A Time article about the upcoming emergence of Brood X cicadas in the U.S. has the following quote from a biologist:
“It’s not something you can ignore,” says John Cooley, a biologist at the University of Connecticut. “When they come out it’ll be millions per acre.”
I found another article about the Brood X cicadas with this quote from a professor:
“Oh, it’s deafening,” said Matt Kasson, an associate professor of plant pathology and mycology at West Virginia University. [...] “You'll get tens of millions emerging per acre,” Kasson said.
Cicadas are 1-2 inches long, so let's say the average cicada is 1.5 inches long. Based on photos, their width is about one-third of their length, so let's say the average cicada is 0.5 inches wide. That means the average cicada would take up an area of about 0.75 square inches.
Since one acre is equivalent to 6,272,640 square inches, about 8,363,520 cicadas could fit in one acre if they were all side by side next to each other. So if there were millions of cicadas per acre, the ground would practically be covered with them if they were all sitting on the ground. If there were tens of millions of cicadas per acre, there would be multiple layers of them completely covering the ground.
Of course, when the cicadas emerge, they won't all be sitting on the ground - they'll spend a lot of time at various heights in trees. But still, I am skeptical of the claims that there will be millions or tens of millions of them per acre. Is that really true?