All about Periodical Cicadas
by AMNH on
Quiet for months during the winter and early spring, the world of invertebrates—including insects—is bursting to life as the weather warms. But this year, as you’ve probably heard, brings a rare…treat: billions of cicadas, all along the Eastern seaboard, including New York.
As soon as the soil reliably warms to 64 degrees, nymphs of insects called periodical cicadas will emerge, after living underground for the past 17 years. By emerging en masse—some say there may be as many as 1 million cicadas per acre—these so-called Brood II cicadas are more likely to overwhelm predators, including other insects, birds, small mammals, turtles, and frogs, thus helping to ensure species survival.
Having fed on the xylem fluid found in the roots of deciduous trees all those years, three species of cicada will make up the brood. Each species has distinct behavior and song, but all are less than two inches long as adults, have black bodies with orange-red wing veins, and bright red eyes.
The holes they make when leaving the ground are about 3/8 inch to 1/2 inch in diameter, explains Museum entomologist Lou Sorkin. With forelegs adapted to digging, the nymphs dig until they are near the soil surface, where they create chambers and wait until the right moment to emerge, usually at night after a rain. Once out, they “quickly try to climb a vertical surface—a tree, a fencepost…your leg,” says Sorkin.
All in good time, the nymphs molt—the skin opens down the back; the adult cicada climbs out and soon unfurls its wings. (You can look for empty, shed skins of these “fifth-instar” nymphs hanging on leaves, tree trunks, and fenceposts.)
After four to six days, the cicadas are mature adults, with hardened bodies and stiff wings, and, in males, special membranes called tymbals that enable them to create songs to draw in females. And that’s the reason they’ve emerged for just these few short weeks: to mate. Up in the trees, during the day, you’ll start to hear a chorus of many thousands of wailing males calling out to females, who click in response.
Having mated, the females will later lay eggs using special organs called ovipositors to cut niches in tree-twigs in which to place the eggs. Those eggs, says Sorkin, will hatch about 6 to 10 weeks later.
The small nymphs that hatch will use their forelegs to burrow down into the soil, just as their mothers and fathers once did. In the soil, they’ll find tree roots to feed on, growing slowly to the fifth-instar nymph stage. In 17 years—in the year 2030—they’ll repeat the cycle again.
There will be another chance to see a different group of cicadas later this summer. The annual green-winged cicadas, which emerge in the hottest “dog days” of July through September in New York, are slightly larger than the periodical cicadas. They grow for about three to five years underground before emerging to mate.
To report your local sightings of cicadas or other invertebrates around greater New York City, visit the Museum’s iNaturalist project, New York is Wild!