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Cicadas (// or //) are insects in the order Hemiptera, suborder Auchenorrhyncha (which was formerly included in the now invalid suborder called "Homoptera"). Cicadas are in the superfamily Cicadoidea. Their eyes are prominent, though not especially large, and set wide apart on the anterior lateral corners of the frons. The wings are well-developed, with conspicuous veins; in some species the wing membranes are wholly transparent, whereas in many others the proximal parts of the wings are clouded or opaque and some have no significantly clear areas on their wings at all. About 2,500 species of cicada have been described, and many remain to be described. 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 unique sound. Cicadas are often colloquially called locusts, although they are unrelated to true locusts, which are various species of swarming grasshopper. Cicadas are related to leafhoppers and spittlebugs.
Cicadas are benign to humans under normal circumstances and do not bite or sting in a true sense, but may mistake a person's arm or other part of their body for a tree or plant limb and attempt to feed. Cicadas have long proboscises under their heads which they insert into plant stems in order to feed on sap. Bites can be painful if a cicada attempts to pierce a person's skin, but they are unlikely to cause other harm. Bites are unlikely to be a defensive reaction and are rare, usually occurring when a cicada is allowed to rest on a person's body for an extended amount of time.
Cicadas can cause damage to several cultivated crops, shrubs, and trees, mainly in the form of scarring left on tree branches while the females lay their eggs deep in branches.
Many people around the world regularly eat cicadas. They are known to have been eaten in Ancient Greece as well as China, Malaysia,Burma, Latin America, and the Congo. Female cicadas are prized for being meatier. Shells of cicadas are employed in the traditional medicines of China
Average temperature of the natural habitat for the South American species Fidicina rana is approximately 29 °C (84 °F). During sound production, the temperature of the tymbal muscles was found to be significantly higher. Cicadas sing most actively in hot weather and do their most spirited singing during the hotter hours of a summer day, in a roughly 24-hour cycle.The "singing" of male cicadas is not stridulation such as many familiar species of insects produce — for example crickets. Instead male cicadas have a noisemaker called a tymbal below each side of the anterior abdominal region. The tymbals are structures of the exoskeleton formed into complex membranes with thin, membranous portions and thickened ribs. Contraction of internal muscles buckles the tymbals inwards, producing a click; on relaxation of the muscles the tymbals return to their original position, producing another click. The male abdomen is largely hollow, and acts as a sound box. By rapidly vibrating these membranes a cicada combines the clicks into apparently continuous notes, and enlarged chambers derived from thetracheae serve as resonance chambers, with which it amplifies the sound. The cicada also modulates the song by positioning its abdomen toward or away from the substrate. Partly by the pattern in which it combines the clicks, each species produces its own distinctive mating songs and acoustic signals, ensuring that the song attracts only appropriate mates.
Although only males produce the cicadas' distinctive sound, both sexes have tympana, membranous structures by which they detect sounds. They are the cicadas' equivalent of ears. Males disable their own tympana while calling, thereby preventing damage to their hearing; this is necessary partly because some cicadas produce sounds up to 120 dB (SPL), among the loudest of all insect-produced sounds. The song is loud enough to cause permanent hearing loss in humans should the cicada sing just outside the listener's ear. In contrast, some small species have songs so high in pitch that the noise is inaudible to humans.
To the human ear, and presumably to some predators, it often is difficult to tell where a cicada song is coming from; the pitch is nearly constant, the song sounds continuous to the human ear, and cicadas sing in scattered groups. If a singing male becomes alarmed on the approach of a possible enemy, it softens its song so that the attention of the listener gets distracted to neighbouring louder singers, creating a confusing ventriloqual effect.
In addition to the mating song, many species have a distinct distress call, usually a broken and erratic sound that the insect emits when seized or panicked; at the same time it is likely to squirt waste liquid from the sap that it had been sucking, possibly distracting certain classes of attacker. Some species also have courtship songs, generally quieter, and produced after a female has been drawn by the calling song. Males also produce encounter calls, whether in courtship or to maintain personal space within choruses.