7 March 2011

Cicada (Cicadoidea)

Here is another interesting photograph from my holiday ...

Figure 1:  Discarded cicada skin.

Cicada (pronounced /sɪˈkeɪdə/ or pronounced /sɪˈkɑːdə/) 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 often colloquially called locusts, although they are unrelated to true locusts, which are a kind of grasshopper. They are also known as "jar flies" and, regionally, as July flies in the Southeastern United States, and as "heat bugs" in Canada and the Midwest. 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 in normal circumstances and do not bite or sting in a true sense, but may in fact sting after mistaking a person's arm or other part of their body as a tree or plant limb and attempt to feed.  Cicadas have a long proboscis under their head that they use for feeding on tree sap, and if they attempt to inject it into a person's body it can be painful, but is in no other way harmful. This sting is not a defensive reaction and should not be mistaken for aggression; it is extremely uncommon, and usually only happens when they are 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; 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". In classical Greek, it was called a tettix, and in modern Greek tzitzikas—both names being onomatopoeic.
Male cicadas have loud noisemakers called "tymbals" on the sides of the abdominal base. Their "singing" is not the stridulation (where one structure is rubbed against another) of many other familiar sound-producing insects like crickets: the tymbals are regions of the exoskeleton that are modified to form a complex membrane with thin, membranous portions and thickened "ribs". Contracting the internal tymbal muscles produces a clicking sound as the tymbals buckle inwards. As these muscles relax, the tymbals 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 positioning their abdomens toward or away from the substrate. 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 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.

Some cicadas produce sounds up to 120 dB (SPL) "at close range", among the loudest of all insect-produced sounds. This is especially notable as their song is technically loud enough to cause permanent hearing loss in humans, should the cicada sing just outside the listener's ear (unlikely). 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.

Cicada song

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