Order: Diptera
Common Name--Flies and Mosquitoes

The order Diptera is pronounced "DIP-ter-a." The name Diptera is taken from the Greek words: "di," which means two, and "ptera," which means wings. This name refers to the fact that flies have only two wings, although there are some that are wingless. Diptera and Coleoptera are the oldest names of orders still in use. These names were first used by Aristotle more than 2300 years ago.

There are common names for many kinds of flies, including mosquitoes, midges, gnats, bots, keds, crane flies, horse flies, flat-footed flies, and fruit flies. Some common names refer to entire families of flies, and other names, such as house fly, refer to a single species. In Diptera, the word "fly" is always written separately from the rest of the common name. Many insects in other orders also are called flies, such as dragonflies and sawflies, but their common name is always written as one word.


There are about 120,000 named species of flies in the world. Some researchers estimate that more than a million species have yet to be described and named.

More than 19,500 species in 121 families are found in the United States and Canada. About 1,800 of these species, or 10% of the total, are crane flies in the family Tipulidae. Other families with more than 1,000 species each include Chironomidae (midges), Cecidomyiidae (gall midges), Tachinidae (tachinids), Asilidae (robber flies), and Dolichopodidae (long-legged flies).


Adult flies are often found on flowers, sap, feces, garbage, and animals, both dead and alive. Aquatic larvae can be found in streams, ponds, water in holes of tree trunks, and any other place where water accumulates. Larvae of filter flies (family Psychodidae) live in drains of sinks and sewers. The larvae of certain flies in the family Ephydridae breed in the Great Salt Lake in Utah. Another species of Ephydridae, Helaeomyia petrolei, has larvae that live in pools of crude oil. Other fly larvae live in the soil, under bark, in decaying materials, in fungi, and in plants. Some flies are known to live in nests of ants and termites.

Form and Function

Adult flies range in length from 0.04 to 1.6 inches, although rarely they may be more than two inches long. Most flies have very large eyes, and some of these eyes have thousands of lenses. Eyes of some horseflies (family Tabanidae) have beautiful color patterns. Stalk-eyed flies have eyes at the ends of long projections from the head.

Most flies are black, gray, or brown, but others have brighter colors of yellow, orange, blue, and green colors. Some flies, especially flower flies (family Syrphidae), have colors and forms that mimic bees and wasps. Flies are often covered with spines, setae (hairs), and occasionally scales. The setae are arranged in distinct patterns which can help in distinguishing different flies from one another.

Most flies have a pair of wings on their mesothorax. The wings can be transparent, or they can have different patterns. The veins in the wing often are used to identify the different families of flies. Flies also have a pair of knob-like structures called halteres on their metathoraxes. The halteres are actually hind wings that serve to stabilize flight, or to help the fly stay on an even course of flight.

Most flies have sucking mouthparts that are modified in different ways. Some flies, such as mosquitoes, have piercing mouth parts. Other flies, such as the house fly, have sponging mouthparts. Some flies do not have functional mouthparts and do not feed as adults.

Many flies, such as mosquitoes, have a long antenna. This long antenna may be thread-like or be feathery. The antennae in many flies are short and three-segmented with a long hair, termed arista, arising from the third segment. This arista may be a simple bare hair, or it may be feathery.

Larvae of flies are grublike and do not have legs. Larvae of some flies, such as mosquitoes, have large heads and chewing mouthparts. Larvae of many flies do not have a distinct head or chewing mouthparts, and these are called maggots.

Pupae of mosquitoes are called "tumblers" because of their tumbling motion from the surface of the water when disturbed. Many flies have a pupa enclosed in a puparium. The puparium is the dried skin of the maggot that surrounds the pupa, similar to the way a cocoon surrounds a moth pupa.

Life Cycle

Flies have complete metamorphosis with egg, larva, pupa, and adult. Eggs are usually deposited on or near the larval food. In some flies, such as those in the family Tachinidae, the eggs hatch inside the female and the young larvae are deposited by the fly. In a few flies, including the African tsetse fly, the female nurses the larvae with glands inside her reproductive tract until the larvae mature. The mature larva comes out of the female and quickly pupates.

Some species of gall midges (family Cecidomyiidae) give birth to young without ever mating, which is known as parthenogenesis. The bizarre thing about these gall midges is that the larvae develop inside a mother larva, eventually consuming and killing her. These larvae become mothers to be consumed by their own larvae. This process continues for several generations until the larvae do not bear young and pupate to form adult flies.

