Some animals have learned how to use plants to heal themselves
On an expedition early in his career, Michael Huffman was watching a group of chimpanzees in an East African jungle when the primate researcher made a surprising observation. A mother chimp lay ill on a bed of branches in a tree as her two-year-old son climbed dangerously high. Too sick to scold or bring down her offspring, she simply ignored him.
A while later, the female chimp summoned the energy to climb to the ground. She then slowly ambled over to a shrub. Huffman watched as she removed several branches. After peeling back the bark, the chimp chewed on the inner pith. Next, she sucked out the juice.
From his research at Kyoto University in Inuyama, Japan, Huffman knew a lot about chimps and their behavior. He had never seen one of the primates sample or even show interest in this shrub before. So he asked his research assistant, Mohamedi Seifu Kalunde, what it was.
“Mjonso,” said Kalunde. A member of the local Tongwe tribe, Kalunde told Huffman the bitter-tasting shrub was medicinal. He explained that members of his tribe in Tanzania used it to treat stomachaches, malarial fevers and even gut infections caused by parasites.
Suddenly, Huffman recalls of that day in 1987, “I got really excited.” Huffman realized he just might have been the first university-trained scientist to watch an animal taking medicine. More specifically, he was likely the first scientist to realize the animal did so with an understanding that it was doctoring itself.
Over the following years, Huffman's follow-up observations revealed other chimps using the same shrub to cure themselves of ailments. Hisdiscovery has changed the way scientists study what animals eat, says Mark Hunter. He’s an ecologist at the University of Michigan in Ann Arbor.
“When we watch animals foraging for food in nature, we now have to ask, ‘Are they visiting the grocery store or are they visiting the pharmacy?’” explains Hunter.
Before his encounter with this sick chimp, Huffman had heard tales about animals self-medicating. As far as he knew, they were just that — stories. No one had confirmed a sick animal could seek out something it knew would relieve its discomfort or pain. Back then, most scientists thought only people knew enough to treat the sick with foods or other agents — medicines — to restore their health.
The day after he had watched the mama chimp suck out the mjonso juice, Huffman grew even more convinced that she had been deliberately treating herself. She seemed to have made a full recovery. In fact, he and Kalunde had trouble following her as she sped through the jungle, slapping the ground and grunting when her son did not keep up.
Later, the chimp’s feces confirmed Huffman’s hunch. He had collected samples of her feces from both before and after she sucked out the juice from the branches of the mjonso plant.
In the dung the chimp had passed before eating the plant, Huffman counted 135 eggs from a common parasitic worm. The worm attacks the stomach wall, causing pain. He then examined what she had pooped out just 24 hours after eating the plant. That dung contained a mere 15 parasite eggs, or just 11 percent as many. The finding suggested the chimp deliberately ate the mjonso to rid herself of a painful parasitic infection.
Over the years, Huffman would go on to witness other chimps eating mjonso and recovering within about a day. Evidence would show all had been infected with the same parasitic worm: Oesophagostomum stephanostomum (Es oh FAY go STOH mum STEF ah no STOH mum).
Any medicinal chemist would be wise to take note of such animal behavior, says Hunter, the ecologist. “We can learn a lot about how to treat parasites and disease by watching other animals,” he says.
Indeed, Huffman eventually worked with plant chemists to analyze what’s in mjonso. The shrub’s formal, scientific name is Vernonia amygdalina (Ver NON ee ah Ah MIG dah LEE nah). The experts found it contains several chemicals that are toxic to parasites. Huffman suspects mjonso contains the chemicals because plants, like animals, need to defend themselves against parasites. And the only way plants can get access to a protective poison is to make it.
The plant chemists discovered mjonso contains chemicals that poison cancer cells too. So drug chemists now are investigating how they might use the shrub’s natural chemicals to treat people with cancer.
When a ‘pharmacy’ is across the fence
There are other lessons to learn from observing what medicinal plants animals choose to eat, notes Juan Villalba. This biologist is an expert in animal foraging behavior at Utah State University in Logan. His work has pointed to the harm that can come from limiting the access that fenced-in sheep, goats, llamas and other farm animals have to certain plants.
Worldwide, these and other livestock face infection by another parasitic worm — a major killer called Haemonchus contortus (Hee MON kuss Kon TORT uss). The parasite feeds on the blood of its hosts. That kills or weakens the animals. For instance, sheep infected with this parasite produce less milk and lower quality wool. And unlike other intestinal parasites, this worm often goes undiagnosed until its host has weakened to the point of near death.
