Trillions of red-eyed periodical cicadas that have pumps in their heads and jet-like muscles in their rears are about to emerge in the eastern United States in numbers not seen in decades and possibly centuries.
Crawling out from underground every 13 or 17 years, with a collective song as loud as jet engines, the periodical cicadas are nature's kings of the calendar.
These black bugs with bulging eyes differ from their greener-tinged cousins that come out annually. They stay buried year after year, until they surface and take over a landscape, covering houses with shed exoskeletons and making the ground crunchy.
The largest geographic brood in the nation — called Brood XIX and coming out every 13 years — has begun emerging in Georgia and is about to march through the Southeast. It's a sure sign of the coming cicada occupation. They emerge when the ground warms to 64 degrees, which is happening earlier than it used to because of climate change, entomologists said. The bugs are brown at first but darken as they mature.
The unusual cicada double invades a couple parts of the United States in what University of Connecticut cicada expert John Cooley called "cicada-geddon." The last time these two broods came out together in 1803 Thomas Jefferson, who wrote about cicadas in his Garden Book but mistakenly called them locusts, was president.
"Periodic cicadas don't do subtle," Cooley said.
If you're fascinated by the upcoming solar eclipse, the cicadas are weirder and bigger, said Georgia Tech biophysicist Saad Bhamla.
"We've got trillions of these amazing living organisms come out of the Earth, climb up on trees and it's just a unique experience, a sight to behold," Bhamla said. "It's like an entire alien species living underneath our feet and then some prime number years they come out to say hello."
At times mistaken for voracious and unrelated locusts, periodical cicadas are more annoying rather than causing biblical economic damage. They can hurt young trees and some fruit crops, but it's not widespread and can be prevented.
Soon after the insects appear in large numbers in Georgia and the rest of the Southeast, cicada cousins that come out every 17 years will inundate Illinois. They are Brood XIII.
"You've got one very widely distributed brood in Brood XIX, but you have a very dense historically abundant brood in the Midwest, your Brood XIII," said University of Maryland entomologist Mike Raupp.
"And when you put those two together… you would have more than anywhere else any other time," University of Maryland entomologist Paula Shrewsbury said.
These hideaway cicadas are found only in the eastern United States and a few tiny other places. There are 15 different broods that come out every few years, on 17- and 13-year cycles. These two broods may actually overlap — but probably not interbreed — in a small area near central Illinois, entomologists said.
The numbers that will come out this year — averaging around 1 million per acre over hundreds of millions of acres across 16 states — are mind-boggling. Easily hundreds of trillions, maybe quadrillions, Cooley said.
The origin of some of the astronomical cicada numbers can likely be traced to evolution, Cooley and several other entomologists said. Fat, slow and tasty, periodical cicadas make ideal meals for birds, said Raupp. But there are too many for them to be eaten to extinction, he said.
"Birds everywhere will feast. Their bellies will be full and once again the cicadas will emerge triumphant," Raupp said.
The other way cicadas use numbers, or math, is in their cycles. They stay underground either 13 or 17 years, both prime numbers. Those big and odd numbers are likely an evolutionary trick to keep predators from relying on a predictable emergence.