A collection of winged insects encased under glass.
CAS Magazine: Faculty

Curious Little Things: Uncovering the Wide World of Insects with Martha Weiss

Cicadas that change ecosystems. Moths that remember being caterpillars. Spiders that cosplay ants. Entomologist and Professor Martha Weiss studies the colorful, crawly and creepy insects that surround us.

The life of Martha Weiss is segmented, bisected by the first time she saw cicadas. 

“Having grown up in California, I never had the pleasure of experiencing a periodical cicada emergence until 2004, when Brood X made its last appearance above ground in Washington, DC,” reminisced Weiss. “There were cicadas everywhere – crawling up out of the soil, marching across the sidewalks, climbing trees and stop signs and fence posts… Watching adults emerge from their nymphal cases and spread their wings was magical, and the cacophony of chorusing males was the perfect soundtrack to all that insect action! As a scientist who studies insect behavior, I was of course enchanted, and resolved that if I were still here 17 years hence, I’d find a way to study these amazing creatures.”

Periodical cicadas, which spend most of their lives underground feeding on the roots of plants and trees for long, dark years before emerging by the billions to reproduce and die, are not often described in such romantic terms. 

A woman in a chunky green sweater sits at her desk surrounded by books and files. She holds a mug and looks at the camera with a warm smile

Martha Weiss in her office on the Hilltop.

Early Puritan colonists were shocked by the cicadas and worried that, in addition to eating away at the forest, they were harbingers of sickness or disease. William Bradford, the governor of Plymouth Colony, described them as a “great sort of flies like for bigness to wasps or bumblebees, which came out of holes in the ground and replenished all the woods, and ate the green things, and made such a constant yelling noise as made all the woods ring of them, and ready to deaf the hearers.” Nearly 400 years later, many are still fearful of the large insects, scared away by the red eyes of periodical cicadas, their huge size, and loud screeches.  

For scientists like Martha Weiss, however, cicadas are not only objects of wonder but peculiar organisms that provide invaluable insight into the natural world. 

An Appetite-altering Lurker

Bradford was incorrect in presuming that the cicadas ‘ate the green things;’ unlike locusts, adult cicadas feed on plant fluids, and do not eat leaves at all. However, as any biologist would predict, they become an unforeseen source of food for a myriad of animals. 

In anticipation of Brood X, among the largest populations of periodical cicadas, Weiss began preparing a research team to study their arrival in Mid-Atlantic forests in 2021. These adult cicadas, the children of the same insects that had fascinated her in 2004, hadn’t been seen for 17 years. 

A black insect with bright red eyes and brownish orange wings.

A cicada during the 2021 emergence. Photo by Martha Weiss.

Weiss partnered with her longtime collaborator John Lill, a professor at George Washington University, and additional researchers from his institution and the University of Maryland, College Park. The team set out to study how birds in temperate forests altered their diets when hordes of new insects seemingly appeared out of nowhere. 

“We wanted to see whether the birds that ordinarily ate the forest caterpillars that we have long studied would switch over to the novel prey when a gigantic pulse of insect food appeared in the forest, and if so, what the consequences would be for the rest of the forest food web,” Weiss said. 

The research team’s findings, released this past fall, provide biologists and lovers of insects with an intimate look at one of nature’s most fascinating curiosities. They were so groundbreaking that the research was featured on the cover of Science, one of the world’s leading academic journals. 

“Our results demonstrate the pervasive ecological impacts of periodical cicadas on species interactions and patterns of energy flow in the eastern forests of North America,” said Weiss. “Although they make an above-ground appearance only once in a generation, there is typically at least one brood appearing somewhere in this vast region every spring — and each time they appear, these insects rewire forest food webs and leave behind an ecological footprint on the landscape.” 

Weiss’s team drew on 983 observations from bird enthusiasts in the Mid-Atlantic region, forming a large-scale view of bird-cicada interactions across Brood X’s habitat. The team documented more than 80 species of birds eating cicadas, including many that don’t regularly consume insects as a primary food source — as well as those that do

“As a consequence, their predation rate on caterpillars decreased dramatically, resulting in a doubling of leaf-feeding caterpillar populations,” said Weiss. “Double the caterpillars meant double the leaf damage, suggesting that the cicadas indirectly  disrupted patterns of energy flow throughout a wide swath of eastern forests.” 

