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W : 22 May 2007 • 9:03AM -0400

[WritersMailbox] FAQ: Cicada Facts: Understanding the Invasion
by Bill Holmes


Cicada Facts: Understanding the Invasion
National Geographic News
Updated May 21, 2007

The billions of periodical cicadas of Brood XIII are expected to
launch their invasion of northern Illinois and parts of Iowa,
Wisconsin, Michigan, and Indiana this week (United States map).

Cicadas—insects that spend most of their lives as nymphs, burrowed
underground and sucking sap from tree roots—emerge once every 17
years. Living fast and dying young, the shrimp-size, red-eyed insects
transform into adults, reproduce, and die, all the while buzzing to
beat the band.

• Cicadas are often called locusts, but locusts are migratory
grasshoppers that often travel in vast swarms. The appearance of
cicadas in large numbers apparently caused the early European settlers
in North America to equate them with the plague of locusts mentioned
in the Bible.

• Periodical cicadas are found only in the United States east of the
Great Plains. Seventeen-year cicadas are found mainly in the northern,
eastern, and western part of their range. Thirteen-year cicadas
predominate in the South. Within the 17-year cicadas there are 12
year-classes or broods.

• While different broods emerge in different years, there are some
years in which there are no broods, the so-called empty-class years.
Broods generally are geographically based, but there can be some
overlapping. Some broods are found only in small areas. Others, like
Brood XIII, can range across many U.S. states.

• Each brood of 17-year cicadas actually consists of three different
species, and they all emerge together. The species look different from
one another, and each one has its own song. Listen carefully and you
should be able to distinguish the different choruses, according to
experts. The three songs have been described as sounding like the word
"pharaoh," a sizzling skillet, and a rotary lawn sprinkler. The
different species sing at different times of the day—one favors the
early part of the day, another prefers midday, and the third takes the
late-afternoon shift.

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