There are approximately 16,000 species of flies in America. All of them have two wings thus they belong to the order Diptera. Since they just have two wings, flies land frequently and subsequently can store and deposit a huge number of bacteria each time they land.
fly, (order Diptera), any of a large number of insects characterized by the use of only one pair of wings for flight and the reduction of the second pair of wings to knobs (called halteres) used for balance. The term fly is commonly used for almost any small flying insect.
However, in entomology the name refers specifically to the approximately 125,000 species of dipterans, or “true” flies, which are distributed throughout the world, including the subarctic and high mountains.
Dipterans are known by such common names as gnats, midges, mosquitoes, and leaf miners, in addition to numerous sorts of flies, including the horse fly, housefly, blow fly, and fruit, bee, robber, and crane flies. Many other species of insects are called flies (e.g., dragonflies, caddisflies, and mayflies), but their wing structures serve to distinguish them from true flies.
Many species of dipterans are of great importance economically, and some, such as the common housefly and certain mosquitoes, are of importance as disease carriers. See dipteran.
Most homes and businesses eventually experience problems with indoor flies. Though relatively few kinds of flies can breed and complete their life cycles inside a structure, each indoor fly species is unique. For that reason, it’s important to correctly identify the type of fly in your home in order to control it.