Flies, gnats, maggots, midges, mosquitoes, keds, bots, etc. are all common names for members of the order Diptera. This diversity of names documents the importance of the group to man and reflects the range of organisms in the order. The order is one of the four largest groups of living organisms. There are more known flies than vertebrates. These insects are a major component of virtually all non-marine ecosystems. Only the cold arctic and antarctic ice caps are without flies. The economic importance of the group is immense. One need only consider the ability of flies to transmit diseases. Mosquitoes and black flies are responsible for more human suffering and death than any other group of organisms except for the transmitted pathogens and man! Flies also destroy our food, especially grains and fruits. On the positive side of the ledger, outside their obviously essential roles in maintaining our ecosystem, flies are of little direct benefit to man. Some are important as experimental animals (Drosophila) and biological control agents of weeds and other insects. Others are crucial in helping to solve crimes (for an example click here).
Some 150,000 different kinds of flies (Order Diptera, Class Insecta, Phylum Arthropoda) are now known and estimates are that there may be more than 1,000,000 species living today. These species are classified into 188 families (see list of recognized families) and some 10,000 genera. Of these, some 3,125 species are known only from fossils, the oldest of which, a limoniid crane fly, is some 225 MILLION years old (Upper Triassic (Carnian)). (See the Databases of World Diptera for the names of flies and information on those names and groups of flies.)
A basic introduction to flies is provided by Harold Oldroyd's Natural History of Flies (1964, The World Naturalist series, Norton). A more technical overview and general classification with key to the basic groups (genera) found in North America is provided by the Manual of Nearctic Diptera (3 vols., 1981, 1987 & 1989, Agriculture Canada). Also see the FLYTREE project for information on the classification of flies. If you want to know more about the morphology of flies or need to know the position of certain setae, check the Anatomical Atlas of Flies.
The number of online family treatments is growing (see list). Select for example flower flies or milichiid flies to see treatments which extend to all levels of diversity, from the family to the species. Also, the treatments for primitive crane flies and eurychoromyiid flies are complete. You can also find lots of information on Tephritidae (fruit flies) by clicking here. For photos of flies look through the 'Diptera ' image gallery.
Content by F. Christian Thompson