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What is Brood X? When do cicadas come out in 2021? Answering your buggiest questions.

The Washington Post logo The Washington Post 4/1/2021 Bonnie Berkowitz, Artur Galocha

Billions of cicadas that have been underground since 2004 have begun to emerge en masse and will blanket parts of the eastern United States with their song and, eventually, their carcasses.

If you’re in the right location, ignoring them will be impossible.

diagram © Provided by The Washington Post What do you want to know about Brood X cicadas? Ask The Post. (May 6 | 1 p.m. EDT)

Where will the cicadas emerge in 2021?

If you live in the D.C. area, lucky you! You’re in the middle of cicada-Palooza, which has huge concentrations of Brood X cicadas.

People in other affected cities, such as Cincinnati and Philadelphia, will experience the insects as well, but New Yorkers may not. The last New York population, on Long Island, was nearly extinct in 2004. The sandy soil was never a good fit for cicadas, said John R. Cooley, who leads the Periodical Cicada Project at the University of Connecticut.

map © Provided by The Washington Post

Researchers at Mount St. Joseph University in Ohio hope to map this year’s crop, and they have created a cellphone app so people can document cicada sightings where they live.

What is Brood X?

These cicadas are not the usual green ones that show up in some parts of the country every year.

a insect on a branch: A Brood X cicada waits for its wings to dry after its emergence May 11, 2004, in Silver Spring, Md. © James M. Thresher/The Washington Post A Brood X cicada waits for its wings to dry after its emergence May 11, 2004, in Silver Spring, Md.

Brood X — pronounced “Brood 10,” because cicada broods are labeled with Roman numerals — is one of the largest of 15 broods of periodical cicadas in the United States. (Three broods come out every 13 years and 12 come out every 17 years.) Three species make up Brood X, and they are known for their fire-engine-red eyes, their loud choruses and their dramatic emergence every 17 years.


This year’s crop hatched in small tree branches in 2004 as as tiny, translucent nymphs, each about the size of a grain of rice. They dropped to the ground and burrowed below, sucking liquid from plant roots, and molting and growing.

After 17 years, the much larger nymphs crawl out of dime-size holes in the ground. They immediately climb a vertical surface, where they will molt one last time, breaking out of their brown exoskeletons as soft, white adults.

map © Provided by The Washington Post

The largest are more than an inch long. Within hours, they have full color, and a few days later, they are able to fly.

Adults cicadas live aboveground for two to four weeks and spend nearly all their time eating and trying to mate.

diagram © Provided by The Washington Post

When do the cicadas come out in 2021?

Brood X rummages around below ground, waiting for soil temperatures a foot or so below the surface to reach 64 degrees. The D.C. area’s up-and-down recent temperatures have caused some pockets to begin to emerge while others await a warmer spell.

Typically, most wait for a humid (but not stormy) evening to pop out of the tunnels they’ve been building for weeks.

Brood awakening: Cicadas emerging across D.C. area diagram © Provided by The Washington Post

How do cicadas make noise?

In Brood X, only the males can sing. They produce sound with membranes called tymbals, and their hollow abdomens amplify the call, but some of the details are still a mystery.

Each of the three species has a different set of calls.

diagram © Provided by The Washington Post

When a bunch of Brood X men get together, their chorus can reach 105 decibels — louder than a lawn mower. They may call to find others of their species, or to sound an alarm, but mostly they are trying to attract females.

Live like a cicada. Enter and exit singing.

Why do Brood X cicadas all come out at once?

Every species has a survival strategy. Some have killer claws or jaws, some have camouflage, some taste bad or spew poison.

Brood X cicadas, however, are lovers, not fighters, and those red eyes aren’t fooling anyone. Also, they are tasty to pretty much everything, including dogs, birds, reptiles and even some people.

Their superpower lies in vast numbers. Scientists call it the predator-satiation defense.

It means they simply “overwhelm the predators by filling their bellies, and there’s still enough left over to perpetuate the species,” said Michael Raupp, an entomologist at the University of Maryland. There just aren’t enough predators to swallow them all before they reproduce.

Cicadas have an elaborate courtship ritual that, if a female deems a male worthy, ends in mating. Usually within an hour afterward, the female will search for a tender tree branch, slice into it with her swordlike ovipositor, and lay eggs in the space.

diagram © Provided by The Washington Post

Six to 10 weeks later, tiny nymphs will hatch, drop to the ground, burrow below it and wait 17 years for their brief time in the sun.

