One of nature's true spectacles, early emergers of Brood X have started to arrive in Baltimore
Associate professor of biology John S. LaPolla, Ph.D. (Fisher College of Science & Mathematics) explained the emergence of the periodic cicadas now being seen on campus and throughout the region. LaPolla did a feature interview with Catherine Hawley of WMAR-TV channel 2 in the Towson University insect lab on Thursday, May 18, which aired that night.
What are we seeing right now are the early emergers of Brood X. These are periodic cicadas. This is a species that typically comes out every 17 years. So, the last time this brood would have emerged was in 2004. What sometimes happens, with periodic cicadas, is they have what are called stragglers. So the ones we are seeing now are the stragglers of Brood X and are coming out 4 years early. This is actually fairly well known with cicadas that they’ll come out a bit earlier than the 17 years. And, it’s usually at the four-year mark. So, 2017 is exactly when we expect to see some stragglers for the main emergence that should happen in 2021. This is a mid-Atlantic brood. Brood X encompasses most of Maryland but goes up into Pennsylvania, New Jersey and [down to] Virginia. There are about 15 broods emerging around the country.
It’s unclear, but these periodic cicadas have a really strange lifecycle. There’s several different species that live in the eastern United States. They have either a 17-year or 13-year cycle. This particular brood that we’re seeing now is one that has a 17-year cycle. But for reasons that are not entirely clear, it’s been documented that occasionally we’ll have early emergences, which is what we’re having right now, typically at the four-year mark. That is what we’re seeing this spring.
That part is still a little bit of a mystery in terms of how that works exactly. But the basic lifecycle is that they’ll emerge, as we see now. And this is about the right time—usually late May to early June. It’s been really warm this spring, so they’ve been coming a little earlier in May.
What they do is make these big mass emergences, and what happens is the males will go up the trees and sing and attract the females, they will mate and the females lay eggs—typically in the tops of trees. She’ll make a little slit in the tops of branches and lay usually around 20 eggs, and those eggs will hatch in a few weeks and little developing “nibs” will fall to the ground. The “nibs” are very tiny—usually about the size of a grain of rice. They feed on grass roots, and eventually they make their way to feeding on tree roots. One of the reasons we find them a lot at the edges of woods is it’s thought it provides access to grass. This is how they begin their lifecycle. They will live underground for 17 years before they emerge again.
Usually by the beginning of July their finished. We’re seeing them now, and they’ll start singing. I’ve heard a couple on campus just this morning. They’ll go through mating, and once that happens the adults die. One of the things we won’t get to experience this year as much is the songs of the species, which is pretty specular. They’re pretty quiet this year. It doesn’t sound quiet when it’s millions of them emerging, but we won’t quite get that this year because it’s not the main emergence we’re seeing. You can hear them, but they’re very faint as they’re singing along.
Could the effect of global climate change be affecting them? It’s unclear. One of the things is that these stragglers commonly come out four years before which is part of the natural biology which is probably what’s driving some of these different broods at different years in the first place.
One of the values of having an insect collection, like we have at Towson University, is it actually provides an historical record so we can look at specimens from decades ago and see when the emergence occurred and when did we have stragglers. This data provides an indication of changes that might be afoot. However, scientists would have to look at the longer timeframe. It’s important to record these records now because that will provide information to researchers down the line that might give us an idea if this is because of climate change or something else.
One of the things that’s exciting with social media now is we’re probably getting a much fuller picture of what these stragglers look like in the first place because it’s easier for people to report it. Whereas, not that long ago, it was tougher for us to get that data. Were probably getting more information and more precise locations that we used to get in the past.
This is one of the things we get to experience every 17 years. Scientists have wondered about these fascinating little creatures, how they evolved and why it is the way it is. There’s still a lot of questions that researchers are looking to answer about the periodic cicadas.
This story is one of several related to President Kim Schatzel's priorities for Towson University: TU Matters to Maryland.