Trillions of a particular breed of periodical cicadas, called Brood X, are set to emerge having spent 17 years underground, a report by AP explains.
Over the coming days and weeks, swathes of the inch-long insects will emerge from underground throughout parts of 15 US states, including Indiana, Ohio, Pennsylvania, and Maryland.
As per a report by National Geographic, this natural phenomenon was first recorded in the late spring of 1634 by pilgrims in Massachusetts who thought they were witnessing biblical swarms of pestilential locusts emerging from the ground.
Today, we know that seven species of periodical cicadas exist and that they emerge every 13 or 17 years in North America. The cicadas are further distinguished by the group they migrate with, known as their brood, which is assigned a number with a Roman numeral.
Brood X nymphs emerge as soil temperatures rise in the spring
The 2021 periodical cicadas, known as Brood X, are the largest of the 15 known periodical cicada broods. As NASA points out, the cicadas typically emerge when the soil 8 inches below the ground reaches 64.5 F (approx. 18 degrees Celsius).
Brood X cicadas are coming! Researchers at @NASAGoddard are using computer models to forecast when soil temperatures might be favorable for the cicadas to emerge — just for local interest.https://t.co/iA8ohRL6JJ pic.twitter.com/Qny025UMxy— NASA Earth (@NASAEarth) May 3, 2021
The US space agency is utilizing its North American Land Data Assimilation System Phase 2 (NLDAS-2) to help keep the public advised.
Once temperatures are warm enough, the young cicadas, called nymphs, will emerge from their burrows below the ground, where they survive for the first 17 years of their lives by feeding on tree sap.
The Brood X cicadas emerge so rarely that, as FastCompany reports, smartphone tracking apps weren't really a thing when they last appeared in 2004. Now, insect expert Gene Kritsky has developed an app called Cicada Safari to help users map the emergence of the 2021 cicadas.
Though scientists are not sure why exactly periodical cicadas emerge every 13 to 17 years, some have theorized that the periods evolved over centuries as an optimal means to avoid predators.
Others suggest that, by emerging in years with prime numbers, the different cicada broods avoid emerging at the same time, meaning they won't exhaust their natural resources.
A sign of good times
Though some still mistake periodical cicadas for locusts and fear their emergence, the scientific community explains that their emergence is an important indicator that forests are in good health. When they die they actually help to fertilize the soil and move nutrients around the ecosystem.
As entomologist John Cooley of the University of Connecticut told AP, "when they come out, it’s a great sign that forests are in good shape. All is as it is supposed to be."
Though some still mistake periodical cicadas for locusts and fear their emergence, Jeffrey Lockwood, entomologist and professor of natural sciences and humanities at the University of Wyoming, told National Geographic that "it's a phenomenon that ought to generate awe and respect and wonder."
Lockwood said that the cicadas should be seen as a humbling symbol of a bygone era when humans formed a part of a much more diverse global ecosystem.
"We’ve done such a thorough job of decimating the natural world that any organism, at least any animal, that appears in these sorts of numbers—it’s wonderfully humbling," Lockwood explained.
If you want to know where exactly the Brood X cicadas will appear, the University of Connecticut has released two interactive maps showing the cicadas' expected locations based on past records.