The Bladder Grasshopper of South Africa, Bullacris membracioides, has a sound detection system that can detect mating calls at great distance. This grasshopper does not have a tympanum like many of the grasshopper species. Instead it has a series of 12 chordotonal organs in the first 6 segments of its abdomen (one on each side). The organs in the first abdominal segment are the most sensitive: each contains 2000 sensilla. The posterior five pairs contain only 11 sensilla and are less sensitive, detecting sounds of 60 db at about of 100 meters.
In these grasshoppers, both the males and the females call as part of their mate finding behavior. However, the females will only call if the posterior receptors detect a male. This limits calling by females until she is within 100 meter of the males and limits the ability of predators and parasitoids to eavesdrop.
MOIRA J. VAN STAADEN, MICHAEL RIESER, SWIDBERT R. OTT, MARIA A. PABST AND HEINER ROMER. (2003) Serial Hearing Organs in the Atympanate Grasshopper Bullacris membracioides. THE JOURNAL OF COMPARATIVE NEUROLOGY 465:579–592.