Mosquitoes eggs will not hatch unless they are in water. The water may be in a lake, puddle, bucket or other container, a knot hole in a tree trunk, or other such place. The female of a species in the genus Amigeres will lay its eggs on its hind leg, and then stick its leg into water for the eggs fall off. In the cold Arctic regions, mosquitoes may be in the egg stage for more than 11 months, hatching only after the snow melts. The larval and pupal stages last only a couple of weeks, and the adult emerges to lay eggs that will hatch in another 11 months.

Larvae go through 3-9 stages (instars) before entering the pupal stage. At the end of the pupal stage the adult fly emerges and mates. Males of mosquitoes and midges swarm in large numbers to mate. The humming of thousands of male wings makes a sound that attracts the females. Males of other flies have courtship dances, waving their patterned or spotted wings to gain the attention of the female. Males of some balloon flies (family Empididae) present the female with a gift before mating. This gift is usually a small prey insect that is wrapped in silk, resembling a small balloon.

Form and Feeding Habits

Diptera has more diversity in feeding habits than any other order of insects. Various species are predators, parasites, plant feeders, and scavengers of animal droppings and dead plants and animals. Adult flies feed on liquid food, but larvae of various species can feed on liquid or solid food. Some species live most of their lives on or inside vertebrate animals as parasites, and other species visit the animals to feed on secretions from the eyes or noses. Mosquitoes and many other biting flies have females that feed on the blood of vertebrates, and some biting midges feed on the blood of insects.

Many adults and larvae feed on plants, algae, and fungi. Some adults feed on pollen or nectar, and many feed on tree sap. Many species have larvae that bore in stems and roots of plants. Species in the family Agromyzidae have larvae that are leaf miners. Larvae of fruit flies (family Tephritidae) are serious pests of fresh fruit and vegetables. Overripe or decaying fruit can be infested by larvae of small fruit flies (family Drosophilidae). However, these flies actually are feeding on yeast in the decaying fruit rather than the fruit itself.

Species in the family Cecidomyiidae are known as gall midges. These midges form distinctive galls on different plants. A gall with an eye-shaped pattern is found on maple leaves. A single leaf of the hickory tree may have four or more different shapes of galls, each a different species, on the same leaf. Depending on the species, a gall might include a single or several larvae. Other gall forming Diptera include some species in the family Tephritidae.

Some flies parasitize other insects and arthropods. Big-headed flies (Pipunculidae) are parasites of Homoptera (leafhoppers and planthoppers especially), and thick-headed flies (Conopidae) are parasites of bees and wasps. Some species of flesh flies (Sarcophagidae) parasitize spiders. All the species in Tachinidae, the second largest family in North America, parasitize other insects, especially caterpillars, sawflies, and beetles.

Many Diptera are predators on insects and other invertebrates. Larvae of marsh flies (family Sciomyzidae) feed on snails and slugs. Adults of long-legged flies, (family Dolichopodidae), robber flies (family Asilidae), and many dance flies (family Empididae) are predaceous on other insects as adults.

Adults of some flies are external parasites of birds and mammals and feed on the blood of the host. Although these flies live most of their lives on the bird or mammal, they do not kill the host as do the parasites of insects. Bat flies, which may have winged or wingless adults, are external parasites of bats. Louse flies include external parasites of birds, but one wingless species is a parasite of sheep. Larvae of these flies develop within the reproductive tract of the adult female, and they change quickly into pupae after being deposited by the mother.

Internal parasites include larvae of bot flies and warble flies (family Oestridae), which attack mammals. Warble flies attack cattle, and the mature larva causes a bump (or warble) on the back of the animal. Bot flies are parasites of horses, rabbits, squirrels, mice, and other animals. The human bot fly, Dermatobia hominus , occurs in Central and South America where it usually is a parasite of cattle and other animals. Some blow flies (family Calliphoridae) and flesh flies (family Sarcophagidae) also may feed on living tissue of animals.

Natural Enemies

Predators of Diptera include amphibians, reptiles, fishes, birds, insects, spiders, and other arthropods. Flies that feed on dead animals have competition from carrion beetles (family Silphidae) for the same food. The beetles carry small mites (class Arachnida) that prey on the eggs of flies that come to the dead animal. Some rove beetles wave the tips of their abdomens in a circular motion to attract the attention of flies. A fly that comes too close to the beetle is grabbed by the beetle's long mandibles.

