Dipteran insects, also known as true flies, play diverse roles in the environment. As larvae, maggots break down and redistribute organic matter, with their waste products providing nutrients for plants and other organisms. Many dipteran larvae and adult flies serve as an important food source for animals such as fish, birds, amphibians, spiders, and other insects, and thus play an essential role in food chains. Some flies also function as pollinators of plants.
A number of fly species are important pests or vectors of disease. Several mosquito species, for example, spread serious diseases such as malaria, yellow fever, Zika fever, filariasis, chikungunya fever, and dengue. Tsetse flies, bot flies, and blow flies are also harmful to humans and other animals. Screwworms threaten wild and agricultural animals throughout their range. Fruit flies are agricultural pests that can cause significant losses to fruit crops.