Magicicada
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[Photo] A 17-year Periodical cicada (Genus Magicicada) on tree near Chicago il. Date 24 May 2007. Photo by Zzaakk.

Magicicada is the genus of the 13- and 17- year periodical cicadas of eastern North America. These insects display a unique combination of long life cycles, periodicity, and mass emergences. They are sometimes called "seventeen-year locust"s, but they are not locusts; locusts belong to the order Orthoptera.

Taxonomy
There are seven recognized species. Three species have a 17-year cycle:

M. cassini (Linnaeus, 1758)
M. septendecim (Fisher)
M. septendecula (Alexander and Moore, 1962)

Four more species follow a 13-year cycle:

M. neotredecim (Marshall and Cooley, 2000)
M. tredecim (Walsh and Riley, 1868)
M. tredecassini (Alexander and Moore, 1962)
M. tredecula (Alexander and Moore, 1962)

Generally, the 17-year cicadas are distributed more in the northern states of the eastern United States, while the 13-year cicadas occur in the southern states.

Description
Periodical cicadas are slightly smaller than other, annual cicadas. Imagines have a size of 2.5 to 3 cm (1 to 1.2 inches). They are black, with red eyes and yellow or orange stripes on the underside. The wings are translucent and have orange veins.

They are harmless insects; they neither bite nor sting. They are not venomous, and there is no evidence that they transmit diseases. They generally do not pose a threat to vegetation, but young plants may be damaged by excessive feeding or egg laying. It is thus advised not to plant new trees or shrubs just before an emergence of the periodical cicadas. Mature plants usually do not suffer lasting damage even by a mass-emergence.

Broods
Periodical cicadas are grouped into 30 broods, based on the year they emerge. Broods are numbered using Roman numerals; broods I???XVII are the seventeen-year cicadas, while broods XVIII???XXX are the thirteen-year cicadas. Some broods are not known to exist, but they are retained in the numbering scheme for convenience. This scheme was put forth by C.L. Martlat in his classic study of 1907. Since then the actual number of broods has been recognized as 15 rather than 30.

Brood III (the Iowan Brood) last emerged in 1997; its next emergence will be in 2014. Brood IX emerged in 2003. Brood X (the Great Eastern Brood), a seventeen-year brood stretching from New York to North Carolina on the East Coast to Illinois and Michigan, emerged in May 2004. Brood X is the largest of the broods of the periodical cicadas; it will emerge again in 2021.

The most recent brood to emerge is Brood XIII???the Northern Illinois Brood. After a seventeen-year hiatus, this brood emerged in 2007, in northern Illinois and in parts of Iowa, Wisconsin, Michigan and Indiana. Sightings in northern Illinois occurred as early as May 2006.

The next thirteen-year brood to emerge will be Brood XIX (the Great Southern Brood) in 2011 from the Midwest to Maryland and Virginia. Brood XXIII (the Lower Mississippi River Valley Brood) is another thirteen-year brood; it last emerged in 2002 and will re-emerge in 2015.

Brood VII is an isolated population in upstate New York and consists only of M. septendecim. It emerged in 2001, and hence its next emergence will be in 2018.

Life cycle
The nymphs of the periodic cicadas live underground, at depths of 30 cm (one foot) or more, feeding on the juices of plant roots. They stay immobile and go through five development stages before constructing an exit tunnel in the spring of their 13th or 17th year. These exit tunnels have a diameter of about 1???1.5 cm (½ in.)

The nymphs emerge at an evening when the soil temperature is above 17°C (63 F) and climb to a suitable place on the nearby vegetation to complete their transformation into an adult cicada. They molt one last time and then spend about six days in the leaves waiting for their exoskeleton to harden completely. Just after this final molt, the teneral adults are white, but darken within an hour.

The nymphs emerge in large numbers at about the same time, sometimes more than 1.5 million individuals per acre (>370/m²). Their mass-emergence is a survival trait called "predator satiation": for the first week after emergence, the periodic cicadas are an easy prey for reptiles, birds, squirrels, cats, and other small and large mammals. The cicadas' survival mechanism is simply to overwhelm predators by their sheer numbers, ensuring the survival of most of the individuals and thus of the species. It has been hypothesized that the emergence period of large prime numbers (13 and 17 years) is also a predatory avoidance strategy adopted to eliminate the possibility of potential predators receiving periodic population boosts by synchronizing their own generations to divisors of the cicada emergence period.

Adult periodical cicadas live only for a few weeks???by mid-July, they will all be gone. Their short adult life has one sole purpose: reproduction. The males "sing" a mating song; like other cicadas, they produce loud sounds using their tymbales. Receptive females respond to the calls of conspecific males with timed wing-flicks, which attract the males for mating. The sounds of a "chorus"???a group of males???can be deafening and reach 100 dB.

After mating, the male weakens and dies. The female lives a little longer in order to lay eggs: it makes between six and 20 V-shaped slits in the bark of young twigs and deposits up to 600 eggs there. Shortly afterwards, the female also dies. After about six to ten weeks, the eggs hatch and the newborn nymphs drop to the ground, where they burrow and begin another 13 or 17-year cycle. The carcasses of periodic cicadas decompose on the ground, providing a resource pulse of nutrients to the forest community.

http://en.wikipedia.org/wiki/Magicicada

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