A hearing organ in insects, consisting of a membrane (tympanum) stretched across a frame backed by an air sac. Sounds vibrate the membrane, and the vibrations are sensed by a chordotonal organ. Tympanum may mean: The eardrum; or A sculpted panel that stands within the recessed area formed by a larger arch above the doors to a church or similar building, especially in Romanesque and Gothic architecture; or A single drum in the orchestral percussion section usually called timpani. ...

Tympanal organs occur in just about any part of the insect: the thorax, the base of the wing, the abdomen, the legs, etc., depending on the group of insects. The structures are thought to have evolved independently many times. As a result, their position and structures are often used to help determine the taxonomy of the species. For example, all members of the Geometridae share distinctive paired abdominal tympanal organs that open towards the front side of the first abdominal segment. Within the organ, particular structures vary in shape and are used to indicate shared ancestry of subfamilies. In other families of Lepidoptera having abdominal tympanal organs, the opening may be in a different orientation and the structures differ in shape. Author: Leach, 1815 Type species: Geometra papilionaria (large emerald moth) Diversity: 2,000? genera 26,000 species Subfamilies Alsophilinae Archiearinae Desmobathrinae Ennominae Geometrinae Larentiinae Oenochrominae Orthostixinae Sterrhinae Genera Geometra (etc) Inchworm redirects here. ...

References

Scoble, MJ. 1992. The Lepidoptera: Form, function, and diversity. Oxford Univ. Press.