Flies are also attacked by viruses, fungi, bacteria, and other microorganisms. Dead flies often can be found inside a house on a window pane. A close examination of this dead fly will show that it is surrounded by a round ring of spores from the fungus that killed it.

Certain carnivorous plants can also be enemies of flies (and other insects). Pitcher plants, sundews, and Venus fly traps are some examples of plants that obtain some of their nutrients from trapped insects.

Olympic Feats and Other Strange Facts

It would take approximately 1,200,000 mosquito bites to totally drain the blood from an adult human.

Yellow fever is caused by a virus that is transmitted by the mosquito Aedes aegypti. It was one of the worse diseases in the United States before the 20th century. The first capital of the United States was in Philadelphia, Pennsylvania. The capital was moved to New York City and later to Washington, D.C., because of the large numbers of Aedes aegypti mosquitoes and cases of yellow fever in Philadelphia.

Some bot flies, such as the human bot fly, do not lay their eggs on their animal host. Rather, the female bot fly lays the egg on a biting fly, such as a mosquito, and this biting fly carries the egg to its animal host. When the mosquito bites the animal, the egg of the bot fly hatches, and the larva burrows into the animal's skin.

House flies beat their wings at a rate of 330 beats per second. Mosquitoes beat their wings at a rate of 600 beats per second. Some midges beat their wings at a rate of 1,040 beats per second. By contrast, a hummingbird beats about 75 times a second, and the fastest that humans can contract their muscles repeatedly is about 10 times per second.

The larvae and adults of Scatella thermarum live in hot springs in Iceland. The adults live on mats of algae that float on the surface of the hot springs, but the larvae actually live in the water that reaches temperatures of 118 degrees Fahrenheit (48° degrees Centigrade).

The larvae of some fungus gnats (family Mycetophilidae) can spin webs of silk with their mouthparts. One silk spinning species, Arachnocampa luminosa, lives in a cave called the "Glow Worm Cave" in Waitomo, New Zealand. The larvae of this species are luminescent, making light similar to that of firefly beetles. The larvae use their glow to attract midges that live in the cave. The midges become trapped in the sticky strands of silk and are eaten by the fungus gnat larvae.

The larvae of some species of fungus gnats in the genus Sciara sometimes travel together across the ground in a close file. They travel so close together that they resemble a large worm or snake many feet long.

The dehydrated larvae of an African species of Chironomidae, Polypedilum vanderplanki, can withstand exposure to liquid helium (at a temperature of -270° Centigrade) for up to five minutes with a 100% survival rate.

Larvae of some Chironomidae can live in mud and water with low levels of oxygen. They have red blood, similar to mammals, which is better for carrying oxygen through their bodies.

The chironomid midge, Charoborus edulis, has swarms of millions of individuals near lakes in Africa. Natives in these areas collect the midges and press the bodies together forming a type of bread called Kunga cake that is eaten.

Black fly larvae live under rocks and other objects in fast flowing streams. The larva spins a safety line of silk and attaches it to their home in the water. If they get washed away by the water's current, they can climb up their silken rope to get back to their home.

The larva of a soldier fly, Potamida ephippium (family Stratiomyidae), is a scavenger in the ant nests of Formica fuliginosa. The larva lives up to four years in these nests, which is a very long life time for a Diptera larva.

The phorid fly, Conicera tibialis , can live for more than a year and have several generations inside coffins. These flies feed on the dead bodies and are called coffin flies.

In Greek mythology, there was a woman named Musca who was a beautiful and talented singer. She was, unfortunately, the rival of the goddess Diana for the love of a fellow named Endymion. Diana did not want a rival, so she turned Musca into a fly. The genus of the house fly, Musca, was named after the woman who was turned into the fly.

The Good and The Bad

The presence of a single buzzing fly can be a nuisance to many people, and swarms of flies can be a plague, especially if they are biting flies. Many flies are serious pests of crops, farm animals, and humans. Flies cause more illnesses to and deaths of humans than any other group of insects. Fruit flies, such as the medfly, are major pests of fruits and vegetables. The Hessian fly, which feeds on wheat, and the seed corn maggot cause great losses of grain crops.

