is why they’re generally an issue for humans. Biting flies: Any fly that bites is going to generally qualify as a biting fly. While most biting flies feed on livestock, many of them will bite people. They can also spread disease while exposing you to potentially painful bites.
Most Common Types of Flies
House flies House flies are one of the most common types of fly in a lot of the world, and they’re what most people probably imagine when they hear the word “fly.” Appearance: ⅛-¼ in (3.18 mm-6.35 mm) in length, house flies have 4 dark stripes on top of their thorax. Behavior: House flies tend to move erratically, only landing to clean their mouth, lay eggs, or eat. Category: Filth fly Danger level: House flies are thought to help spread around 65 different diseases that are dangerous to people, but they’re not uniquely problematic.
Little house flies Also known as the lesser house fly, the little house fly is nearly identical to a traditional house fly in behavior and appearance. The only difference is that their life cycles are much shorter and they tend to be more attracted to farms and livestock. Appearance: They’re about ⅔ the size of the house fly’s body, which usually makes them 4-7 mm in length. Behavior: Little house flies also move in an erratic pattern, and they tend to hover in people’s faces. They also flock to animals where you can see them swarming in semi-circles. Category: Filth fly Danger level: Little house flies likely carry more diseases than their larger brethren, notably diseases that cause food poisoning and dysentery.
Fruit flies Also known as vinegar flies, fruit flies are a common pest that swarm and spread rapidly. They’re much more common in the summer and spring when the days are warmer. Appearance: Less than ⅛ in (3.18 mm) in length, fruit flies typically just appear as flying black dots. If you look closely though, they’re light brown with bright red eyes. Behavior: Fruit flies aren’t very adventurous and they tend to congregate wherever their primary food source is. They usually fly in small loops and tend to leisurely hang out on their food. Category: Filth fly Danger level: Fruit flies carry a lot of dangerous diseases, and they proliferate very quickly. A single female fruit fly can lay up to 900 eggs, so they become more dangerous the longer you ignore them.
Bluebottle flies Also known as blow flies, bluebottle flies are notable for their metallic blue appearance. They’re scavengers that primarily eat animal decay, although they can’t bite people, so there’s nothing to worry about there at least. Appearance: Bluebottles are around ⁄2 in (1.3 cm) long and have a bright, blue sheen. There is a greenbottle variant that is identical except it’s green instead of blue. Behavior: Bluebottles are comically loud when they fly (these are the flies that make “bzzzz” noises), and their unpredictable flight typically leads them to whatever the nearest dead thing is. Category: Filth fly Danger level: They can certainly spread disease (notably E. coli), but given their normal lack of interest in people, they’re one of the less nefarious flies out there.
Cluster flies Cluster flies are pretty hardcore. When they’re born, they immediately begin to burrow underground where they look for an earthworm to eat. They’re dormant when it’s winter, which is when you often see cluster flies indoors. Appearance: They look pretty indistinguishable from regular house flies, although they’re missing the stripes on the thorax. Behavior: Cluster flies are slower than a lot of other flies, and they can behave kind of annoyingly by flying at you and then bouncing off to go elsewhere. Category: Cluster flies are a rare kind of fly known as a grass fly. Grass flies are defined by their eating of (or breeding in) grass. Danger level: They’re extremely annoying, but luckily, cluster flies aren’t a big threat to people. They can be bad for some crops, though.
Drain flies Also known as sewage flies or bathroom flies, drain flies grow wherever you find darkness and moisture alongside dead organic material. Unfortunately, that makes sewer lines and drains the ideal breeding ground. These flies also appear in clogged gutters, overwatered potted plants, and compost areas. Appearance: These hairy little flies have wide wings that almost give them a moth-like appearance. Behavior: These flies really just hang out around standing water or dead organic material. You might see these flies just resting on walls or surfaces. Category: Filth fly Danger level: Surprisingly, sewer flies don’t actually pose a serious risk to humans despite their usually nasty origins. They may damage common household plants, though.
Fungus gnats Fungus gnats are small flies that tend to feed on the organic matter in soil. As a result, you’ll often find them in homes with a lot of plants. Appearance: Fungus gnats are tiny, delicate, and rarely more than ⁄16 in (0.16 cm) in length. They kind of resemble tiny mosquitoes. Behavior: Fungus gnats are pretty weak fliers, so they tend to do a lot of crawling and skittering. They’re attracted to light, so you’ll often find large numbers of these flies hanging out near windows. Category: Filth fly Danger level: These flies are annoying, but they don’t pose any risk to people. They can irritate plants, though.
Picture-winged flies Picture-winged flies are a lot like fruit flies in behavior and feeding habits. They tend to congregate anywhere you’ll find moisture and decay. Appearance: Picture-winged flies are notable for the distinct banded patterns that appear on their wings. Depending on the subspecies (there are 130 different picture-winged flies), they range from ⁄4–⁄2 in (0.64–1.27 cm) in length. Behavior: These goofy fliers don’t tend to be very graceful. They fly kind of erratically and often bounce around their food. Category: Filth fly Danger level: None. In fact, picture-winged flies are pretty important for the environment. They help the compost process along, and the fact that they carry no diseases is just icing on top.
