Insect Order Diptera - true flies
Although many winged insects are commonly called "flies," the name is strictly applicable only to members of the Diptera. It is one of the largest insect orders and contains over 85,000 species; all are relatively small and have soft bodies.  Mouth parts are of the sucking type, but there is great variation.  Some, like the blood-suckers, are serious pests.  Flies are beneficial as scavengers and predators or other insect pests.
Diptera are divided into three large groups: Nematocera (crane flies, midges, gnats, and mosquitoes); the Brachycera (horse flies, robber flies and bee flies); and Cyclorrhapha (flies that breed in vegetable or animal material, both living and dead.)