Most praying mantids have a single ear located in the ventral midline of the metathorax. It comprises an auditory chamber, two tympana, and four sensory organs. Mantids have sensitive hearing for frequencies >20 kHz. Their sister group, cockroaches, do not have tympanate hearing, and comparison with mantids can provide clues to the transition from earless to eared. Despite minimal similarity in appearance, the cuticular components of the mantis ear have clear cockroach homologues, including a ‘proto-tympanum’. Conversion to the mantis ear would mainly require a medial shift and a rotation of the homologous structures. Cockroach Nerve 7 (N.7) is virtually identical to the tympanal nerve in bifunctional organization, number of axons, absence of efferent axons, and branching pattern. The CNS terminations of N.7 are also nearly identical in the two insects with the exception of an additional branch from <10 axons in mantids. Functionally, the transition has been from proprioception dominated by external socketed hairs to vibration detection entirely by internal chordotonal sensilla. Thus, the evolution of a ‘new’ auditory system is unlikely to require new components. Mantis hearing may have arisen from relatively simple changes in cuticle geometry, a different balance of sensory sources in the periphery, and relatively small anatomical alterations in the CNS.