A true fly has only one set of wings. All flies are known disease carriers, many of which can be transmitted to humans. Flies typically breed in garbage, excrement of animals and humans, sewers, compost piles, and any other place where matter is decaying. This enables them to pick up various kinds of diseases which can be transmitted to people by biting or by landing on food, where the bacteria and viruses are released. Since flies are able to transmit disease so easily, it is necessary to seek insect control quickly. The diseases that they can carry include malaria, yellow fever, encephalitis, dengue fever, and more.