A Knack for Spreading Wonder

For Weiss, communicating scientific findings to the public is as important as conducting research in the first place. As Brood X’s re-emergence approached, Weiss and her collaborators sought to educate local youth who would be experiencing cicadas for the first time. 

Four people sit at a wooden table in the woods. They are examining leaves.

Students conducting research in the field with John Lill. Photo by Martha Weiss.

“We thought that the cicada emergence was an amazing, once-in-a-generation opportunity to teach kids about insects, and to help tip the balance ‘from fear to fascination,’ as our environmental education collaborator [at Conservation Nation] Diane Lill puts it,” said Weiss. 

The team created a comprehensive guide to cicadas for elementary and middle school students, hoping to generate interest in one of nature’s greatest oddities. The digital resource, found at www.FriendToCicadas.com, is now periodically updated with additional information for different broods as they appear across the eastern half of the United States. 

“In 2004, I had a 6 year old and a 4 year old, and it was so exciting for me and my kids to witness this unbelievable biological occurrence,” said Weiss. “However, not every child in the neighborhood was thrilled about it — in fact some were quite scared. They were just so full of questions, like ‘Where did they come from? Why are there so many? What do they eat? Can they hurt me? Why are they so loud?’”

By sharing informative and fun materials about cicadas with young children, Weiss not only hopes to allay their fears, but incite curiosity and wonder at the natural world. 

“Insects are the most common and widespread animal group on earth,” said Weiss. “While there are a few species that are dangerous and can spread diseases, the vast majority are not harmful to people, and, in fact, are essential to us. They are pollinators, they move plant material around, help with decomposition and they are lunch for a huge diversity of other animals. Without insects, entire food chains would collapse.”

A Web of Wonder

Two women look at insect specimens contains in a wooden case with a glass cover. One stands and looks down at the box while the other sits.

Martha Weiss examining insect specimens with a student.

Weiss has published research on an array of plants, insects and the interactions between them. In other words, she’s not just the cicada scientist.  

After earning her Ph.D. from the University of California, Berkeley, where she studied flowers that change color to signal their pollinators, Weiss began her career as a botanist. 

“The plants take advantage of the insects’ color vision and learning ability to teach their pollinators which flowers to visit,” Weiss said. “The insects are directed to flowers that will reward them with nectar, the flowers receive efficient pollination service and everyone wins!” 

Weiss and her students have continued to investigate insect learning and memory, as well as ecological interactions between plants and insects. In the first demonstration of retention of memory across metamorphosis in moths and butterflies, she and her former graduate student Douglas Blackiston (G’07) showed that a moth could remember experiences it had as a caterpillar. 

Funded in part by a Fulbright Fellowship, Weiss recently traveled to Southern India where she teamed up with Divya Uma (G’10) to study the behavioral ecology of insects and spiders that look and act like ants.

“India is literally crawling with amazing ant mimics; the remarkable resemblance makes them less likely to be eaten by predators that rightly steer clear of what they take to be the tiny aggressors,” Weiss said. 

And Martha isn’t done studying cicadas yet — her team is traveling to Chicago this year to observe the rare simultaneous emergence of adjacent 13-year and 17-year broods of cicadas. The last time both of these broods emerged at the same time was in 1803. This isn’t just the event of a lifetime for an entomologist — it’s the event of the century. 

This time, instead of looking at birds’ appetites for cicadas, the team plans to turn their attention to ants. 

“These tiny creatures play a number of important roles in their forest communities, and we want to investigate the ecological implications if ants ‘walk off the job’ when the cicadas arrive,” said Weiss. “We are thrilled to be able to travel to Illinois for the double emergence; cooling our heels until 2038, when the DC cicadas will come back above ground, was not going to work — it’s way too long to wait for answers to our questions!”

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