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There have been reports of animals medicating themselves to treat illnesses, but according to the research, you shouldn't go to a non-human pharmacist just yet.

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Tiger Moth Caterpillars

Fruit Flies

Chimps and Aspilia

Colobus and Charcoal


Elephants and Seringa
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Some animals are way smarter than we give them credit for. Crows can invent tools, some spiders customize hunting techniques, animals have even been observed medicating themselves to treat illnesses.

But animal behavior isn’t always what it seems, and this self-medication is a great example of that. There’s actually a whole field about this subject, called zoopharmocognosy, and it tends to pop up on the internet from time to time. For example, you might have read how elephants eat a certain tree to induce labor.

Or that some primates eat specific plants to get rid of parasites. But as cool as that sounds, and it sounds pretty cool, some of those stories are a bit problematic, at least scientifically. In some cases, the research isn't nearly as solidified as a lot of articles will make you believe.

So here are six examples of zoopharmacognosy and what the research really says. Although they are not the most famous examples, the best-studied cases of zoopharmacognosy are actually in insects, like tiger moth caterpillars. These insects eat multiple species of plant, but some of them are a bit unusual, because they contain harmful chemicals called pyrrolizidine alkaloids, or PAs.

These chemicals reduce the caterpillars’ ability to grow, but there’s also a pretty big benefit to eating them:. PAs protect the caterpillars against parasitoids. And a small caterpillar is better than a dead caterpillar any day.

These caterpillars are parasitized by several species of insect, including some flies that can make their lives pretty horrible. The flies lay their eggs on the caterpillars, and when they hatch, the young maggots burrow into the caterpillars and begin eating them alive. But if a caterpillar’s tissues are laced with PAs, it has a chance to survive this horror, because the alkaloids are even more toxic to the maggots than they are to the caterpillars.

In a paper published in PLOS One in 2009, researchers validated that idea in the lab, and they even found that parasitized insects ate more alkaloid-laced food than their unaffected counterparts. Kind of like they were taking more medicine. It’s unclear exactly how much they know why they’re doing what they’re doing, and the results were slightly different depending on how many fly eggs a caterpillar had on it.

But one way or another, it shows that they’ve found a treatment to kill the flies that ail them. It’s not just caterpillars that do this, either. Another insect that uses medicine to combat body-snatching parasites is our old friend the fruit fly.

If you’ve ever forgotten a peach in the back of your pantry, you probably know that these flies are attracted to rotting fruit. They lay their eggs on it so that, when they hatch, the little maggots have a sweet meal right in front of them. But sometimes, old fruit has yeast growing on it.

And as the yeast cells break down sugars in the fruit, they make ethanol, a type of alcohol that gives those baby flies a boozy meal. Ethanol isn’t good for developing baby anythings, but fruit flies can tolerate some of it because they have an enzyme to break it down. Still, generally, female flies do prefer to lay their eggs on fruit with low levels of ethanol, except when parasitoid wasps are around.

Kind of like with the caterpillars, tiny wasps can lay their eggs in fruit fly maggots, and eventually, the wasp larvae will devour them alive. But the wasps aren’t as tolerant of ethanol as fruit flies. For them, it causes various organ defects, and research published in 2012 showed that wasps were more than twice as likely to die if they parasitized flies that had been consuming ethanol.

What’s especially cool is that another study, published a year later, showed that female fruit flies decide whether or not to lay their eggs in boozy fruit based on the risk of parasitism. In the experiment, female flies that saw female parasitoid wasps preferred to lay their eggs in high ethanol food sources. But flies who were shown male wasps, who don’t lay eggs and so don’t pose a parasitism threat, preferred low-ethanol fruit.

Like with the caterpillars, though, this doesn’t necessarily mean the flies learned that ethanol was medicine. The researchers suggested that, instead, seeing a female wasp might trigger changes in the fly’s brains that cause them to prefer it. Although these insect stories are great, the whole idea of zoopharmacognosy really gained popularity based on work by primatologists.

Over the years, they observed various monkeys and apes eating plants used by local humans to treat ailments, especially intestinal parasites. This led them to hypothesize that the animals were also using plants as medicine, and their ideas trickled down into pop culture from there. But the truth is, in a lot of these cases, there just isn’t a ton of evidence, because these hypotheses are much harder to test in primates compared to with insects.

For example, it’s not really ethical, or practical, to put a bunch of monkeys in lab, and then give some of them parasites and see what they choose to eat. So scientists mostly have to rely on circumstantial evidence they gather by basically stalking primates in the wild. But those studies have been really interesting.

One example was from a paper published in 2001, where researchers recorded an odd behavior in chimpanzees in Tanzania. First thing in the morning, on an empty stomach, the chimps would fold up a leaf, often from an Aspilia plant, and then swallow it whole, without chewing. Other researchers had seen similar things before, but in this paper, the scientists took their work further.

They recorded 14 instances of this behavior and then followed the chimps closely to see, like, how everything came out. They were only able to observe pooping in seven of the animals, but for those seven, they found that the leaves passed through the chimps’ guts pretty much intact. More importantly, they noticed that there were often adult nematode worms present in the poop, parasites that spend part of their life cycle in the chimps’ intestinal walls.

