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Cicada
Cicada

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 they leave behind.

Cicadas do not bite or sting, are benign to humans but can be pests to several cultivated crops. 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.

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.

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 (SPL) 'at close range', among the loudest of all insect-produced sounds. Conversely, 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, e.g., such as the North American genus, Magicicada, which has a number of distinct 'broods' that go through either a 17-year or, in the American South, a 13-year life cycle. 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. Both 13 and 17 are prime numbers, so while a cicada with a 15-year life cycle could be preyed upon by a predator with a three- or five-year life cycle, the 13- and 17-year cycles allow them to stop the predators falling into step. 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.

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