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Cicadas are a type of insects with the ability to fly in their mature form. They are often heard but not seen, and many are familiar with their song during July and August as the males stretch and release their tymbals, causing a stridulation that can reach up to 106 decibels.
Species vary in appearance, but all can be identified by the sound they make and by their transparent veined wings. Their large eyes are wide apart and their antennae short. Most adult cicadas are 1 to 2 inches (2 to 5 cm) long. However, some, like the Malaysian Pomponia imperatoria, are a great deal larger at 6 inches (15.24 cm). There are thousands of different species in the world, 200 alone in the US, but the group as a whole can be broken into two sets based on life cycle: periodical and annual.
Both annual and periodical cicadas begin life in roughly the same way. The females dig a small opening in a tree and lay eggs, which have the same appearance as rice grains. At first, the young suck fluids from the tree, but as they mature, they leave the tree opening and dig into the ground until they find a tree root to which they can attach. In this stage they are called nymphs, and they stay underground attached to the root until they shed their exoskeleton and become mature adults, or imagoes.
What varies between annual and periodical cicadas is the length of time the nymph stays underground, feeding on the fluid from tree roots. Annual cicadas tend to live underground for between two to seven years as nymphs before becoming imagoes. On the other hand, periodical cicadas can spend up to 17 years as nymphs before emerging to spend their two months of maturity as adults.
Another distinction between the two types is the difference in the way they emerge. Annual cicadas tend to reach adulthood and emerge in small numbers. Conversely, periodicals like the US Magicicada hatch in huge numbers. Scientists suggest this massive release is due to evolutionary survival tactics. The large number of periodical imagoes will satiate predators, but will also assure that the species can perpetuate itself.
The emergence of periodical imagoes has a somewhat mystical quality. A child of one, for example, will not see another emergence until he or she is an adult. In fact, scientists have observed that the life cycle of cicadas seems uniquely designed to ensure survival. Both annuals and periodicals tend to hatch and grow to maturity in prime numbers, 2, 3, 5, 7, and up to 17. The fact that predators like birds and moles cannot depend upon a yearly supply of these insects in their diet makes them less likely to be considered as part of the food chain for nonhuman animals.
An unlikely predator of the cicada is human beings. Many Native American tribes, Japanese, Australians, and Papua New Guineans prize cicadas as a culinary delight. The Ancient Greeks also enjoyed these insects as a snack. In China, a tea is made from the shed skin of nymphs and given to crying babies to quiet them.
Whether one eats them, or simply appreciates the singing of cicadas, the lives of these insects holds mystery for most cultures past and present. Some, like the Navajo, view the cicada as a sign of rebirth. Japanese kite makers design some kites in the form of a cicada, and many other Asian cultures view the insects as a sign of good fortune. Most cultures have celebrated this insect in songs, poetry, or folklore, so the intricate life of the cicada clearly maintains a special place in our view of the world.