150-Year-Old Frogs Collected by a Founding Smithsonian Naturalist Helped 21st-Century Scientists Track How Pesticides Devastated Amphibian Populations in Illinois

In celebration of the upcoming Save the Frogs Day, learn how scientists used historic cricket frogs to connect hormone-altering industrial chemicals to amphibian declines in the Midwest

At less than two inches long, the tiny, warty Blanchard’s cricket frog may look unassuming at first glance. But museum specimens of this small species have had an outsized scientific impact. The frog, which makes a breeding call that sounds like metallic clicking, has helped scientists understand the profound impact manmade chemicals have on amphibians.

As part of the upcoming exhibition “From These Lands,” the National Museum of Natural History is displaying a jar full of cricket frog specimens, collected by Robert Kennicott (1835-1866) from southern Illinois in the late 1800s. On first glance, the assemblage of amphibians may not be eye-catching, but these frog specimens serve as a time machine to researchers, allowing them to glimpse a long-lost Midwest ecosystem. 

When the frogs were collected sometime prior to 1873, pesticides were not widely used in the southern part of Illinois. As a result, the specimens provide a natural baseline for scientists to compare with modern frog populations. In doing so, scientists have found that pesticides likely caused a dramatic decline in the region’s cricket frog population.

Once the most common amphibian in Illinois, the cricket frog is now rare in parts of the state with dense human populations, like the Chicago region. The frogs are vulnerable to human development because they live near slow-moving streams, ponds and ditches that are susceptible to runoff and pollution from chemicals like pesticides. Pesticides leech into water bodies and disrupt amphibian hormones and reproduction by changing the ratio of males to females in a species, delaying maturation and reducing the size of the animals at metamorphosis — all undermining their population.

In the early 2000s, scientists suspected that hormone-altering chemicals were to blame for the decline of the once ubiquitous cricket frog. To confirm their hunch, the researchers studied cricket frogs collected throughout the state and deposited in museum collections, including those housed at the Smithsonian, between the mid-19th century and 2001.

Their findings were illuminating. Beginning in the 1930s, the rise of industrial compounds like the pesticide DDT and polychlorinated biphenyls (PCBs) coincided with an increase in intersex cricket frogs. These frogs had altered reproductive traits, with either testes that produce egg cells or both a testicle and ovary, giving them lower reproductive success. There were also more intersex frogs and less female frogs in the more urbanized northeastern portion of the state than in other regions with less intensive agriculture and urbanization. However, the frogs also tell a story of gradual recovery. In more recent decades, as DDT use declined, sales of the pesticide were banned and industrial pollution came under stricter control, the proportion of intersex cricket frogs has also decreased.

Today, the cricket frog is still experiencing severe, long-term declines due to chemical pollutants, habitat loss and climate change, and it is listed as endangered in several states. The frogs are living in a very different world than they were when they were collected by Kennicott, an early Smithsonian explorer and herpetologist who spent most of his life in Illinois.

Kennicott was a dedicated naturalist passionate about understanding the natural world. His father was a horticulturalist, and as a child living in Illinois, Kennicott spent most of his time outdoors, collecting plants and animals. When he was just a teenager, he began sending specimens of frogs and birds from Illinois to the nascent Smithsonian Institution.

Despite being chronically ill from a young age, Kennicott completed major expeditions all across the North American continent. In his early 20s, he served as founding director of The Chicago Academy of Science and established a natural history museum at Northwestern University. In the late 1850s, he joined the Smithsonian as an explorer and cataloger, and he spent much of the rest of his career collecting specimens for the museum. He was a member and co-founder of the Megatherium Club, a tight-knit group of young naturalists who lived in the Smithsonian’s castle as they helped build the foundation of the Institution’s massive collection.

Kennicott contributed hundreds of specimens and objects over his short lifetime. Many of these contributions — including this jar of cricket frogs — document not only an individual species but also an environmental snapshot of a distant time.

Ashley D'Souza | Read More

Ashley D’Souza is a science writing intern at the Smithsonian’s National Museum of Natural History, where they cover natural history research and collections news for the museum’s blog, Smithsonian Voices. Ashley is currently completing their master’s degree in science writing at MIT, where they write about any and all things wildlife. They also run the blog and YouTube channel, Confessions of a Bird Freak. In their free time, Ashley can be found wandering through the woods with their camera and binoculars and talking to trees and birds. See more of Ashley’s work at https://ashleydsouza.contently.com/ and https://confessionsofabirdfreak.com/.