The most distinctive feature of cicadas is their ability to sing. During the peak of summer their massed chorus can be deafening. Only the males sing, mainly to court females.
How cicadas sing
Male cicadas use their tymbals to produce sound. These are ribbed membranes on each side of the base of the abdomen. Each tymbal is attached by a tendon to a powerful muscle. As the muscle contracts it buckles the shape of the tymbal, much as when the domed lid of a jar is first unsealed, causing a burst of sound called a pulse. When the muscle is relaxed the tymbal pops back into shape. Rapid and repeated muscle contraction produces the distinctive cicada call.
The digestive and reproductive organs are reduced in the male, making room for large air sacs in the abdomen that amplify the song. Variations in songs are the result of differences in the sound frequency (which is dependent on the tymbal structure), the sound pulse rate and pattern, and the volume.
Differences between species
Cicada songs vary widely between species, ranging from raucous screeches to more restrained, faint chirps. These are sometimes so distinctive that individual species may be identified by song alone. Some New Zealand cicadas (genus Amphipsalta) also make a sharp clapping or clicking sound by rapidly tapping their wings against the branch on which they are perched.
A deafening downpour
The widespread chorus cicada is New Zealand’s largest species (wingspans can reach 8 centimetres), and its loudest, with the adults emerging en masse and singing in chorus. Their Māori name is kihikihi wawā – wawā meaning ‘to roar like the sound of heavy rain’.
Getting the message
Sound is received by males and females through a pair of membranous plates at the base of the abdomen called tympana. These are covered by protective plates called opercula, which extend from the base of the thorax. Capsules containing hearing organs are connected to the opercula.
Females are able to detect the direction of sound, and so can track the singing males. Males, in contrast, are only able to detect the closeness of competing males.