YORK COUNTY, Pa. (WHTM) — Some of the area’s first 17-year “Brood X” cicadas have emerged in Gifford Pinchot State Park, according to observations posted in the “Cicada Safari” mobile app — or more precisely, according to the man behind Cicada Safari, Dr. Gene Kritsky of Mount St. Joseph University in Cincinnati.

Officially, for the record, his title there is dean of behavioral and natural sciences. But you can just think of him as the world’s dean of cicadas.

Where were you in 2004, if you’re old enough to remember? 1987? Cicadas have been marking time for people for a lot longer than that.

“And then 1732, what we know about that emergence is that a friend of Ben Franklin’s gave him the details,” Kritsky said, ticking off facts about emergences through the years. He said one reason Brood X is so famous is not only because it emerges in such a large swath of America but because the swath includes big, old cities from Philadelphia to Cincinnati. Search newspapers dating back to Colonial times, and every 17 years, you’ll see reports of the “locusts.”

By the mid-1800s, citizen cicada scientists were collaborating — crowdsourcing, you might say, two centuries before the Cicada Safari app. “Back in the 1840s!” Kritsky reiterated. “We think we’re so clever today.”

Kritsky said you can go to the Gloria Dei Old Swedes Episcopal Church in Philadelphia and meet the descendants of revolutionary cicadas, documented being specifically right there, at that location, back then.

In 1987, Kritsky’s answering machine tape ran out of space. In 2004, his email inbox was full. Today, 105,000 people and counting — another 5,000 each day, he said — have downloaded Cicada Safari.

For those of us who have trouble managing to keep track of an upcoming dentist appointment, these invertebrates’ command of the calendar seems remarkable. How do cicadas count years?

“They’re sucking on tree roots underground,” Kritsky said. “And during the winter months, there’s no fluid flow from the roots to the leaves.” Then the fluid starts flowing again in the spring, and the cicadas “know” a year has passed.

But “what we have no idea about is how they remember what number it was,” Kritsky said. One of nature’s enduring mysteries.

As everyone knows, the “X” in Brood X is the roman numeral 10, not the letter “X.” (Everyone doesn’t know it. Your cicada correspondent here didn’t know it until being diplomatically corrected by Kritsky when he — uh, I — pronounced it like the letter.)

As even fewer people surely know, a brood of cicadas is a cohort of cicadas that emerge on the same schedule — not necessarily cicadas of the same species. Brood X has three different species. (Kritsky can easily identify them by their calls or by looking at their bellies.)

Speaking Wednesday with my cousin Avery Meetre in Washington, D.C., I let it slip that the reason I know she’s turning 30 this month is because cicadas were everywhere during her bat mitzvah in May 2004, when I know she was 13. I also know 13 plus 17 equals 30.

“Are you insulted to know the reason I know you’re 30 this year is because of cicadas, not because I have any idea what year you were born?” I asked her.

No, she said. She’s not insulted. And I think she meant it.

“They are the bugs of history,” Kritsky said. “They lock in memories.”