In a series of studies begun in 2008, Villalba’s team showed sheep infected with this worm often seek out plants containing high levels of tannins. Tannins are a group of bitter chemical compounds found in many plants, including oak, chestnut, sequoia and quebrachotrees.
After eating the leaves of the tannin-rich plants, infected sheep had only half as many parasite eggs in their feces as they did before eating these foods, Villalba found. “These animals are way smarter than we think,” Villalba concludes. That’s because not only do the sheep know what plants can make them feel better, they also seem to know how much of those plants to eat.
Sheep with higher numbers of worms will eat more tannin-rich plants, Villalba’s data show. But only up to a point. “When they overeat, they will start feeling negative effects and will stop,” he explains. These negative effects include stomachaches.
The real problem comes when people corral their livestock in pens. This restricts what plants are available for the animals to eat.
Of course, farmers can treat infected sheep with deworming drugs to kill parasitic worms. However, examining every sheep's feces for worm eggs takes a lot of work. That’s why many farmers often use drugs to treat an entire flock at once. Farmers do so whether each individual animal is infected or not. Over time, this kind of overuse can make a drug ineffective.
As Villalba explains, when large numbers of parasites are exposed to a medicine, a few may have a genetic mutation that keeps the medicine from killing them. (A mutation is a change that happens to a gene. A gene is a section of DNA that contains instructions for one or more activities of an individual organism’s cells.)
Although the medicine will kill most of the parasites, any that have the protective mutation will survive and reproduce. Indeed, only those parasites can reproduce.
Before long, the only parasites around to infect sheep will be those immune to the drug’s effects. Once that happens, the medicine is useless.
Farmers can avoid this by giving sick sheep the ability to seek out and eat medicinal plants. The farmers will need to use drugs only as a last resort, when their animals have an especially bad parasitical infection.
There is a lesson here for farmers who fence in their livestock, Villalba says. “We have to offer them more food choices,” he says. “The more choices, the better chance of them being healthy.”
Cigarettes for pest control
Nature’s pharmacy isn’t the only place where an animal may “shop” for medicine. Some birds may rummage in the trash.
Tobacco naturally contains high levels of nicotine. Even the butts of smoked cigarettes can contain substantial amounts of nicotine. This fact apparently has not escaped the attention of house sparrows and house finches — at least those around Mexico City.
Constantino Macias Garcia and his team at the National Autonomous University of Mexico examined 80 finch and sparrow nests on their Mexico City campus. They found the filter material from cigarette butts in every one. The birds had woven the filter’s fibers into these nests.
It remains unclear why the birds did so. Macias Garcia says nesting birds may rely on the fibers as a source of warming insulation. Or they may have learned through experience that the material helps keep their nests free of parasites.
Nicotine naturally repels a number of bird parasites, such as mites and lice. These parasites can weaken infested birds — especially young ones. But “the more fibers in the nests, the fewer mites and lice we found,” Macias Garcia told Science News for Students. His team reported its observations in 2012 in the British scientific journal Biology Letters.
One potential problem: Cigarette butts contain chemicals that cause cancer. So Macias Garcia is now looking for any signs that birds might suffer harm after making toxic cigarette butts part of their homes.
Sick monarchs find ‘pharmacy’ cafeterias
Parasites can plague insects too. At least one insect — the monarch butterfly — has found a way to treat its babies so that they avoid infection by a common and potentially crippling parasite. The butterflies do so by laying their eggs on a source of food that can be deadly to the parasites.
That’s what the University of Michigan’s Hunter discovered in 2010 while working in a greenhouse at Emory University in Atlanta, Ga., with Jaap de Roode. De Roode is an evolutionary biologist at Emory.
In this case, the parasite is a common protozoan called Ophryocystis elektroscirrha (OFF ree oh SIS tiss E LEK troh SKUR rah), also known as OE. (A protozoan is a type of single-celled organism. Some protozoa, including OE, cause disease.)
OE protozoa infect monarchs throughout the butterfly’s life cycle. Most of the damage the protozoa cause occurs while the butterflies are growing into adulthood, during their pupal stage.
Many infected monarchs die shortly after emerging from their chrysalis. (A chrysalis is the hard case that protects a butterfly while it is turning into an adult.) These infected butterflies simply can’t expand their wings.
