Tuesday, March 19, 2013

The cicada

Cicada (Cicada orni)

Cicadas are insects with a large eyes and transparent wings. The species found in Malta, known as weżieq ta’ bi nhar, can be heard calling throughout the summer wherever there are trees even in urban areas. It is one of about 2,500 species of cicada found in temperate and tropical climates around the world. Cicadas are harmless to humans as they do not bite or sting but they can damage crops, trees and shrubs.

The noise of the cicada is made by means of a pair of organs known as timbals which are found on the side of the abdomen. These consist of regions of the exoskeleton that are modified to form a complex membrane with thin membranous portions and thickened ribs. By contracting the internal muscles attached to the timbals these are buckled inwards making a clicking sound. As the muscles are relaxed the timbals go back to their original position and make another click. This movement is repeated rapidly to make a continuous sound which is amplified in enlarged chambers derived from the tracheae which serve as resonance chambers. Every species of cicada has a particular song by which it can be identified.

Cicadas normally live in hot environments and are often most active during the hottest times of the day.
Only males can sing but both males and females have organs to enable them to detect sound. In some species the male can disable this organ while singing.  Some cicadas are able to produce very loud sounds which are considered to be amongst the loudest of all insect-produced sounds while some small species have songs which are so high pitched that they are inaudible to humans.

In addition to the mating song, many species including the species found in the Maltese islands, have a distress call which is usually a somewhat broken and erratic sound emitted when the individual is seized.
A number of species also have a courtship song which is produced after a female has been attracted to a male by its calling song.

This article was published in The Times on 16 September 2009.

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