True Flies

The muscid flies (family Muscidae) include more than 700 species in North America, including some important pests. The house fly (Musca domestica) is one of the most familiar flies to most people, because it breeds readily in garbage and other organic debris, and can be very abundant in dirty places around homes, villages, and cities. The house fly does not bite, but it can be a vector of some diseases of humans, spreading the pathogens by contact, for example, by walking on food that is later eaten by people. The face fly (Musca autumnalis) tends to cluster around the face of cows, where it feeds on mucous secretions around the nostrils and eyes, causing great irritation to the livestock. The stable fly (Stomoxys calcitrans) and horn fly (Haematobia irritans) are biting flies that greatly irritate livestock. Species of tsetse flies (Glossina spp.) occur in Africa, and are the vectors of sleeping sickness and related diseases of people, livestock, and wild large mammals.

Blow flies (family Calliphoridae) are scavengers, whose larvae feed on dead animals, excrement, and similar, rotting debris. Although a carcass teeming with writhing maggots is a rather disgusting spectacle, it must be remembered that blow flies provide a very useful ecological service by helping to safely dispose of unsanitary animal carcasses. A few species of blowflies lay their eggs in wounds on living animals, and the larvae may then attack living tissues, causing considerable damage. The screw-worm (Cochliomyia hominivorax) is an important pest in this regard, causing severe damages to cattle populations in some areas.

Flower flies or syrphids (family Syrphidae) include about 1,000 species in North America. Adult syrphids can be quite common in some habitats, where they are typically seen hovering in the vicinity of flowers. Many species of syrphids are brightly colored, sometimes with a black and yellow banding that is an obvious mimicry of bees and wasps.

The fruit fly family (Tephritidae) is made up of several hundred North American species, some of which are important pests in agriculture. The apple maggot (Rhagoletis pomonella) burrows in the fruits of apples and other fruits, while the Mediterranean fruit fly or medfly (Ceratitis capitata) is a serious pest of citrus fruits.

The small fruit flies (family Drosophilidae) are common in the vicinity of decaying vegetation and fruit. The species Drosophila melanogaster has been commonly used in biological laboratories for studies of genetics, because it is easily and quickly bred, and has giant chromosomes that can be readily studied using a microscope.

The warble and bot flies (family Oestridae) are large, stout, fast-flying flies that have a superficial resemblance to bees. The larvae of these flies are parasitic on large mammals, living in the flesh just beneath the skin. Some species are serious pests of agricultural animals, for example, the sheep bot fly (Oestrus ovis) and the ox warble fly (Hypoderma bovis). Warble flies are extremely irritating to cattle and to wild ungulates—there are reports of caribou being driven to distraction by warble flies, and jumping off cliffs in desperate attempts to escape these nasty pests.

Tachinid flies (family Tachinidae) include more than 1300 species in North America. The larvae of tachinids are parasitic on other species of insects, including some economically important pests, which are essentially eaten alive by the tachinid. As such, some species of tachinids provide a useful service to humans.

The robber flies (family Asilidae) are a diverse group, with more than 800 species in North America. Robber flies are predators of other insects, which are captured in flight.

Seaweed or wrack flies (family Coelopidae) are dark-colored flies that can be very abundant along marine shores, where they breed in natural piles of seaweed compost, with the adults swarming abundantly above, often attracting large numbers of shorebirds and swallows.