Flesh flies Flesh flies lay eggs in decaying flesh, which is where they get their name. They’re pretty exclusively interested in eating, so you don’t tend to see flesh flies anywhere where there isn’t food. In fact, if you find a lot of them in your home, it’s a big sign an animal has died inside your walls. Appearance: They’re a little bigger than standard house flies and can get almost 1 in (2.5 cm) in length. They look a lot like house flies, actually, although they have a checkerboard pattern on their abdomen in addition to the stripes on their thorax. Behavior: These flies aren’t especially agile. They really only care about eating dead things, so you don’t see them doing much else beyond eating and looking for food. Category: Filth fly Danger level: Flesh flies can spread disease, so it’s important to keep them out of your living area whenever possible. Luckily, flesh flies tend to avoid humans since people rarely leave decaying flesh around.
Phorid flies Also known as scuttle flies, hump-backed flies, and coffin flies, these tiny flies are found anywhere you’d find moisture and decaying organic matter. In fact, the nickname “coffin fly” refers to the fact that you often find these tiny flies in great numbers when you explore mausoleums or when you excavate corpses. Appearance: These flies are very tiny, coming in at ⁄64–⁄4 in (0.40–6.35 mm) long. They’re usually tan, black, or a combination of the two colors. If you look very closely, phorid flies are distinct for having a hump on their thorax and spiky hairs on their face. Behavior: Phorid flies don’t like to fly, oddly enough. Instead, they prefer to run across surfaces. When they do fly, they’re pretty inelegant. Category: Filth fly Danger level: Normally, very low. However, phorid flies have been found to lay eggs in the eyes, nose, or throat of people when they sleep. They also lay eggs in food or open wounds and in food, which can make people sick. These cases are rare, though.
False stable flies False stable flies are a lot like standard house flies. They’re mainly interested in eating decaying organic matter, which also happens to be where they lay their eggs. Appearance: These flies can get up to ⁄4 in (1.9 cm) in length. They’re usually dark gray but otherwise look like basic house flies. Behavior: False stable flies tend to fly very slowly in larger loops than other kinds of flies. They’re relatively active, and if they aren’t feeding, they’re usually buzzing around looking for food. Category: Filth fly Danger level: These flies aren’t dangerous for people. They don’t tend to spread disease and they don’t bite.
Stable flies Stable flies and false stable flies are nearly identical in appearance, but they’re otherwise very different. They tend to eat livestock, ergo the name “stable fly.” Appearance: Stable flies are slightly smaller than false stable flies, but almost identical in appearance otherwise. They also have a bayonet-like mouthpiece that allows them to stab things. Behavior: Stable flies fly very fast and with great conviction. They tend to hang out on or near their primary food source, so if you see flies following a farm animal around, they’re probably stable flies. Category: Biting fly Danger level: Stable flies have a very painful bite. They also spread diseases that impact both livestock and people (including anthrax). Luckily, stable flies much prefer livestock to people.
Horse flies Horse flies are actually super cool. They have thermal vision that allows them to see heat (like the Predator!) and they’re able to track large objects over an extended period of time. Horse flies also react to movement (like the T. Rex in Jurassic Park!). Appearance: These flies can get up to 1 ⁄4 in (3.2 cm) in length, and they have large eyes that really give them a freaky appearance. Outside of the black horse fly, the eyes are also notable for being brightly colored and vivid. Behavior: Horse flies are aggressive. They’ll fly at you and pursue you until they tire out or find some other target. They also tend to attack cars, which they mistake as horses with some frequency. Category: Biting fly Danger level: Their bite is extremely painful, but they aren’t actually dangerous to people unless they happen to be allergic to horse flies.
Deer flies If horse flies are known for attacking and feeding on horses, deer flies are known for attacking and feed on…you guessed it, people! And cows! The deer fly is very similar to the horse fly except they differ in appearance and prey selection. Appearance: Deer flies can be up to 1 ⁄4 in (3.2 cm) in length and have the same bug-eyed peepers that horse flies have. However, they have a notable gold and black banding color that makes them look more like wasps than flies. Behavior: Deer flies tend to be active both during the day and at night. Like horse flies, they pursue their targets when they sense movement. Category: Biting fly Danger level: Deer flies tend to be more aggressive towards humans, but their bite is luckily just a bite. They aren’t known for being serious vectors for disease.
