A brood of trillions of periodical cicadas is poised to emerge in some states across the country this month. 

The insects, which last appeared above ground almost two decades ago, are known as "Brood X," the "Big Brood," or the Great Eastern Brood. 

CICADAS LIVING UNDERGROUND FOR PAST 17 YEARS TO EMERGE IN THESE STATES THIS SUMMER

Brood X has reportedly already made its 2021 debut in Southern states, and there have been reports of sightings in Georgia, Virginia, Maryland, New Jersey, Ohio and the District of Columbia.

University of Maryland entomologist Paula Shrewsbury displays a handful of cicada nymphs found in a shovel of dirt in a suburban backyard in Columbia, Md., Tuesday, April 13, 2021. This is not an invasion. The cicadas have been here the entire time, quietly feeding off tree roots underground, not asleep, just moving slowly waiting for their body clocks tell them it is time to come out and breed. They’ve been in America for millions of years, far longer than people. (AP Photo/Carolyn Kaster)

University of Maryland entomologist Paula Shrewsbury displays a handful of cicada nymphs found in a shovel of dirt in a suburban backyard in Columbia, Md., Tuesday, April 13, 2021. This is not an invasion. The cicadas have been here the entire time, quietly feeding off tree roots underground, not asleep, just moving slowly waiting for their body clocks tell them it is time to come out and breed. They’ve been in America for millions of years, far longer than people. (AP Photo/Carolyn Kaster)

Videos and photos posted to social media show the black, winged creatures with bright-red eyes on porches and in the grass. 

"Walking the dog after sunset. Thought wind was gently rustling leaves, except the noise was coming from my feet. #Cicadas are emerging," wrote George Mason University's Christina Tyler Wenks. "@capitalweather’s prediction was spot on. #broodx"

But, for many, the next few days mark the calm before the storm. 

As ground temperatures warm to 64 degrees, Delaware, West Virginia, North Carolina, Pennsylvania, New York, Michigan, Illinois, Indiana, Kentucky and Tennessee will all be visited by singing cicadas. 

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In recent years, ground temperatures have been warming to that temperature earlier due to climate change, The Associated Press reports.

There are six species of periodical cicada in the Eastern U.S., according to CNET and three species in Brood X.

A cicada nymph moves in the grass, Sunday, May 2, 2021, in Frederick, Md. (AP Photo/Carolyn Kaster)

A cicada nymph moves in the grass, Sunday, May 2, 2021, in Frederick, Md. (AP Photo/Carolyn Kaster)

A U.S. Forest Service map shows Brood X concentrations in Maryland, Delaware, Pennsylvania, Indiana, Ohio, and eastern Tennessee.

With as many as 1.5 million cicadas per acre, the adult brood is above ground to mate, emerging at dark in an attempt to avoid predators. Notably, their mating calls can reach up to 100 decibels.

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After their two-to-four-week excursion, the adult cicadas die following intercourse and cicada eggs are deposited in tree branches where the larvae or "nymphs" then hatch and burrow into the soil.

The next generation will surface in 2038.