The functional units of insect tympanal ears, the chordotonal organs, have evolved from preexisting chordotonal organs in species lacking ears. This evolutionary change has been accompanied by pronounced behavioral changes; in the case of moths, the tympanal ear has allowed the moths to detect the high-frequency calls of echolocating insectivorous bats and execute changes in their flight path to avoid predation. Since the chordotonal organ of eared moths in the superfamily Noctuoidea are composed of only one or two sensory cells, they provide a simple system for our research on the neural basis of evolution of auditory behavior in moths. The identified ancestral homologue to the noctuoid tympanal ear is a chordotonal organ at the wing base of earless (atympanate) moths. Using Manduca sexta as a model for the atympanate moths, we report on the neuroanatomical changes between the atympanate and tympanate species, by describing the peripheral changes to the number of axons, axon diameters and central projection patterns of the chordotonal organ afferents. These results provide the first insight into the ancestral neural circuitry of the noctuoid moth ear. Physiological recordings show that chordotonal organs of tympanate and atympanate moths respond differently to sound. Physiological recordings of M. sexta obtained during stationary flight and passive stimulation of the wings and cuticle, show that the atympanate chordotonal organ is also responsive to vibrations produced during flight behavior. This provides the initial evidence for the hypothesis that the chordotonal organ is a putative proprioceptor monitoring wing movement.