Wing

Wing, in biology, one of paired movable appendages by means of which flight may be achieved. Birds, bats, and insects propel themselves through the air by flapping their wings. The extinct reptile pterodactyl also flew in this manner. This type of flight, sometimes called true flight, is distinguished from gliding flight, in which the wings are outstretched to sustain flight with little or no motion. Gliding flight is found among certain fish, mammals, amphibians, and reptiles, and is also employed part of the time by various birds, including hawks, vultures, and gulls.

Among vertebrates, the wing is homologous to the forelimb or arm and assumes many different shapes. The wings of a bird are covered with feathers and form a support and axis to which the muscles that move it are attached. Those of a bat are merely membranes that are spread across modified fingers and are attached to the side of the body to form a patagium. The wings of such so-called flying animals as flying foxes, flying lizards, and the flying squirrel are merely expansions of the skin along the sides of the body to assist the animals in jumping from tree to tree, or from a tree to the ground. Among invertebrates, true wings are found only in insects; they usually consist of two layers of skin supported on hollow tubes, or nervures, are often covered with minute scales, and always communicate with the respiratory system (see Insect). In the flying fish, the flightlike movements are accomplished by means of large pectoral fins that are modified to serve as wings.

Wings are used for many purposes other than for flight. They assist many water birds in diving and swimming by allowing underwater motions analogous to flying; they shield eggs or tender fledglings from rain and hot sun during hatching and brooding; and they serve as weapons for such animals as turkey and spurwinged goose. In birds such as the snipe and hummingbird, and in many insects, the wings make a distinctly audible noise when in flight. Wings are also used by many animals as a means of emotional expression, especially during the mating season. In such cases they are fluttered, elevated, spread, beaten against the body, or clapped together over the back to produce drumming or crackling sounds expressing excitement or serving as signals or challenges.

For the design of wings in airplanes, see Aerodynamics; Airplane.