Naturalist Rick Koval was leading a hike in the Delaware Water Gap when he noticed what appeared to be carelessness. On one section of the trail, every rock was carelessly flipped over and rolled around. At first Koval suspected someone searching for snakes or salamanders had neglected return the rocks to their resting place.
But upon closer inspection, Koval saw that it was black bears that had been busy flipping over every rock.
And they had a good reason.
Underneath the rocks were fat, succulent cicada larva - a feast that wildlife like bears can enjoy once every 17 years.
One of the six species of periodical cicadas that are found in Pennsylvania are emerging in 17 counties this month. Three species emerge every 17 years while the other three surface every 13 years. The current invasion, which is Brood II, was last seen in 1996. They can be found in Berks, Bucks, Carbon, Chester, Dauphin, Delaware, Lancaster, Lebanon, Lehigh, Luzerne, Monroe, Montgomery, Northampton, Philadelphia, Pike, Schuylkill and Wyoming counties.
“We think of them as the Methuselah of the insect world,” said Gregory Hoover, senior extension associate in entomology.
“These insects are harmless to people, but they can cause some damage to shade trees, fruit trees and high-value woody ornamental plants.”
The cicada, which is often mistakenly referred to as a locust, is native to North America and isn’t found anywhere else in the world.
The last time Brood II saw the light of day, a gallon of gas cost $1.22, Bill Clinton was elected President and less than 10 million people had the internet.
Back then, Brood II began their lives as nymphs, hatching from eggs deposited under the bark of trees and dropping to the ground where the enter the soil, not to see the light of day for 17 years.
One would think that the insects would be relatively safe spending 17 years underground, but that’s not the case.
Koval believes the length of time between hatching as nymphs and emergence makes cicadas more susceptible.
“It’s an idle time during which a lot of changes can happen to their habitat above, such as deforestation,” he said.
Hoover agreed, adding those living near areas where the land has been cleared may not even see cicadas this year.
“Members of Brood II may not be as abundant in Pennsylvania as they were in the past or as other broods — such as Brood X in 2004 and Brood XIV in 2008 — in part because of development and habitat loss,” he said.
Adult periodical cicadas are about 1 1/2 inches long with reddish eyes and orange wing veins. Koval calls them the aliens of the insect world because of their appearance. They are smaller than their cousins, the annual or dog-day cicadas usually seen and heard in the heat of late summer.
“They look alien in all stages, especially as adults because they are these gigantic, bumble bee-like creatures with huge red eyes,” Koval said. “And the noise they make is unlike anything else you will hear.”
Cicada nymphs spend 17 years from 2 to 24 inches underground, sucking nutrients from xylem cells in plant roots. In late April and May, they burrow to within an inch of the soil surface, where they await an undetermined signal for emergence.
“Soil temperatures reaching 64 degrees Fahrenheit and a light precipitation event seem to be prerequisites for cicadas to emerge,” Hoover explained.
When the time is right, usually in mid- to late May, the nymphs exit the soil through half-inch holes and climb a foot or more up trees or other objects. Within an hour, they shed their nymphal skins and become adults.
Adult cicadas are clumsy flyers, often colliding with objects in flight. Males begin their constant singing shortly after they emerge, but the females are mostly silent. When heard from a distance, the cicadas’ chorus is a whirring monotone, sometimes described as eerie-sounding.
On rare occasions when an adult eats, it sucks fluid from small twigs but does not feed on leaves. Ten days following emergence, mating takes place. Adults live up to four weeks above ground. Six to seven weeks after the eggs are laid, nymphs hatch and drop to the ground. There, they enter the soil, not to see the light of day for 17 years.
If you’d like to get a closer look at the insect that can live beneath us for 17 years, Koval recommends searching dry, upland forests with stands of oak trees.
Or, you can just follow eerie chorus.
A free fact sheet on periodical cicadas can be found on the Penn State Department of Entomology website.