Biting midges Popularly known as “no-see-ums,” biting midges are incredibly tiny flies that a lot of people can’t even see with their naked eye. Appearance: Biting midges are so small that it’s hard to make out their features. They’re less than 3 mm long in most cases—just big enough to register as a fluttering black dot. Behavior: These midges are generally weak fliers, so they’re rarely flying very high. They tend to swarm around whatever they’re trying to eat. Category: Biting fly Danger level: Biting midges are usually a pretty mundane pest, but they are a unique vector for Oropouche, a virus that can cause fevers and body aches. Normally, Oropouche isn’t life-threatening, but it can trigger meningitis or encephalitis, which are life-threatening.
Black flies Also known as buffalo gnats or turkey gnats, black flies are annoying biting flies that tend to be especially annoying in the summer. They’re unique because they lay their eggs in flowing water, which makes preventing infestations a unique challenge. Appearance: Black flies are varying shades of black and dark brown. They’re rarely bigger than 5-15 mm in length, but they have an easy-to-spot arch in their body that makes them stand out. Behavior: They’re most active during daylight where you can find them hovering a few feet off the ground and flying in a zigzag pattern. Category: Biting fly Danger level: Pretty low. It’s possible for biting flies to spread disease, but there aren’t a ton of documented examples of this happening. They’re mainly just annoying.
Sand flies Sand flies are a lot like horse flies, except they’re primarily found in more arid, sandy areas and they’re tiny. They also work in groups, which is very unique for biting flies. Notably, their bites are often confused with mosquito bites because they cause itchy bumps to appear days after their bites. Appearance: They’re rarely more than 1-4 mm in length, but you can usually spot them because they attack and fly in swarms. At a glance, they’re pretty hard to distinguish from gnats and biting midges. Behavior: Sand flies are found in tropical and arid areas. You’ll see them flying in swarms and congregating in light. Category: Biting fly Danger level: Sand flies are dangerous to people and pets. They spread a variety of dangerous diseases, including Leishmaniasis—a parasitic infection that can cause organ damage and ulcers.
Mosquitoes Yup, mosquitoes are a type of fly! Believe it or not, there are actually 3,500 different subspecies of mosquitoes. They’re one of the most studied flies on the planet because they’re a major vector for disease transmission, their bite is extremely irritating, and they’re about as annoying as a creature can possibly be. Appearance: Typically around ¼-1/2 in (6.35-12.7mm) long, mosquitoes are instantly recognizable with their rounded thorax, wiry limbs, and long beak-like mouth that they use to suck blood. Behavior: Mosquitoes congregate around water, which is where they hatch and lay eggs. They spend their time looking for animals and fruits to feed on. Category: Biting fly Danger level: High, relatively speaking. While most people in wealthier countries don’t have much to worry about, mosquitoes can spread malaria, dengue fever, Zika virus, yellow fever, or West Nile virus. This actually makes them the deadliest creature in the world.
Getting Rid of Flies
Remove the source of the fly infestation to get rid of them. Generally speaking, flies do not live very long. If you get rid of the food source they need to breed, you’ll get rid of the flies in no time. Lews explains that removing the source of the problem will keep the flies from continuing to breed and bother you. For filth flies: Get rid of any excess trash, clean up pet waste, and maintain a clean environment. Set up fly traps in the meantime to catch any adults. For drain flies, pour some bleach down your drains. For fruit flies, the old vinegar cup trick works. Fill a small cup with vinegar, pull plastic wrap over the top, and poke holes in the plastic wrap. For biting flies: Remove the food source. If flies are bothering your livestock, you may need to treat the problem directly with traps and animal fly spray (seriously, it’s a real thing and it works). Keep pools and outdoor water sources covered (and treated, if possible).
Expert Advice on Prevention
Put screens on all of your doors and windows. Paragon Pest Control says that if you don’t want to buy a screen door, buy those door-length screens with magnets that snap together. They even suggest adding screens to your garage door if you keep your trash in the garage. If you don’t want to hire a contractor to install full-sized screens in your window frames, you can buy an adjustable screen to put in the window whenever you open it.
Keep your pets inside whenever possible. Paragon Pest Control explains, “The basic way to prevent pests is to keep pets inside.” When it comes to prevention, there are anti-fly products and fly repellents you can buy to keep flies from biting up your dog or cat. They say, “There are some newer products on the market that people use that are safe to put on the animals.” Check out your local pet store or talk to a vet for their recommendations. Give your cats and dogs a monthly preventative heartworm and flea treatment to prevent the two most common insect issues.
Locate the breeding ground if flies keep coming back. Lewis points out, “Instead of focusing on the flies in the kitchen or wherever, focus your attention on locating the source where the flies are breeding. Flies will breed in pet droppings, decomposing trash, and in rodent carcasses. If you can find and remove the source(s) the flies are breeding in, you can quickly achieve total fly control and potentially never see a fly in your kitchen again.” Take out the trash regularly to avoid giving flies the food they might need to flourish. Get rid of all standing water before flies have time to breed. Avoid overwatering plants or leaving plant cuttings in unmonitored water for too long. Don’t let yard waste compost in the open air anywhere near your home.
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