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.
Notwithstanding pest label, many fly families can be considered beneficial insects that pollinate plants and prey on insect pests. This brief presentation provides pictures and descriptions of some basic fly types to help answer beginning fly identification questions.
The fly is one of the most common and diverse groups of animals on the planet. Although they so often share an antagonistic relationship with humans as an annoyance or a potential carrier of diseases, these insects also serve many important ecological roles.
A normal fly has two flight wings on its thorax and a pair of halteres. The halteres, which evolved from the hind wings, act as flight sensors: they are balance organs.
Mechanical flight is the use of a machine to fly. These machines include aircraft such as airplanes, gliders, helicopters, autogyros, airships, balloons, ornithopters as well as spacecraft.