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

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you spent the last 17 years of your life

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walking,

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eating,

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and sleeping

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above a dormant army of insects.

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These are the cicadas.

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Every 17 years,

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billions of them emerge from the ground

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to do three things:

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molt,

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mate,

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and die.

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There are fifteen different broods of cicadas out there,

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grouped by when they'll emerge from the ground.

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

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others are on a 17-year clock.

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Either way, the cicadas live underground

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for most of their lives,

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feeding on the juices of plant roots.

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When it's time to emerge,

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the adults will begin to burrow their way

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out of the ground

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and up to the surface,

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where they will live for just a few weeks.

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During these weeks, though,

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everybody will know the cicadas have arrived.

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There will be billions of them,

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and they're loud.

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Male cicadas band together

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to call for female mates,

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and their collective chorus can reach

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up to 100 decibels,

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as loud as a chain saw.

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

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or a lawn mower,

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male cicadas will flock to you,

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thinking that you're one of them.

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Now, like most things in nature,

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the cicadas don't arrive without a posse.

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There are all sort of awesome and gross predators and parasites

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that come along with the buzzing bugs.

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Take the fungus massospora for example.

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This little white fungus buries itself

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

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leaving behind its spores.

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When those spores rupture,

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they burst out of the still-alive cicada,

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turning the bug into a flying salt shaker of death,

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raining spores down upon

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its unsuspecting cicada neighbors.

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But while we know pretty precisely

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when the cicadas will arrive and fade away,

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we're still not totally certain of why.

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There are certain advantages

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

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The sheer number of cicadas coming out of the ground

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is so overwhelming to predators,

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it is essentially guaranteed

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that a few bugs will survive and reproduce.

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And since cicadas emerge every 13 or 17 years,

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longer than the lifespan of many of their predators,

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the animals that eat them

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don't learn to depend on their availability.

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But why 13 and 17 years

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instead of 16,

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or 18,

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or 12?

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Well, that part no one really knows.

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It's possible the number just happened by chance,

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or, perhaps, cicadas really love prime numbers.

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Eventually, the cicadas will mate and slowly die off,

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their call fading into the distance.

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The eggs that they lay will begin the cycle again,

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their cicada babies burrowing into the earth,

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feeding on plant juice,

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and waiting for their turn

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to darken the skies

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and fill the air with their songs.

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In 17 years, they'll be ready.

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Will you?