A cicada (a black insect with transparent wings and large red eyes) sits on a green leaf.
A 17-Year Cycle The emergence of periodic cicadas is one of nature’s great annual events, and it’s a boon to many other species of animals that feast on the slow-moving insects. © David Gumbart/TNC

Animals We Protect

What You Need to Know about Brood X Cicadas in 2021

They're here! It’s been 17 years since these cicadas went underground, so here's everything you need to know about their emergence.

All about Cicadas

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Do you recall hearing an inescapable screeching sound coming from nearly every tree and local forest in the spring of 2004? Did you notice winged insects clinging to unsuspecting people? Were you smacked in the head by one of these big bugs as they haphazardly flew around?

Your answer might be yes if you lived in certain areas of the US East Coast at the time. The sudden appearance of millions of screaming, red-eyed cicadas is not something that is easily forgotten.

Billions of Cicadas Emerge (2 MIN) TNC's Conservation Ecologist, Deborah Landau explains this amazing natural phenomenon happening every 17 years.

Periodical Cicada Emergence: May 2021

The periodical cicada spends the vast majority of its life underground, emerging after 13 or 17 years (depending on the species) to transform, reproduce and ultimately die over the space of just a few days. Huge populations of these insects have synced up to emerge within the same window of time to give them the best chance of successfully finding a mate and producing young before they are eaten by predators or expire naturally. These populations are called broods, and one of the largest—Brood X—started to emerge in mid May of 2021.

A newly emerged cicada dangles from the husk of its empty shell. It has a white body and translucent wings. Black markings on its face create the appearance of eyebrows over large red eyes
Waiting to Take Flight It takes a newly emerged cicada around 30 minutes for its new carapace to harden. © David Gumbart/TNC

Once the soil reached about 64 degrees Fahrenheit at a depth of 12-18 inches, the emergence of the cicadas was triggered. Male cicadas emerge first, followed by females a few days later. Females can be identified by their pointed abdomen and sheathed ovipositor, the organ they use to lay eggs. 

Once they leave the ground, the cicadas will shed their shells and develop wings, allowing them to fly around and locate fresh hardwood trees and shrubs. You can see the singing organ of the male cicada by gently raising its wing and looking for the tymbal located where the wing meets the body. Above ground, cicadas have no natural inclination to fly away from predators, which is why they don’t seem to be afraid of people.

After they've found a tree or shrub to land on, the cicadas will mate and lay eggs at the end of branches. Newly hatched cicadas will then chew through the branch tips, causing them to fall off, carrying the young insects back down to the soil where they will spend the next 17 years. Brood X will next emerge in 2038.

How Humans Impact Cicadas' Natural Cycles

This is one of nature’s great cyclical events, and it’s a boon to many other species of animals that feast on the slow-moving insects. Like so many other natural cycles though, factors like ongoing human development and climate change could have a significant impact on this year’s brood. Scientists are eager to see how many of the cicadas will make an appearance this year compared to previous generations.

There has been increasing evidence of cicadas emerging several years ahead of schedule, which some scientists have suggested may be due to shifting temperatures. At the same time, insect populations have also seen serious declines worldwide over the last few decades, but the causes of these drops are not yet fully understood.

You Can Help! Cicada Community Science

That makes it more important than ever for scientists to learn where cicadas are emerging and in what sort of numbers—and we can all help. Using phone apps like Cicada Safari and iNaturalist, you can make digital observations that use your phone’s GPS to populate a map, helping to determine if or how Brood X’s range may have shifted since they last appeared 17 years ago.

As loud as they may be, we have plenty of reasons to be happy that Brood X has shown up in huge numbers this year.

Three newly emerged cicadas in a line on a green leaf. Their soft white bodies dangle from empty brown shells while they wait for their carapace to harden.
Noisy Natural Wonder You can see the singing organ of the male cicada by gently raising its wing and looking for the tymbal located where the wing meets the body. © David Gumbart/TNC
× Three newly emerged cicadas in a line on a green leaf. Their soft white bodies dangle from empty brown shells while they wait for their carapace to harden.
Close view of a cicada as it emerges from its shell. It has a white body and small unformed yellow wings. Black markings appear to create eyebrows over beady red eyes.
Life Above Ground It takes a newly emerged cicada around 30 minutes to harden its new carapace and pump its wings full of blood. © David Gumbart/TNC
× Close view of a cicada as it emerges from its shell. It has a white body and small unformed yellow wings. Black markings appear to create eyebrows over beady red eyes.
Noisy Natural Wonder You can see the singing organ of the male cicada by gently raising its wing and looking for the tymbal located where the wing meets the body. © David Gumbart/TNC
Life Above Ground It takes a newly emerged cicada around 30 minutes to harden its new carapace and pump its wings full of blood. © David Gumbart/TNC

Living with Cicadas: Embrace the Emergence

With cicadas all around, you might be wondering how they will affect your pets, plants or yard. The good news is that cicadas are harmless on all counts.

Any damage that may be caused to mature trees and shrubs by hatching larvae should be minor and temporary. However, it’s probably a good idea to delay planting new trees until the fall.

If you’re worried about damage to an ornamental shrub or fruit producing tree, the best course of action is to cover it with netting while the cicadas are out (net holes should be 1 cm or smaller.) Be sure to attach the netting to the trunk or the cicadas will climb up the trunk to the branches. Spraying the tree with chemicals won’t stop the cicadas but may poison the animals that eventually eat them.

You may notice patches of your yard where chunks of sod have been removed and small holes have been dug. You are probably looking at evidence of foxes, raccoons, skunks and crows on the hunt for cicada nymphs and a high-protein snack.

A cicada sits on a blade of green grass. The insect has a black body, large red eyes, and long translucent wings with thick yellow veins.
Periodical Cicadas Cicadas do not eat garden plants. In fact, cicadas don’t really eat at all, but will use their mouthparts to sip sap from trees and stay hydrated. © David Gumbart/TNC

A Blast from the Past: 2004

It’s been 17 years since the last emergence of Brood X. What was happening in 2004?

  • Lord of the Rings won Best Picture at the Oscars
  • Swimmer Michael Phelps won 6 medals at the summer games in Athens
  • George W. Bush was serving his 4th year in office
  • The final episode of Friends aired on May 6, 2004
  • Facebook was founded
  • The Boston Red Sox won their first World Series since 1918
  • Children born in 2004 may now be getting ready to graduate from high school