Where billions of cicadas will emerge this spring (and over the next decade), in one map

Mid-Atlantic cicadas will hear the call of spring. And then you’ll hear their mating calls, too.

For 17 years, cicadas do very little. They hang out in the ground, sucking sugar out of tree roots. Then, following this absurdly long hibernation, they emerge from the ground, sprout wings, make a ton of noise, have sex, and die within a few weeks. Then, their orphan progeny return to the ground and live the next 17 years in silence. Rarer are the 13-year cicadas, which do the same, but in a little more of a hurry — spending just 13 years underground.

Cicadas appear most years on the East Coast of the United States — sometimes ahead of schedule — but it’s a different 17- or 13-year crew that wakes up each time. (There are also, separately, some annual cicadas that emerge every year.)

This year, though, will be a rare event. Two groups — known as “broods” — are waking up during the same season. There will likely be billions, if not trillions, of the insects. According to NPR, the last time these two broods emerged at the same time was in 1803.

There’s the 17-year-group called Brood XIII, which is concentrated in Northern Illinois (brown on the map below), and the 13-year clutch, Brood XIX, which will emerge in Southern Illinois, Missouri, Arkansas, and throughout the Southeast (see them in light blue on the map below).

Emerging in these humongous annual batches is likely an evolutionary strategy. There are so many cicadas swarming around all at once that their predators, such as birds and small mammals, can’t make a meaningful dent in their numbers. As Vox’s Benji Jones explains:

their defense strategy is to flood the forests so that predators, from blue jays to squirrels (and, during these eruptions, everything in between), become so full that they literally can’t stomach another bite. That leaves plenty of insects to mate and lay eggs that will become the next generation of 17-year cicadas.

There are many mysteries about cicadas — what’s with the prime numbers on their alarm clocks, and for that matter, how the hell do they keep time? What is known is that when the ground temperatures reach around 64 degrees Fahrenheit, they’ll emerge this spring, numbering in the billions. And if you live in the Eastern half of the United States, it’s likely another brood, and another and another, wait patiently underground, all to emerge for you in the years ahead.