The "love-bug" in southern United States, which is a fly named Plecia nearctica (family Bibionidae), is a pest of the automobile. These flies live as larvae in decaying vegetation, and adults emerge in large numbers to mate. The mating flies damage the paint and clog the radiators of cars, causing them to overheat. At the same time, the cars’ windshields become so splattered with the flies that driving can become hazardous.

Mosquitoes transmit pathogens that cause malaria, yellow fever, dengue fever, encephalitis, and other diseases. In addition to human diseases, dog heartworm is transmitted by mosquitoes. Malaria, which is transmitted by species in the genus Anopheles, is the worst of these diseases. The World Health Organization estimates that more than 500 million people are infected with malaria each year. Of these, more than 2 million people die each year, primarily children living in Africa.

Many disease pathogens are transmitted by flies in areas of the world outside the United States. The tsetse fly of Africa transmits a pathogen causing African sleeping sickness. Black flies (family Simuliidae) and sand flies (family Psychodidae) also are involved in the transmission of serious diseases of humans.

House flies are major transmitters of pathogens that cause dysentery, typhoid fever, and other diseases. Researchers have estimated an average house fly in a residential area carries 1,941,000 bacteria, mostly on their mouthparts and the pads of their feet. A single fly on a person's food can leave more bacteria than hundreds (if not thousands) of cockroaches.

On the good side, many flies are quite beneficial. Parasitic and predatory flies aid in the population control of many pest insects. Many flies also play an important role in recycling dead plant and animal matter. Flies are the second most important group of flower pollinators after bees and wasps. Much of our knowledge about genetics is based on research that has been done with small fruit flies (family Drosophilidae). Flies provide food for many animals, and midge larvae are a major part of the diets of many fish.

Selected Families of North American Diptera

Tipulidae (crane flies)

Bibionidae (march flies)

Mycetophilidae (fungus gnats)

Cecidomyiidae (gall midges)

Psychodidae (moth flies and sand flies)

Culicidae (mosquitoes)

Simuliidae (black flies)

Ceratopogonidae (biting midges, punkies, no-see-ums)

Chironomidae (midges)

Tabanidae (horse and deer flies)

Stratiomyidae (soldier flies)

Mydidae (mydas flies)

Asilidae (robber flies)

Bombyliidae (bee flies)

Empididae (dance flies)

Dolichopodidae (long-legged flies)

Phoridae (humpbacked flies)

Syrphidae (flower flies)

Tephritidae (fruit flies)

Agromyzidae (leaf miner flies)

Sciomyzidae (marsh flies)

Drosophilidae (pomace flies, vinegar flies, small fruit flies)

Ephydridae (shore flies)

Chloropidae (grass flies)

Anthomyiidae (anthomyiid flies, root maggots)

Muscidae (muscid flies, house flies, face flies, stable flies, tsetse flies)

Calliphoridae (Blow flies)

Sarcophagidae (flesh flies)

Oestridae (warble and bot flies)

Tachinidae (tachinid flies)

Hippoboscidae (louse flies)

Streblidae (bat flies) .

A complete list of Diptera families and additional photographs are available at the USDA Systematic Entomology Laboratory Web site on Diptera Flies! Flies! Flies!.

Selected References

Arnett, Ross H. Jr. American Insects, A Handbook of the Insects of America North of Mexico. New York: Van Nostrand Reinhold Co., 1985.

Borror, Donald J. and White, Richard E. A Field Guide to the Insects of America North of Mexico. Boston: Houghton Mifflin Co., 1970.

Borror, D.J., Triplehorn, C.A., and Johnson, N. F.. An Introduction to the Study of Insects. Saunders College Publishing, 1989.

Dethier, Vincent G. To Know a Fly. Oakland, California: Holden-Day, Inc., 1962.

Oldroyd, Harold. Natural History of Flies. World Naturalists Series. Norton Publishing, 1964.


For an extensive list of Diptera Web sites, go to the Links Component of the module.

Picture Credits

Dr. Ross E. Hutchins (Deceased)
Mississippi Entomological Museum

A crane fly

Mosquito larvae getting air with siphons

Goldenrod gall fly

Maggot of house fly

Pupa of mosquito in water

Tachinid parasite emerging from puparium

A nectar feeding male mosquito

Gall of Cecidomyiidae on maple

Predaceous robber fly

The house fly, Musca domestica

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