Sound Amplifiers – Cicadas

Cicada is an insect belonging to the order Hemiptera and family Cicadoidea. The insect is characterized by presence of large eyes placed apart on the head with transparent veined wings. About 2,500 species are known and may are yet to be classified. They dwell in tropical to temperate habitats and can be easily distinguished from other insects because of their large size and acoustic features. They are sometimes confused with locusts. They are commonly known as jar flies of July flies in Southeastern United States and heat bugs in Canada. They are related to spittlebugs and leafhoppers. Cicadas are very kind to humans and generally do not bite or sting humans and can do so only by a mistake. They bear a long proboscis for feeding just under their heads for feeding on the plan sap. If the proboscis is inserted into the human’s body it is painful but not harmful.

Cicadas are known to cause damage to the cultivated crops, shrubs and trees by forming scars. The female lays eggs on the leaves. They are consumed as food in many parts of the world like Burma, Malaysia, China, and Latin America. The female is very much relished as food. The name cicada has been derived from a Latin word meaning buzzer. The adult insect is also known as imago and measures 2-5 cm in length. Some species can reach to a length of 15 cm also. They have large eyes placed apart on the head and short antennae are there in front of the eyes and the wings are membranous. They have three ocelli just in front of the eyes that resemble with the colour of the eyes. Desert species are known to cool their bodies by sweating while other species are known to raise their body temperature to about 22°C above ambient temperature.

Male cicadas are known to generate loud sounds as they carry tymbals on the sides of their abdominal bases. The sounds produced by them are not stridulation as seen in the crickets. Tymbals are actually the regions of exoskeleton that are modified to become membranous and are provided with ribs. Contraction of the internal tymbal muscles causes a clicking sound. As these muscles relax the tymbals return to their original position and produce another clicking sound. The interior of the male’s abdomen is hollow so it can amplify the sound. The insect uses these membranes rapidly and the enlarged chambers derived from the trachea serve as resonance chambers which help to amplify the sound. They maintain the intensity of sound by positioning their abdomen. Each species is demarcated by a different sound. For the generation of the sound the average temperature must e somewhat higher than the ambient temperature. Sound is best produced in the hotter days.

Only males are known to produce sound but both the sexes bear tympana. They produce a sound up to 120 dB. The sound generated by cicadas can lead to permanent hearing loss in humans. After mating the female lays eggs in the bark of a tree. She lays hundreds of eggs which hatch into tiny nymphs that drop to the ground. They make burrows. The life cycle takes 2-5 years to complete. Some species may take 13-17 years to complete their life cycle. Birds and wasps are known to be their top most predators. They protect themselves by the phenomenon known as predator satiation. About 220 species of cicadas have been reported from Australia.

Cicadas are very interesting creatures and people of Japan keep them in cages as pets.