TAKOMA PARK, MD - MAY 10: The empty shell of a periodical cicada nymph clings to a tree after the adult insect molted on May 10, 2021 in Takoma Park, Maryland. Once soil temperatures reach about 64°F, billions and billions of these periodical cicadas -- members of Brood X -- will emerge in fifteen states and the District of Columbia after living underground for 17 years. The cicadas will emerge, molt, mate, lay eggs and die within a matter of weeks.  (Photo by Chip Somodevilla/Getty Images)

In pictures: Brood X cicadas emerge after 17 years underground

The story of the Brood X cicadas, emerging after 17 years.

Every 17 years, members of a group of periodical cicadas (known as Brood X) start to emerge from their underground hiding-places, shedding their skins on trees and turning into adults.

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Billions and billions of these cicadas from 15 US states start to come to the surface when the soil above them hits a temperature of 17.7ºC.

Within a matter of weeks, these cicadas will emerge, grow into adults, breed, lay eggs and die, and won’t be seen again for another 17 years.

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Counting down the days

COLLEGE PARK, MD - MAY 03: Colette Lord, 20, an ecology and evolution student at the University of Maryland, measures the soil temperature in a wooded area on campus on May 03, 2021 in College Park, Maryland. The soil measured 58 degrees, six degrees cooler than necessary for the periodical cicadas from Brood X to emerge. Lord is part of a 15 students who are measuring and monitoring the area for the rise of billions of the airborne insects who have been eating and growing under ground for 17 years. (Photo by Chip Somodevilla/Getty Images)
Colette Lord, 20, an ecology and evolution student at the University of Maryland, measures the soil temperature in a wooded area on campus on 3 May 2021 in College Park, Maryland, USA. The soil measured 14.4 degrees celsius, slightly cooler than necessary for the periodical cicadas from Brood X to emerge. Lord is part of a group of 15 students who are measuring and monitoring the area for the rise of billions of the airborne insects that have been eating and growing under ground for 17 years. Photo by Chip Somodevilla/Getty Images

Emergence

TAKOMA PARK, MD - MAY 10: A periodical cicada begins to molt from its nymph state on May 10, 2021 in Takoma Park, Maryland. Once soil temperatures reach about 64°F, billions and billions of periodical cicadas -- members of Brood X -- will emerge in fifteen states and the District of Columbia after living underground for 17 years to molt, mate and die within a matter of weeks. (Photo by Chip Somodevilla/Getty Images)
A periodical cicada begins to moult from its nymph state on 10 May 2021 in Takoma Park, Maryland, USA. Photo by Chip Somodevilla/Getty Images

Shed this skin

Mandatory Credit: Photo by Carolyn Kaster/AP/Shutterstock (11889562a) An adult cicada sheds its nymphal skin on the bark on an oak tree, on the University of Maryland campus in College Park, Md. Trillions of cicadas are about to emerge from 15 states in the U.S. East. Scientists say Brood X is one of the biggest for these bugs which come out only once every 17 years Cicada Invasion, College Park, United States - 04 May 2021
An adult cicada sheds its nymphal skin on the bark on an oak tree, on 4 May 2021 at the University of Maryland campus in College Park, USA. Photo by Carolyn Kaster/AP/Shutterstock

An empty shell

TAKOMA PARK, MD - MAY 10: The empty shell of a periodical cicada nymph clings to a tree after the adult insect molted on May 10, 2021 in Takoma Park, Maryland. Once soil temperatures reach about 64°F, billions and billions of these periodical cicadas -- members of Brood X -- will emerge in fifteen states and the District of Columbia after living underground for 17 years. The cicadas will emerge, molt, mate, lay eggs and die within a matter of weeks. (Photo by Chip Somodevilla/Getty Images)
The empty shell of a periodical cicada nymph clings to a tree after the adult insect moulted on 10 May 2021 in Takoma Park, Maryland, USA. Photo by Chip Somodevilla/Getty Images

Ready to fly

Mandatory Credit: Photo by Carol Guzy/ZUMA Wire/Shutterstock (11897682c) Brood X 17-year Cicadas emerge in Fairfax VA on May 10, 2021. Cicada, Fairfax, VA, USA - 10 May 2021
A Brood X 17-year cicada photographed in Fairfax, Virginia, USA, on 10 May 2021.
Photo by Carol Guzy/ZUMA Wire/Shutterstock

Inside the empty shell

TAKOMA PARK, MD - MAY 10: The empty shell of a periodical cicada nymph clings to a tree after the adult insect molted on May 10, 2021 in Takoma Park, Maryland. Once soil temperatures reach about 64°F, billions and billions of these periodical cicadas -- members of Brood X -- will emerge in fifteen states and the District of Columbia after living underground for 17 years. The cicadas will emerge, molt, mate, lay eggs and die within a matter of weeks. (Photo by Chip Somodevilla/Getty Images)
The empty shell of a periodical cicada nymph clings to a tree after the adult insect moulted on 10 May 2021 in Takoma Park, Maryland, USA. Photo by Chip Somodevilla/Getty Images

