The Cicada

Mar 28, 2010 Features / Columnists, Interesting Creatures in Guyana

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A cicada is an insect of the order Hemiptera, suborder Auchenorrhyncha, in the superfamily Cicadoidea, with large eyes wide apart on the head and usually transparent, well-veined wings. There are about 2,500 species of cicada around the world, and many remain unclassified. Cicadas live 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.
Cicadas are sometimes colloquially called “locusts”, although they are unrelated to true locusts, which are a kind of grasshopper. They are also known as “jar flies”. Cicadas are related to leafhoppers and spittlebugs. In parts of the southern Appalachian Mountains in the United States, they are known as “dry flies” because of the dry shell that they leave behind.
Cicadas are benign to humans and do not bite or sting, but can cause damage to several cultivated crops, shrubs, and trees. Many people around the world regularly eat cicadas; the female is prized, as it is meatier. Cicadas have been (or are still) eaten in Ancient Greece, China, Malaysia, Burma, Latin America, and the Congo. Shells of cicadas are employed in the traditional medicines of China. The name is a direct derivation of the Latin cicada, meaning “buzzer”. The adult insect, sometimes called an imago, is usually two to five centimeters (one to two inches) long, although some tropical species can reach 15 cm (6 in), e.g. Pomponia imperatoria from Malaysia. 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. Also, commonly overlooked, cicadas have three small eyes, or ocelli, located on the top of the head between the two large eyes that match the colour of the large eyes.
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 22 °C (40 °F) above ambient temperature.
Male cicadas have loud noisemakers called “timbals” on the sides of the abdominal base. Their “singing” is not the stridulation (where two structures are rubbed against one another) of many other familiar sound-producing insects like crickets: 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. Additionally, each species has its own distinctive song.
Average temperature of the natural habitat for this species is approximately 29 °C (84 °F). During sound production the temperature of the tymbal muscles were found to be slightly higher. Cicadas like heat and do their most spirited singing during the hotter hours of the day. 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.
Some small species have songs so high in pitch that the noise is inaudible to humans. Species have different mating songs to ensure they attract the appropriate mate. 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.
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. Some species have much longer life cycles. Cicadas live underground as nymphs for most of their lives, at depths ranging from about 30 cm (1 ft) up to 2.5 m (about 8½ ft). 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 molt (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 are commonly eaten by birds, but Massospora cicadina (a fungal disease) is the biggest enemy of cicadas. Another known predator is the cicada killer wasp.
In eastern Australia, the native freshwater fish Australian bass are keen predators of cicadas that crash-land on the surface of streams.
Some species of cicada also have an unusual defense mechanism to protect themselves from predation, known as predator satiation: by many emerging at once, whereas there are no cidadas around for much of the year, essentially, the number of cicadas in any given area exceeds the amount predators can eat; all available predators are thus satiated, and the remaining cicadas can breed in peace.
(Source: Wikipedia – The Free Online Encyclopedia)

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