Periodical cicada
Credit: © Thinkstock

They’ve waited underground for 17 years. Now, they’re coming to the surface to burst out of their skins, give off earsplitting screeching sounds, bore into trees, and cover the ground with their carcasses. But—like many blockbusters over the past year and a half—you can’t view this spectacle in movie theaters. You can’t even stream it on Netflix. If you live in the eastern U.S. Midwest or Middle Atlantic, this summer’s invasion is coming to a backyard or forest preserve near you. It’s called Brood X.

Brood X is not a movie, but a group of cicadas emerging this month. A cicada is a large insect with four thin wings which it folds over its body like a peaked roof. It can measure 1 to 2 inches (2.5 to 5 centimeters) long. It has a wide head and short, bristlelike antennae (feelers).

Just as crickets serenade us on warm summer nights, cicadas make up the soundtrack of hot summer afternoons. The male cicada makes two drumlike membranes (thin sheaths of skin) on the abdomen vibrate rapidly. This produces a characteristic buzzing sound. The sound attracts females or calls large numbers of males together. Each species (kind) of cicada has its own song. Male cicadas often assemble in large groups and produce a loud chorus of sounds.

Many of us hear cicadas every summer. So why is this summer different? There are thousands of species of cicadas. They can be roughly divided into two types: annual cicadas and periodical cicadas. As their name suggests, annual cicadas can be heard every year. But periodical cicadas emerge on 13- or 17-year cycles. Brood X is a 17-year periodical cicada, having last emerged in 2004. Other brood numbers (X is the Roman numeral for 10) emerge in different years in different regions. But Brood X is one of the largest and most famous.

Why do periodical cicadas emerge this way? It has to do with evading predators. Cicadas are a hearty, protein-packed snack for birds, raccoons, foxes, opossums, fish, spiders, and practically any other animal. Humans eat them, too! Cicadas are vulnerable when they are emerging. They don’t bite or sting and are clumsy flyers. But when so many cicadas emerge at once, there are just too many for predators to eat. Even with every predator’s belly filled with cicadas, billions or trillions survive to reproduce.

Seventeen years is a long time. Potential predators can’t rely on a food source that appears so infrequently. So, although animals take advantage of the cicada smorgasbord, nothing has evolved to rely on them exclusively.

Where do periodical cicadas go for all those years? After the adults mate, the female bores into twigs of bushes and trees with a sawlike organ near the tip of her abdomen. She lays her eggs in the holes. The eggs hatch in a few weeks and the young cicadas, called nymphs, drop to the ground. They live in the soil and eat roots for years—17 years in the case of Brood X.

The periodical cicadas will spend the summer shedding their skins and making lots of noise. However you decide to spend your summer, have fun and keep an ear out for Brood X!