A Biologist Explores How Animals Heal Themselves

In 2010, Emory biologist Jaap de Roode published the discovery that monarch butterflies use medicine to cure their offspring of disease. His lab revealed how, if infected with a parasite, the female butterflies prefer to lay their eggs on a species of milkweed containing higher levels of a toxic chemical. The caterpillars eat the milkweed, ingest the toxin, and reduce the parasite load in their bodies.

With that finding, de Roode joined the vanguard of scientists uncovering how animals treat themselves for diseases.

“We showed how even an insect with a teeny-tiny brain can medicate,” de Roode says. “From there it was a natural progression to the understanding that, in principle, any animal can do it.”

In his new book, “Doctors by Nature: How Ants, Apes and Other Animals Heal Themselves,” de Roode explores the growing field of animal self-medication. He interviews scientists around the globe and describes research into how animals from ants to apes, birds to bears — even family dogs and cats — use various forms of medicine.

Scientific evidence of animal medication goes back to the 1980s when studies showed how wild chimpanzees chewed bitter plants or swallowed rough leaves to rid themselves of worms. 

Some scientists began arguing that animal self-medication requires great cognitive ability, memory and learning behaviors and was likely restricted to higher-order primates. That stance soon toppled with evidence of self-medication in a range of primates and other mammals.

De Roode's monarch butterfly discovery opened the door to a whole new level of understanding. It joined a handful of other published examples of insects tapping into nature’s medicine kit, such as wood ants that collect pieces of resin and bring them to their nests to reduce microbial infections.

De Roode is Samuel Candler Dobbs Professor of Biology at Emory, as well as director of Emory’s Infectious Diseases Across Scales Training Program, which immerses graduate students in interdisciplinary science to study and control infectious disease.

“At Emory you’ve got people coming together to work on infectious disease from so many different perspectives,” De Roode says. “It’s a holistic approach. That made it easier for me to say, ‘Let’s look at it from an animal’s point of view.’”

De Roode cites Frans de Waal, the renowned Emory primatologist who passed away last year, as another big influence on his thinking. “Frans showed that animals are similar to humans in so many ways, in terms of having culture, in terms of having empathy,” de Roode says. “So, then the idea that they use medicine is also not so farfetched.”

In the following Q&A, de Roode explains why he wrote the book for a popular audience, surprising things he learned while researching it, and what he hopes readers gain from it.

How did your love of animals and nature develop when you were a child in the Netherlands?

I just always loved animals and I read a lot of books about them. My mother was a tour guide at a zoo. I often went there with her and learned about the zoo’s conservation and breeding programs. So that’s probably how it started.

What’s unique about your book?

It’s the only book covering what we currently know about how many different animals can use medicine and the ways that we can benefit from that. There are so many potential applications of this knowledge, for everything from drug discovery to improving livestock caretaking, beekeeping and other aspects of agriculture. Even the way we take care of our pets.

I also tell the human stories of people making these discoveries. I tried to highlight people from a lot of different backgrounds and explain how the scientific method works. You can be a volunteer in the Congo or an undergraduate student in Mexico interested in birds, or an undergraduate student in Japan who loves cats. Many people don’t realize that students who just entered college can discover something exciting.

The story about the Japanese student is especially compelling, the way she demonstrated how when cats roll in catnip they coat their fur with a chemical that repels mosquitos.

It’s relatable science. We know that we take pills to protect ourselves from disease or to treat ourselves when we get sick. So, we can relate to the idea of animals using medicine. And the experimental work to test it tends to be straightforward.

That’s very different from describing the complicated methods involved in the development of an RNA vaccine. Most people don’t know what RNA is or how the immune system works. Whereas it’s easy to understand why self-medicating behaviors evolved in animals.

Everything that’s alive today has made it through millions of years of evolution. Plants have evolved all these interesting chemicals as defenses so they’re still around. And animals are still around because they’ve evolved to deal with the chemicals in plants in ways that benefit themselves.

What did you enjoy most about working on the book?

It was like going on an adventure, diving into stuff I didn’t know, learning all sorts of new things.

I really enjoyed the people that I met. It was especially fun to visit Mexico City and go into the field with researchers from the Universidad Nacional Autónoma de México. They conducted controlled experiments showing how birds use cigarette butts to deter parasites.

Did work on the book influence you as a pet owner?

I definitely look at my dogs differently. When they’re eating grass, I think about how that may be a relic behavior of their wolf ancestors to purge worms from their guts. I look at my dogs now as animals that know a lot of stuff that I don’t.

What surprised you the most during your research?

That the chemical inspiration for aspirin was discovered by bears. After waking up from months of hibernation, bears start eating plants that contain salicylates that help to relieve pain in their joints from lying still for so long.

I read a lot about Native Americans and learned that bears were often the most important animal for traditional medicine in their cultures. And then I learned that isn’t just true for Native Americans but also for traditional cultures in northern Europe and Siberia. Shamans would dress up like bears to gain their power and to learn their medical secrets.

European chemists eventually figured out how to make the more potent aspirin. But the power of plants containing salicylates has been known since ancient times, most likely learned by observing animals.

Many “discoveries” by scientists are actually “rediscoveries” of things traditional communities already knew.

Do you have another favorite example of animal-inspired medicine?

The funniest one I learned about is horny goat weed, used in Chinese traditional medicine. A goat herder noticed goats getting frisky and horny when they ate this weed. So, hundreds of years ago, they started using it to treat impotence. Recent laboratory studies have shown that when castrated rats are fed a chemical found in the weed they regain their libido.

What do you hope readers take away from the book?

Nature holds so many fascinating secrets. Discoveries that animals use medicine, and the insights that we can gain from them, gives us yet another reason to protect nature.

Evolution takes a long time but we’re destroying environments at such a fast rate that nature has no time to keep up. We’re losing species at a higher rate now than has ever happened in the history of the planet. And that is quite shocking.

One thing that you can do as an individual is to stop obsessing over your lawn. Lawn grass is the biggest crop in the United States, even bigger than corn. It looks nice but it requires all this water and fertilizer without really supporting anything. If you replace just 10% of your lawn with a garden containing native plants for pollinators you can help restore some natural habitat.

When you’re out in your garden, and you see all these animals, you’ll know they’re not just coming there for food and shelter. They’re also collecting medicine.

Story and design by Carol Clark. Lead video by Getty Images/Forrestbro