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A Hole New Perspective on Brood X

Entomology Class Warms Up to Studying 17-Year Cicadas

By Aadit Tambe M. Jour ’22

Animation of cicadas emerging and receding into holes in the ground

Animation by Emma Howells

Brood X, the largest group of 17-year cicadas, are preparing to emerge broadly around our area in the coming week, experts say.

Most students would have walked right by the Swiss cheese-like ground near Memorial Chapel, or even picked up the pace. But when sophomore Colette Lord moved in for a closer look last Tuesday evening, she found the former inhabitants of the holes wriggling up a nearby tree.  

With excitement, she realized the vast horde of cicadas she had been waiting for all semester was finally ready to make its appearance—and she had likely made the first reported sighting of them in our area.

Lord is taking the course “Principles of Ecology,” in which students have the opportunity to conduct a deep dive investigation of the emergence of Brood X, the largest group of 17-year cicadas, which are preparing to crawl out of the ground across a 15-state region. They will likely be primed to emerge on a warm and humid evening this week in our area, as soil temperatures reach about 64 degrees Fahrenheit.

Students are studying the impact of soil temperature on the behavior and life cycles of the giant bugs, which measure up to two inches in length and play an important role in the ecosystem: Their holes and tunnels aerate the soil, and once they die, their bodies serve as an important source of nitrogen for growing trees.

The class has partnered with a larger effort studying the distribution, life cycle and evolution of the insects, called Cicada Safari, based at St. Joseph University in Cincinnati, to predict and track this spring’s emergence of Brood X. Students use a mobile application to record the data points they collect to contribute to their database of geographical distribution and abundance.

“It’s incredibly amazing that these things have been alive, under our feet, for nearly the entire lifetime of many of my students,” said Daniel Gruner, associate professor of entomology, who is leading the class. “In terms of this type of phenomenon of periodical emergence, this is the most extreme form that’s known around the world; and it’s happening right here—it’s a remarkable natural process.”

Students go out weekly to measure soil temperatures and track them in various locations where cicada emergence was recorded in 2004. Although few have yet emerged, the insects are preparing holes and tunnels—visible on the surface—that students have been seeking out and recording in recent weeks to estimate density.

“We know that the emergence is temperature-dependent—they develop more quickly if it’s warmer,” he said. “We want to see if the areas that warm up quickly are the ones with higher densities of cicadas.”

Students—particularly those who are afraid of bugs or attending class virtually outside the Mid-Atlantic region—can work on other ecology-related projects to document ecological diversity around them. But more than half the class of 46 students, Gruner said, is working on the cicada investigation.

Lord, who grew up in Frederick, Md., was 3 years old and too young to remember the last Brood X cicada emergence. Although she is intrigued from a scientific standpoint, she is personally not looking forward to billions of cicadas flooding outdoor open spaces.

“It's going to be more difficult to go outside and enjoy nature if there are billions of cicadas crawling around,” she said. “But as a biology major, I think it's a really interesting phenomenon because it only happens every 17 years.”

Cayley Hall, a junior majoring in environmental science and technology, has been waiting to hear their buzzing sounds at night around emergence holes in her designated site. The once-in-a-generation event is a welcome source of excitement in a semester that needs it.

“Knowing that they are emerging makes me more and more excited to see them,” she said. “Considering everything going online this semester, I’ve appreciated the opportunity for us to get out and about and kind of experience what this course would have been, were we in person.”


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