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 and plants, and therefore are not considered pests. 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.
In 2004, "cicada" ranked 6th in Merriam-Webster's Words of the Year.
The largest cicadas are in the genera Pomponia and Tacua. There are some 200 species in 38 genera in Australia, about 450 in Africa, about 100 in the Palaearctic and exactly one species in England, the New Forest cicada, Melampsalta montana, widely distributed throughout Europe. There are about 150 species in South Africa.
Most of the North American species are in the genus Tibicen - the annual or dog-day cicadas (so named because they emerge in late July and August[[Cicada# note-0|  ]]). The best-known North American genus is Magicicada, however. These periodical cicadas have an extremely long life cycle of 13 to 17 years and emerge in large numbers. Another American species is the Apache cicada, Diceroprocta apache.
Australian cicada's can differ from many other cicadas because of their diversity of climate and terrain. Some cicadas in Australia are found in Tropical Islands, Tropical Wetlands, High and Low Deserts, Cold Coastal Beaches around Tasmania, Alpine Mountains in New South Wales and Victoria, Large cities like Sydney, Melbourne and Brisbane and Tasmanian Highlands and Snow Fields.
Thirty-eight species from five genera populate New Zealand, and all are endemic to New Zealand and the surrounding islands (Norfolk Island, New Caledonia). Many New Zealand cicada species differ from those of other countries by being found high up on mountains.
The adult insect, sometimes called an imago, is usually 2 to 5 cm (1 to 2 inches) long, although some tropical species can reach 15 cm (6"), 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. 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 above ambient temperature.
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 a summer 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. 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.
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.
In eastern Australia, the native freshwater fish Australian bass are keen predators of cicadas that crash-land on the surface of streams.
Being principally tropical insects, most Australian species are found in the northern states. However, cicadas occur in almost every part of Australia: the hot wet tropical north; Tasmanian snowfields; Victorian beaches and sand dunes such as Torquay and deserts. According to Max Moulds of the Australian Museum in Sydney: "the 'green grocer' is unusual in its ability to adapt perfectly to the urbanized environment." Cicada sounds are a defining quality of Melbourne, Sydney and Canberra during late spring and the summer months.
Cicadas inhabit both native and exotic plants including tall trees, coastal mangroves, suburban lawns and desert shrubbery. The great variety of flora and climatic variation found in north-eastern Queensland results in its being the richest region for the spread of different species. The area of greatest species diversity is a 100 km (60 mi) wide region around Cairns. In some areas they are preyed on by the cicada-hunter (Exeirus lateritius) which stings and stuns cicadas high in the trees, making them drop to the ground where the cicada-hunter mounts and rides them, pushing with its hind-legs, sometimes over a distance of a hundred yards, till they can be shoved down into its burrow, where the numb cicada is placed onto one of many shelves in a 'catacomb', to form the food-stock for the wasp grub that grows out of the egg deposited there.
A summer insect (at least in temperate countries), the cicada has represented insouciance (i.e. nonchalance or indifference) since antiquity. Jean de La Fontaine began his collection of fables Les fables de La Fontaine with the story La Cigale et la Fourmi (The Cicada and the Ant) based on one of Aesop's fables: in it the cicada spends the summer singing while the ant stores away food, and finds herself without food when the weather turns bitter.
In The Tale of Genji, the title character poetically likens one of his many love interests to a cicada for the way she delicately sheds her scarf the way a cicada sheds its shell when molting. They are also a frequent subject of haiku.
In China the phrase 'to shed off the golden cicada skin' is the poetic name of the tactic of using deception to escape danger, specifically of using likenesses/decoys (leaving the old shell) to fool enemies. In the Chinese classic Journey to the West, the protagonist Priest of Tang was named the Golden Cicada, in this context the multiple shedding of shell of the cicada symbolizes the many stages of transformations required of a person before all illusions has been broken and one reaches enlightenment.