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  • If you live on the east coast of the United States,

  • you spent the last 17 years of your life

  • walking,

  • eating,

  • and sleeping

  • above a dormant army of insects.

  • These are the cicadas.

  • Every 17 years,

  • billions of them emerge from the ground

  • to do three things:

  • molt,

  • mate,

  • and die.

  • There are fifteen different broods of cicadas out there,

  • grouped by when they'll emerge from the ground.

  • Some of these broods are on a 13-year cycle,

  • others are on a 17-year clock.

  • Either way, the cicadas live underground

  • for most of their lives,

  • feeding on the juices of plant roots.

  • When it's time to emerge,

  • the adults will begin to burrow their way

  • out of the ground

  • and up to the surface,

  • where they will live for just a few weeks.

  • During these weeks, though,

  • everybody will know the cicadas have arrived.

  • There will be billions of them,

  • and they're loud.

  • Male cicadas band together

  • to call for female mates,

  • and their collective chorus can reach

  • up to 100 decibels,

  • as loud as a chain saw.

  • In fact, if you happen to be using a chain saw

  • or a lawn mower,

  • male cicadas will flock to you,

  • thinking that you're one of them.

  • Now, like most things in nature,

  • the cicadas don't arrive without a posse.

  • There are all sort of awesome and gross predators and parasites

  • that come along with the buzzing bugs.

  • Take the fungus massospora for example.

  • This little white fungus buries itself

  • in the cicada's abdomen and eats the bug alive,

  • leaving behind its spores.

  • When those spores rupture,

  • they burst out of the still-alive cicada,

  • turning the bug into a flying salt shaker of death,

  • raining spores down upon

  • its unsuspecting cicada neighbors.

  • But while we know pretty precisely

  • when the cicadas will arrive and fade away,

  • we're still not totally certain of why.

  • There are certain advantages

  • to having your entire species emerge at once, of course.

  • The sheer number of cicadas coming out of the ground

  • is so overwhelming to predators,

  • it is essentially guaranteed

  • that a few bugs will survive and reproduce.

  • And since cicadas emerge every 13 or 17 years,

  • longer than the lifespan of many of their predators,

  • the animals that eat them

  • don't learn to depend on their availability.

  • But why 13 and 17 years

  • instead of 16,

  • or 18,

  • or 12?

  • Well, that part no one really knows.

  • It's possible the number just happened by chance,

  • or, perhaps, cicadas really love prime numbers.

  • Eventually, the cicadas will mate and slowly die off,

  • their call fading into the distance.

  • The eggs that they lay will begin the cycle again,

  • their cicada babies burrowing into the earth,

  • feeding on plant juice,

  • and waiting for their turn

  • to darken the skies

  • and fill the air with their songs.

  • In 17 years, they'll be ready.

  • Will you?

If you live on the east coast of the United States,

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B2 TED-Ed emerge dormant fungus ground bug

【TED-Ed】Cicadas: The dormant army beneath your feet - Rose Eveleth

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    Sara Wang posted on 2013/11/13
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