Unlike humans, grasshoppers do not have ears on the side of their head. Like the ears of people, the grasshopper sound detector is a thin membrane called a tympanum, or “eardrum”. In adults, the tympanum is covered and protected by the wings, and allows the grasshopper to hear the songs of its fellow grasshoppers.
The grasshopper tympanum is adapted to vibrate in response to signals that are important to the grasshopper. Male grasshoppers use sounds to call for mates and to claim territory. Females can hear the sound that males make and judge the relative size of the male from the pitch of the call (large males make deeper sounds). Other males can hear the sounds and judge the size of a potential rival. Males use this information to avoid fights with larger male grasshoppers or to chase smaller rivals from their territory.