The researchers didn’t find evidence of any nematode-killing chemical in the Aspilia leaves, though, like you might guess. Instead, they think the leaves may have more of a mechanical action. They have rough, slightly bristly surfaces, and the scientists think that allows them to physically scrape the worms off the chimps’ intestinal walls.

Kind of like swallowing a scrub pad. As you can imagine, the leaves also irritate the stomach, which makes it secret more gastric acid. Then, the acid passes through the intestine as well and may further repel the worms.

Of course, the sample size here is pretty small, and the researchers couldn’t experimentally test whether the leaves actually dislodge any parasites. So before we say anything for sure, we’ve got to get some science way more up close and personal with those chimp intestines. All examples of zoopharmacognosy aren’t about parasites, though.

Some animals self-medicate for other reasons. For example, red colobus monkeys living on the island of Zanzibar may use charcoal to prevent upset tummies. Farmers in Zanzibar have planted two species of non-native trees, mango and Indian almond, that have protein-rich, nutritious leaves that also happen to be loaded with tannic acid.

Tannic acid binds to proteins during digestion, which makes food less nutritious and also causes symptoms like nausea and vomiting in humans and, presumably, in monkeys. In high enough doses, it can also be toxic to liver cells. So to eat the mango and almond leaves safely, the colobus monkeys appear to take advantage of another resource that humans have inadvertently provided, charcoal.

Local farmers burn wood in outdoor kilns to make charcoal for cooking fuel. And colobus monkeys visit these kilns when they’re not in use to eat the bits of charcoal left behind. Charcoal doesn’t have any nutritional value, but it is good at absorbing things.

That’s why we use activated charcoal to treat people who have ingested certain types of poison. In 1997, when researchers tested the samples of charcoal the monkeys were eating, they found that they weren’t as good at absorbing tannic acid as medical-grade activated charcoal, but they were surprisingly effective. That made them hypothesize that eating charcoal allows the monkeys to safely eat the nutritious almond and mango leaves.

This may even be a learned behavior, too. Colobus monkeys that don’t live near farms and don’t eat these leaves haven’t been observed eating charcoal. And when researchers left some out, the animals had no interest in it.

To get really convincing evidence that the monkeys are using charcoal as medicine, though, you would have to do actual experiments, like feeding the monkeys almond leaves without charcoal and seeing if they got sick. But that’s logistically pretty challenging, and also just kind of mean. If you’ve tried doing the monkey bars on the playground recently, you might have found that as you’ve gotten older you’re a little less good at that and your arms got pretty sore.

And you might have even later treated that with a pain-killing rub like Icy Hot. If you did, you might not be alone. Based on some evidence, orangutans might do something similar after a long day swinging through the trees.

Starting back in 2003, scientists studying orangutans in Borneo noticed some of the animals chewing up the leaves of the Dracaena plant, spitting them out, and massaging the spit-leaf mixture on their arms and legs. The orangutans never swallow the Dracaena leaves, and they don’t rub any other leaves on their body like this, so scientists got curious. They learned that local people used Dracaena to treat sore muscles, and after some chemical analyses, they found that there was good reason for that:.

The plants contain chemicals called saponins, which can have anti-inflammatory properties. Specifically, they inhibit the production of inflammatory cytokines, signaling chemicals that promote redness and swelling. Muscle soreness after hard exercise is caused in part due to this inflammation.

So it’s possible that the orangutans were using the chewed up Dracaena leaves as a pain-killing rub. What makes this more likely is that most of the animals observed doing this were females who were hauling the extra weight of their offspring around and might have had some extra sore arms. But so far, only ten orangutans have been observed using Dracaena, and researchers can’t exactly ask them how their arms feel.

For all we know, the leaf-spit mixture just makes their hair really soft and shiny. They’re instagram influencers. Finally, one example of zoopharmocognosy that has gotten a lot of attention is the elephant and the red seringa tree.

As the story goes, a researcher studying elephants in Kenya observed one very pregnant elephant walk many kilometers out of its way to devour this tree. They had never seen any of their elephants eat this plant before, so it seemed odd that the pregnant one made such an effort to do it. Then, four days later, the elephant gave birth.

When the researcher talked to local women about this, they told her that sometimes they used a tea made from seringa leaves to induce uterine contractions and labor. So the researcher hypothesized that, maybe, the elephant was using the plant the same way. But even though popular literature cites this example a lot, it’s really not conclusive.

For one, it’s not clear which chemical in the seringa is responsible for inducing uterine contractions in humans. Or, if it has the same effect in elephants. Maybe that elephant would have given birth in four days no matter what she ate.

Generally speaking, we also don’t know how often pregnant elephants eat this tree. At the moment there’s just this one recorded observation and a cool hypothesis that needs more testing. All these examples go to show that zoopharmacognosy is really a very cool field, and that, in some cases, there is very strong evidence for it.

But in other cases the jury is still out. There’s still a lot scientists need to learn, and there are research methods they need to develop. But one way or another, this all raises interesting questions about animal learning, and whether we can discover potential medicines for ourselves by watching how animals deal with their ailments.

We just probably shouldn’t come to those conclusions too fast. Which is true of anything. We have to apply appropriate methodology and logic to any new discovery.

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