But even with their enormous numbers, certain aspects of the cicadas’ subterranean phase are mysterious—and even divisive—for biologists. While the nymphs have forelimbs specifically modified to burrow like a mole’s, they can also maneuver through existing cracks and holes with their rice-grain-sized bodies. Some might even begin their journey by following the tunnels the previous generation made to crawl out of the ground. Once they’re an inch or two below the surface, the nymphs likely feed on grass roots, says Gene Kritsky, an entomologist at Mount St. Joseph University who’s written a book on Brood X. Cooley is less sure of that idea, however. “I don’t think we know a lot about what goes on down there,” he says. “If you had X-ray vision and could look at the soil, it would be a big mass of roots, and it would be nearly impossible for you or anybody else to tell what the roots went to.” Both Kritsky and Cooley agree, though, that the next step is for the nymphs to find deeper, more substantial roots to support their long journey to adulthood. But how low do they go? Older nymphs in their last underground stages of development can typically be found 4 to 6 inches from the surface, Kritsky says. But one cold November, he tracked them 8 to 12 inches down, which makes him think that the bugs were burrowing farther to reach warmer temperatures. Still, that depth is above the frost line in many places, Cooley notes, “which raises some interesting questions.” How do they avoid freezing? And how much do they really move between different layers and roots? “What we don’t know is how they remember what year has gone by,” Kritsky notes further. In the time being, folks in the mid-Atlantic states can check out the second act of the Brood X cicada show by placing a piece of black construction paper at the base of a tree where there’s evidence of egg laying. “You’ll see the little nymphs fall onto [the paper],” Cooley says, “and then find their way down into the soil and start the whole cycle over again.”
