Cicada Song

Last week, I had been to Nagarhole, Rajiv Gandhi National Park (see map) and got to watch and learn from several of the marvellous creatures of nature. Cicada was one, which we frequently got the chance to observe. I was of the belief that they make their noise by rubbing their legs as the crickets and locusts do! I was wrong! They make their noise using special body part called tymbals. if you are interested in learning more about these magnificent insects, please read further!


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The Insect
Cicada (sih-kay-duh) is an insect of the order with large eyes wide apart on the head and usually transparent, well-veined wings. The adult insect, sometimes called an imago, is usually 2 to 5 cm long, although some tropical species can reach 15 cm. Cicadas have prominent eyes set wide apart on the sides of the head, short antennae protruding between or in front of the eyes, and membranous front wings. Over 2,500 species of cicada are found in temperate to tropical climates where they are among the most widely recognized of all insects, mainly due to their large size and remarkable acoustic talents.

Harmless
Although the Cicadas appear large and scary, they do not bite or sting, are benign to humans, and are not considered pests. Some people in Ancient Greece, China, Malaysia, Burma, Latin America and the Congo eat cicadas: the female is prized as it is meatier. Some of them are considered as pests, when they swarm the area in large numbers.

Did You Know?
Desert cicadas are also among the few insects known to cool themselves by sweating, while many other cicadas can voluntarily raise their body temperatures as much as 22oC above ambient temperature.

The Cicada Song

Male cicadas have loud noisemakers called "timbals" on the sides of the abdominal base. Unlike other familiar sound-producing insects like crickets their "singing" is not created by the stridulation (where two structures are rubbed against one another). The timbals are regions of the exoskeleton that are modified to form a complex membrane with thin, membranous portions and thickened "ribs". Contracting the internal timbal muscles produces a clicking sound as the timbals buckle inwards. As these muscles relax, the timbals return to their original position producing another click. The interior of the male abdomen is substantially hollow to amplify the resonance of the sound. A cicada rapidly vibrates these membranes, and enlarged chambers derived from the tracheae make its body serve as a resonance chamber, greatly amplifying the sound. They modulate their noise by wiggling their abdomens toward and away from the tree that they are on. Also, each species is known to have its own distinctive song.



Although only males produce the cicadas' distinctive sound, both sexes have tympana, which are membranous structures used to detect sounds and thus the cicadas' equivalent of ears. Males can disable their own tympana while calling. Adult cicadas have a sideways-ridged plate where the mouth is in normal insects.

Some cicadas produce sounds up to 120 dB "at close range", among the loudest of all insect-produced sounds. Conversely, some small species are known to have songs in such high pitch, that the noise is inaudible to humans. Species have different mating songs to ensure they attract the appropriate mate. Male cicadas are also capable of making a loud squawk when disturbed. It is believed that such squawking may be effective in deterring predators. Males of many species tend to gather which creates a greater sound intensity and protects against avian predators. It can be difficult to determine which direction(s) cicada song is coming from, because the low pitch carries well and because it may, in fact, be coming from many directions at once, as cicadas in various trees all make noise at once.

In addition to the mating song, many species also have a distinct distress call, usually a somewhat broken and erratic sound emitted when an individual is seized. A number of species also have a courtship song, which is often a quieter call and is produced after a female has been drawn by the calling song.

The song of the cicada is a favourite sound effect used by filmmakers and animators as a means of representing silence, pathos, and the great outdoors.

Life Cycle

After mating, the female cuts slits into the bark of a twig, and into these she deposits her eggs. She may do so repeatedly, until she has laid several hundred eggs. When the eggs hatch, the newborn nymphs drop to the ground, where they burrow. Most cicadas go through a life cycle that lasts from two to five years. These long life cycles are an adaptation to predators such as the cicada killer wasp and praying mantis, as a predator could not regularly fall into synchrony with the cicadas.

The insects spend most of the time that they are underground as nymphs at depths ranging from about 30 cm up to 2.5 m. The nymphs feed on root juice and have strong front legs for digging. In the final nymphal instar, they construct an exit tunnel to the surface and emerge. They then moult (shed their skins), on a nearby plant for the last time and emerge as adults. The abandoned skins remain, still clinging to the bark of trees. Cicadas inhabit both native and exotic plants including tall trees, coastal mangroves, urban gardens and desert shrubs.