Clinging on

The empty shell of a periodical cicada nymph clings to a tree after the adult insect molted on May 10, 2021 in Takoma Park, Maryland. Once soil temperatures reach about 64°F, billions and billions of these periodical cicadas -- members of Brood X -- will emerge in fifteen states and the District of Columbia after living underground for 17 years. The cicadas will emerge, molt, mate, lay eggs and die within a matter of weeks. (Photo by Chip Somodevilla/Getty Images)
The empty shell of a periodical cicada nymph clings to a tree after the adult insect moulted on 10 May 2021 in Takoma Park, Maryland, USA. Photo by Chip Somodevilla/Getty Images

Preparing for the wave

In anticipation of the emergence of billions of periodical cicadas, this young tree is wrapped in netting to prevent the insects from depositing eggs in the small branches on May 10, 2021 in Takoma Park, Maryland. Once soil temperatures reach about 64°F, billions and billions of periodical cicadas -- members of Brood X -- will emerge in fifteen states and the District of Columbia after living underground for 17 years to molt, mate and die within a matter of weeks. (Photo by Chip Somodevilla/Getty Images)
In anticipation of the emergence of billions of periodical cicadas, this young tree is wrapped in netting to prevent the insects from depositing eggs in the small branches on 10 May 2021 in Takoma Park, Maryland, USA. Photo by Chip Somodevilla/Getty Images

Branching Out

A periodical cicada nymph clings to a tree branch on May 11, 2021 in Greenbelt, Maryland. - Some are waiting for their arrival with trepidation, others are curious what they might taste like: Americans are swapping tips on how best to weather the storm when billions of cicadas soon emerge after 17 years underground. (Photo by JIM WATSON / AFP) (Photo by JIM WATSON/AFP via Getty Images)
A periodical cicada nymph clings to a tree branch on 11 May 2021 in Greenbelt, Maryland, USA. Some are waiting for their arrival with trepidation, others are curious what they might taste like. Americans are swapping tips on how best to weather the storm when billions of cicadas soon emerge. Photo by Jim Watson/AFP/Getty Images

Spot the cicada

BLOOMINGTON, INDIANA, UNITED STATES - 2021/05/14: A woman looks at a Brood X cicada which has emerged from the ground along First Street on Vinegar Hill in Bloomington, Indiana. Billions of cicadas are expected to emerge this year in Indiana and several other states after living in the ground for 17 years. (Photo by Jeremy Hogan/SOPA Images/LightRocket via Getty Images)
A woman looks at a Brood X cicada which has emerged from the ground along First Street on Vinegar Hill in Bloomington, Indiana, USA, 14 May 2021. Photo by Jeremy Hogan/SOPA Images/LightRocket/Getty Images

Coming out of the ground

BLOOMINGTON, INDIANA, UNITED STATES - 2021/05/14: Brood X cicadas emerge from the ground along First Street on Vinegar Hill in Bloomington, Indiana. Billions of cicadas are expected to emerge this year in Indiana and several other states after living in the ground for 17 years. (Photo by Jeremy Hogan/SOPA Images/LightRocket via Getty Images)
Brood X cicadas emerge from the ground along First Street on Vinegar Hill in Bloomington, Indiana, USA, 15 May 2021
Photo by Jeremy Hogan/SOPA Images/LightRocket/Getty Images

More empty shells

A Magicicada periodical cicada is seen in the middle of empty cicadas shells, displayed by a child on the ground, on May 16, 2021 in Arlington, Virginia. - Some are waiting for their arrival with trepidation, others are curious what they might taste like: Americans are swapping tips on how best to weather the storm when billions of cicadas soon emerge after 17 years underground.Before invading parks and people's gardens, the insects have already conquered the airwaves, social media and newspapers, especially in parts of the eastern, central and southern United States where
A  periodical cicada is seen in the middle of empty cicadas shells, displayed by a child on the ground, on 16 May 2021 in Arlington, Virginia, USA. Before invading parks and people’s gardens, the insects have already conquered the airwaves, social media and newspapers, especially in parts of the eastern, central and southern United States where “Brood X” is due to emerge. Photo by Olivier Douliery/AFP/Getty Images

Visiting the Capitol

UNITED STATES - MAY 16: The empty shell of a cicada clings to the side of a tree at the U.S. Capitol in Washington on Sunday morning, May 16, 2021. Billions of Brood X cicadas have begun to emerge after living underground for 17 years. (Photo by Bill Clark/CQ-Roll Call, Inc via Getty Images)
The empty shell of a cicada clings to the side of a tree at the US Capitol in Washington DC, USA, on Sunday morning, 16 May 2021. Photo by Bill Clark/CQ-Roll Call, Inc/Getty Images