In a few days, cicadas lurking just a few inches below the ground will emerge by the billions across Pennsylvania, Ohio and West Virginia. And believe it or not, this class of bugs—referred to by scientists as ‘Brood V’ cicadas—has been hanging out underground for 17 years.
But how exactly do cicadas know when to emerge en masse? Well, Kelly Hougland, a Ph.D. candidate at the University of Missouri, has been studying that very question. Recently, we caught up with him at Washington & Jefferson College’s Abernathy Field Station in Washington County to get the lowdown on this year’s big coming out party.
The Allegheny Front: So up until now, scientists have thought cicada emergence has a lot to do with soil temperature. But in your research, you’re looking into whether there might be a social component as well. Can you tell us about that?
Kelly Hougland: Well, periodical cicadas are actually fairly closely related to treehoppers, and treehoppers are known for their social interactions. The nymphs will either call to other nymphs to come where they’re feeding, or if they’re feeding in a group, they’ll move as a group. So they’ll start sending signals when they’re ready to move, and only when a critical mass of them has reached that decision will they move. And while cicadas aren’t quite that easy to interpret, they have access to social information: They’re noisy little things underground, and they also have the capability of perceiving these vibrations through the vibratory sensing organs they have in their legs. It’s very important that cicadas come out with other cicadas. If a male comes out too late, all the females have been mated with. If they come out too early, there aren’t any cicadas around to be eaten except for them, so they’re less likely to survive. Soil temperature can vary a lot depending on whether you’re right underneath a tree or there’s a plant on top of you. So if they’re coming out solely based on soil temperature, there’s a possibility that they’re not going to come out with their neighbors. Whereas if they’re incorporating soil temperature and social information, that means it might be a little bit too cold for one to want to come out, but if it hears all its neighbors coming out and it comes out, it’ll be better off.
LISTEN: “A Coming Out Party, 17 Years in the Making”
AF: So we had a very mild winter; we hardly had any snow. Does that impact when they emerge?
KH: It does, since they rely on soil temperature to know when and what year to emerge. Seventeen years ago, here, they started emerging on May 30. But it’s projected they’re going to start emerging around May 20 here.
So as winters have gotten warmer and springs have gotten earlier, they are emerging earlier. Once they’re out, they’re still sensitive to temperature, and if it’s too cold, they can’t fly. So if they come out too early and there’s another frost, all the ones that have come out early will die, because they don’t have the soil to insulate them.
AF: So how many cicadas are underneath our feet?
KH: There can be up to 300 per square meter. There will probably be hundreds of thousands that come up in this wooded area. But across all of Ohio, West Virginia, Kentucky and Pennsylvania, where they’re coming out this year, there will probably be billions.
AF: And ecologically, do they have a function in this landscape?
KH: They do provide a food source to numerous predators, and they satiate the predators so they eat less of other things. But another interesting thing is their tunnels, because a lot of things use them. There are species of salamanders that can’t dig their own tunnels, and I’ve seen spiders use their tunnels as well. So once they come up, those tunnels stay open. And depending on how much it rains and the soil type, those tunnels can stay there a long time.
Just the act of billions of individuals tunneling up through the ground has a huge impact on the soil. For instance, it can introduce water deeper into the soil from the top.
AF: So what exactly are they doing down there for 17 years?
KH: Growing, for the most part. They don’t live a very exciting life underground. The entirety of their world is this tiny little chamber they dig out and a root that they’re sucking on. At this point, they’re about the size of the tip of your pinky finger or your thumb, depending on whether it’s a male or female and the species.
When they first go into the ground, they look a lot like shrimp. Now, they’ve got this light brown bulbous body. Their front legs are these intimidating claws that almost look like mantis claws. And, of course, they have these gorgeous bright red eyes.
AF: You say they’re beautiful, but a lot of people think they’re creepy.
KH: Well, I work with bugs for a living, so I have to find them beautiful! I love it when they’ve fully emerged and you walk through a forest edge and there will be hundreds flying away from you as you walk along. And it’s kind of like walking through some sort of fairy-filled landscape. It’s pretty cool.
AF: The thing that most people know about cicadas is not what they look like, but what they sound like. So how does that work?
KH: Once they emerge, it’ll be about a week before they start calling. They’re very soft, and the organs that the males use to call need to be very stiff to work. They just have these stiff ridges right underneath their wings, and if you’ve ever crunched the side of a water bottle, that’s essentially how they work. They buckle it and it makes a click, and then they unbuckle it and it makes another click. They do it so fast that it makes an actual tone.
Why they make the noise is to attract females. Proportionally, if you were to have a cicada the same size as us, they would produce the same level of sound as a jack hammer. So they make quite a racket, especially when you get all of them together up in a tree.
AF: And what’s something people don’t know about cicadas that they should?
KH: Well, one thing people don’t realize is that they do feed as adults. They eat the water-rich stuff in trees. That’s why when you’re underneath a tree that has a lot of periodical cicadas in it, it feels almost like it’s raining. That’s actually cicada urine.
AF: So they pee on our heads.
KH: Yes, they pee on our heads. All the time. And come June, be ready.
Kelly Hougland is a Ph.D. candidate at the University of Missouri who’s been studying the social behavior of periodical cicadas. If you want to help document the ‘Brood V’ emergence this spring, check out this cool citizen science project. Photo (top): Dan Keck via Flickr