Even those infected butterflies that do survive remain weak, vulnerable to disease and unable to migrate long distances. “It’s like going for a long run when you have the flu,” Hunter told Science News for Students. The parasite also reduces the number of offspring the butterflies can have. It can even shorten their lifespan.
In fact, OE has been described as this insect’s “arch enemy.”
Monarchs aren’t helpless against this foe, however. Careful observations have revealed how monarch mothers fight back against OE.
Female monarchs seek out milkweed plants to lay their eggs on. Once monarch larvae hatch, the newborn caterpillars feed on the leaves of the plant.
Usually, monarch caterpillars dine on any of several types of milkweed plants. However, Hunter and de Roode noticed that monarch caterpillars that ate tropical milkweed leaves had only about one-third as many parasites as those that ate swamp milkweed.
To probe why, Hunter and de Roode conducted an experiment. They put female monarch butterflies in an enclosed space. The researchers then gave the mothers a choice of plants on which they could lay their eggs: tropical milkweed or swamp milkweed.
Uninfected females showed no preference for either species. But the infected butterflies nearly always chose the tropical milkweed. What makes that plant special is that it produces higher levels of a group of chemicals called cardenolides (Kar DEN oh leidz).
Cardenolides cause the membranes surrounding cells to leak. Scientists suspect this makes it hard for those cells to work properly. And that can kill some organisms, including OE. But not monarchs. This butterfly has developed a genetic resistance to cardenolides.
So when a mother monarch lays her eggs on the tropical milkweed, her larvae hatch and begin eating the plant. And because the caterpillars ingest cardenolides as part of every meal, any protozoa infecting them will be poisoned and die.
“That is so unbelievably cool,” says Hunter. “Instead of laying her eggs in the grocery store, the mother monarch lays them in the pharmacy.”
Indeed, adds de Roode, “This shows even very simple creatures can use medicine.”
Scientists including de Roode and Hunter now suspect many other animals use simple types of medicine. Sometimes, observing what and how they use these natural medicines can teach us important lessons.
However, both scientists are quick to point out that mimicking an animal by using the same medicinal plant can be extremely dangerous.
For instance, notes Hunter: “There are some plants that a rhino or elephant might eat as medicine that would drop us dead in a heartbeat.”
cell membrane A thin layer of tissue surrounding a cell.
evolutionary biologist Someone who studies the adaptive processes that have led to the diversity of life on Earth. These scientists can study many different subjects, including the microbiology and genetics of living organisms, how species change to adapt, and the fossil record (to assess how various ancient species are related to each other and to modern-day relatives).
feces A body’s solid waste, made up of undigested food, bacteria and water. The feces of larger animals are sometimes also called dung.
forage To search for something, especially food.
genetic mutation Some change that occurs to a gene in an organism’s DNA. Some mutations occur naturally. Others can be triggered by outside factors, such as pollution, radiation, medicines or something in the diet.
larvae The young of many animals, including insects, fish and some parasites.
overdose To eat or drink more than the recommended amount of something that may be toxic, such as alcohol or medicines.
tannin A reddish and bitter plant chemical used to tan leather. Tannins are also a natural pesticide. Pesticides kill vermin, such as rats, insects and lice.
parasite A creature that gets a benefit from another organism, called a host, but doesn’t provide it any benefits. Classic examples of parasites include ticks, fleas and tapeworms.
primate The order of mammals that includes humans, apes, monkeys and related animals.
protozoan (plural: protozoa) Any of many types of single-celled organisms, most of them too small to be seen with the unaided eye. They include amoebas, parameciums and many others. Some can cause disease in humans and other animals.
resistance (as in drug resistance) The reduction in the effectiveness of a drug to cure a disease, usually a microbial infection.
Word find (click here to enlarge for printing)
S. Gaidos. “From dipping to fishing.” Science News for Students. May 21, 2008.
S. Ornes. “Honey’s hidden helper.” Science News for Students. May 9, 2013.
S. Ornes. “Cockroaches could be good medicine.” Science News for Students. Sept. 27, 2010.
S. Perkins. “Granola bars for cows.” Science News for Students. May 16, 2012.
E. Sohn. “Nature’s medicines.” Science News for Students. May 24, 2005.
Teachers questions: Questions for Wild medicine