In the fly family (Diptera) the first pair of wings is reduced to form so-called halteres. They act as counterbalances, almost like a gyroscope during flight. In crane flies this degenerated first wing pair is clearly visible. The fly group 'order' is called Diptera, which means 'two winged' because they have only one pair of wings.

Zoom in to see the head of the crane fly

See the attractive wings of a fruit fly