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Cicadas Print E-mail
ImageCicada is from the Latin, meaning “buzzer” and they are flying, plant-sucking insects of the Order Hemiptera; their closest relatives being leafhoppers, treehoppers, and fulgoroids. The adult insect, sometimes called an imago, is usually 2 to 5 cm (1 to 2 inch) long, although some tropical species can reach 15 cm (6 inch), 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.
Also, commonly overlooked, cicadas have 3 small eyes located on the top of the head between the two large eyes that match the color of the large eyes, giving them a total of five eyes. 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 (72° F) above ambient temperature.
Cicadas are probably best known for their loud acoustic signals or "songs", which the males make using special structures called tymbals, found on the abdomen.
The sound of the cicada love song is the loudest in the insect world and some species register up to 120 decibels. Only the males sing, to attract females for mating. The songs are species-specific, so individuals can locate their own kind when different species share the same habitat. The adult male has two ribbed membranes called tymbals, one on each side of its first abdominal segment. By contracting the tymbal muscle, the cicada buckles the membrane inward, producing a loud click. As the membrane snaps back, it clicks again. The two tymbals click alternately. Air sacs in the hollow abdominal cavity amplify the clicking sounds. The vibration travels through the body to the tympani, which amplify the sound further. A single male makes a noise over 100 decibels, but males aggregate as they sing, creating
a deafening chorus as they fly and sing, landing on sunny branches near the tops of trees. The female responds by doing a "wing flick” which involves a brisk movement of the wings. The male sees and hears the wing flick, and replies with more tymbal clicks.
As the duet continues, the male approaches and begins a new song, called the courtship call. As well as mating and courtship calls, the male makes noise when startled. Pick up a male cicada, and you'll probably hear a good example of the cicada shriek.
There are about 2,000 species of cicadas worldwide, most of them found in tropical or temperate regions. Most of the more than 100 species found in North America have short life cycles, between two and eight years. They are known as annual or dog-day cicadas because they usually emerge during mid to late summer (July and August) and they are dark with green markings. The periodical cicada has protruding red eyes and orange legs; adults have clear wings with orange veins.
All but a few cicada species have multiple-year life cycles, most commonly 2-8 years. In most species, adults are found every year because the population is not developmentally synchronized; these are often called "annual" cicadas.
In contrast, populations of the periodic cicada species are synchronized, so that almost all of them mature into adults in the same year. The fact that periodic cicadas remain locked together in time is made even more amazing by their extremely long life-cycles of 13 or 17 years, and it is not known how they count the years or achieve this synchronization. Periodic cicadas are found in eastern North America and belong to the genus Magicicada. There are seven species -four with 13-year life cycles (including one new species described in 2000), and three with 17-year cycles. The three 17-year species are generally northern in distribution, while the 13-year species are generally southern and midwestern. Magicicada are so well-synchronized developmentally that they are nearly absent as adults in the 12 or 16 years between emergences. When they do emerge after their long juvenile periods, they do so in vast numbers, up to 1.5 million insects per acre, forming much denser aggregations than those usually achieved by cicadas, thus evolving an effective survival strategy to overwhelm predators by sheer volume. Once the predators have eaten to capacity, there are still millions of cicadas left over to produce the next generation. Predator populations cannot build up in response to such a massive
 food supply, because the cicadas appear above the ground only once in every 13 or 17 years. The mass emergence of periodical cicadas provides an unlimited feast for birds, snakes, and mammals. Even humans have been known to eat the harmless insects (Cicadas are not poisonous and do not bite or sting).
Many people know periodic cicadas by the name "17-year locusts" or "13-year locusts", but they are not true locusts, which are a type of grasshopper.
Magicicada cicadas synchronize their life cycles only in local areas. There are 12 broods, or year classes, among the 17-year cicadas and three broods of 13-year cicadas so that in almost any given year it is possible to find adult periodic cicadas somewhere in the U.S. In Costa Rica, the local name for cicada is “chicharra” and they appear in the Costa Rican summer in January, February and March.
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