Flies are found throughout the world, and exist in areas from the Arctic to the rain forests on the equator. Benefits of flies to mankind. As in other kinds of insects, there are in the Order Diptera many flies that are beneficial to mankind. Flies that visit flowers are helpful in the pollination of flowering plants. The maggots of hover flies are welcomed by gardeners because they feed on aphids, reducing numbers of those pests.
Many flies are parasitic, feeding on moth caterpillars, beetle grubs, and other pest species.
Some species of gall midges, fruit flies and other families have been introduced to North America as weed biocontrol agents. Species of Drosophilidae have been used extensively in studies of genetics because of their short lifespans, giant salivary gland chromosomes, and ease of culturing. Detriments of flies to mankind. Unfortunately, some flies, especially mosquitoes, transmit some of the most destructive diseases, notably malaria and yellow fever. Some flies, such as the Mediterranean Fruit Fly, attack and spoil citrus and other fruits.