Alexandra Petri: Are you a Brood X cicada or someone just emerging from pandemic isolation?

What do cicadas eat?

Cicadas get all their nutrients from tree xylem, a very watery sap that contains minerals and amino acids.

Fun fact: Few creatures we call “bugs” are actually classified as bugs by scientists, but cicadas are true bugs because of the way they eat. They suck food through strawlike beaks called rostrums.

diagram © Provided by The Washington Post

While underground, cicada nymphs poke their beaks into the tender roots of grasses and trees. After they emerge, they use those beaks to tap tree branches. The xylem hydrates and cools them in addition to providing nutrients.

All that liquid needs somewhere to go, however, so if you plan to spend a lot of time under cicada-filled trees, you may want to wear a hat to keep “cicada rain” off your head.

Do cicadas bite or sting?

Cicadas don’t bite, don’t have stingers and are not at all interested in people.

That said, every once in a while someone will claim to have been jabbed by a cicada. While this is extremely unlikely, Cooley said, it could happen in one of two ways — with the beak or the ovipositor. Either would mean the cicada has mistaken a human for a tree.

diagram © Provided by The Washington Post

“They live in a world where the surface that they live on is made of food, right? So they’ll always just stop and try to feed,” Cooley said.

But cicadas can’t easily break through human skin, and you would have plenty of time to shoo the bug away if you felt one trying.

“When they’re piercing bark to feed, they have to move their mouth parts to drill through the bark,” he said. “And when they’re piercing bark to lay the eggs, they have to move their ovipositor valves to do that. It’s not a fast process. It’s not like a bee sting or something where they come in and nail you.”

Cooley and Raupp both said they have handled thousands of cicadas and have never been jabbed.

Will the cicadas wreck my plants?

Almost never. Because cicadas don’t eat plants, your flowers and vegetables are safe, but you may want to take some precautions with very delicate trees.

Female cicadas make slits and lay eggs in small tree branches, preferring stems that are about 1/4- to 1/2-inch in diameter. Most established trees weather the process just fine.

However, some branch tips will wither and die back. This poses a risk to young trees only; for others, the damage is cosmetic. The process works as a natural pruning in forests, but you may not want cicadas to help prune your favorite ornamental cherry.

Many veteran gardeners will cover young or prized ornamental trees with netting to keep cicadas off them.

For much more on this topic, including tips for protecting your plants, see this story by Post gardening columnist Adrian Higgins.

The cicadas are coming, but gardeners need not panic

Can I compost cicadas?

Yes, cicada shells and bodies can contribute to a healthy compost mix, according to the U.S. Environmental Protection Agency.

The shells that the nymphs shed and leave all over the place at the beginning are made of chitin, just like lobster and crab shells, and count as “green” material in composting lingo. Fresh cicada carcasses that will litter the ground a few weeks later are stinky but also very rich in nitrogen, and they are considered “green” as well.

However, as cicada carcasses or shells age and dry out, both become more like a carbon-based brown, so consider that when calculating your compost balance.

What’s the difference between a cicada and a locust?

Locusts are an insatiable type of swarming grasshopper that can decimate food crops. Cicadas, on the other hand, belong to a completely different insect order, don’t have powerful jumping legs, and don’t even have the right mouth parts to devour crops.

diagram, schematic © Provided by The Washington Post

So why do people mix them up?

The confusion appears to date to the first settlers in Plymouth Colony, who got a heck of a surprise when millions of periodical cicadas suddenly emerged one spring in either 1631 or 1634.

According to a 2001 article in American Entomology that quotes several early manuscripts, it seems that the English settlers had no idea what was happening — periodical cicadas are unique to North America — but they knew the story of biblical plagues, saw the large bugs covering the trees and called them locusts. The name stuck long after scholars determined that cicadas and locusts are unrelated.

Graphics editing by Lauren Tierney

About this story

Map data sourced from the University of Connecticut. Tymbal information referenced from “What the buzz was all about: it song muscles rattle the tymbals of male periodical cicadas,” by Patrick C. Nahirney, et al. Emergence timeline data sourced from Cicada Mania. Cicada and locust size information from the Iowa State University’s entomology department.


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