The geometer moths are moths belonging to the family Geometridae of the insect order Lepidoptera, the moths and butterflies. Their scientific name derives from the Ancient Greek γεω (geo) (derivative form of γῆ or γαῖα "the earth"), and μέτρον (métron) "measure" in reference to the way their larvae, or inchworms, appear to measure the earth as they move along in a looping fashion. Geometridae is a very large family, containing around 23,000 described species; over 1400 species from six subfamilies are indigenous to North America alone. A well-known member is the peppered moth, Biston betularia, which has been the subject of numerous studies in population genetics. Several other geometer moths are notorious pests.
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Geometridae in the context of Tympanal organ
A tympanal organ (or tympanic organ) is a hearing organ in insects, consisting of a tympanal membrane (tympanum) stretched across a frame backed by an air sac and associated sensory neurons. Sounds vibrate the membrane, and the vibrations are sensed by a chordotonal organ. Hymenoptera (bees, wasps, ants, etc.) do not have a tympanal organ, but they do have a Johnston's organ.
Tympanal organs have evolved in at least seven different orders of insects. Tympanal organs can 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.
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