You're in for a loud few weeks, Pennsylvania, Maryland, and Delaware.
closeup of a cicada on tree branch
Credit: Minh Hoang Cong / 500px / Getty

If you live in the United States—especially east of the Rocky Mountains—the drone of cicadas is as much a part of summertime as lemonade and sunburn. But, depending on which state you live in, you might notice that some years just seem louder than others.

You're not crazy. In addition to your run-of-the-mill, seasonal cicadas who show up every summer, many Midwest and eastern seaboard states are also home to broods of what are known as "periodical cicadas."

So if you find yourself yelling to be heard at your twilight picnic this summer in certain eastern states—Cicada Invasion 2021 might be why.

What Are Periodical Cicadas?

They're the groups of the insects whose larvae burrow deep into the ground and feed on tree and plant roots for periods ranging from 13 to 17 years. Once those gestation periods end, billions (some say even trillions) of the insects burst from the ground, make their familiar, droning mating call, and do what comes naturally.

There are 15 different broods across the eastern U.S., all with their own, staggered gestation period. This year marks the emergence of Brood X (that's "Brood 10," not "Ah! It's the Unknown Brood! Run!"), which first went into the ground the three years before iPhones were a thing. Their lifespans out in the light of day will be short—typically around five or six weeks—but while they're here, they will certainly make their presence known through their unmistakable, droning song; a buzzing sound that can reach over 100 decibels.

Once the mating call has done its job and the cicadas have fertilized their eggs, the now-17-year-old adults will die off en masse, and the newly hatched larvae will make their way back into the ground for another long, dark stay, and the process will repeat itself.

While they are here, despite being noisy, cicadas are largely considered a beneficial species. They feed almost exclusively on the sap of mature trees (often the same ones whose roots they fed on as babies), their burrows help to aerate the soil and, when they die, their husks provide nutrients to surrounding plant life. If you want, you can even eat them.

Cicadas are often confused with locusts, but the two are, in fact, distinctly separate species. Locusts have more in common with grasshoppers and are herbivores who can cause widespread damage to crops and plant life during their swarming "gregarious stage." And while cicada broods can often be very densely packed into a relatively small area—as many as 1.5 million in a single acre—they don't tend to migrate much at all. Plus, plants are safe from the harmless little sap suckers.

Where Will This Year's Cicadas Emerge?

So who draws the short straw this summer? If you live in Indiana, western Ohio, the eastern half of Pennsylvania, Maryland, and Delaware, congratulations! It's your turn. Same goes for smaller sections of eastern Tennessee, northern Georgia, northern Virginia, southern Michigan, eastern Illinois, and Long Island, N.Y.

According to The Washington Post, you can expect to start seeing these vocal bugs in May.

Overall, periodical cicadas—shown here in this map from the U.S. Department of Agriculture's Forest Service—territories stretch from New York to as far south as Louisiana and from the Atlantic seaboard to mid-Oklahoma. After Brood X finishes their cycle this year, we'll have only annual cicada populations until northern Illinois, southern Wisconsin, and eastern Iowa say hello to Brood XIII in 2024.