According to a recent study:
Bushcrickets, also known as katydids, are those green grasshopper-like insects that fascinate children because of their leaf-like camouflage. Using Optical Coherence Tomography (OCT), the European team obtained detailed images of the hearing organs of bushcrickets. The hearing organ on these orthopterans are located on the tibia just below the knee. Called the crista acoustica (CA), this organ, only 0.9 mm long, contains a series of sensory dendrites of decreasing length from the proximal to distal ends of the CA, oriented perpendicular to it. They look like piano strings, and presumably perform a similar function to the hair cells in the Organ of Corti of the mammalian cochlea. The ventral ends of the dendrites in the CA are embedded in the distal wall (DW), analogous to the basilar membrane in the cochlea. The dorsal ends of the dendrites are connected to cap cells which resemble the hair cells in vertebrate cochleae, where acoustic transduction to electric (neural) signals take place.
Other than location (in the heads of vertebrates and on the legs of insects), the functional similarities of the CA to the mammalian cochlea are striking, except that the cochlea is 40 times as long as the insect hearing organ! It’s a remarkable example of convergence already, and there is more to come.
Evolution News, “Hear This: Cricket Ears Evolved Like Vertebrate Ears” at Evolution News and Science Today (December 15, 2021)
The paper is open access.