In 1987, in Tanzania, a chimpanzee named Chausiku caught the attention of primatologist Michael Huffman by exhibiting unusual behavior: **chewing the bark of the Vernonia amygdalina bush**, commonly known as bitter leaf, a plant not part of its usual diet. Bitter leaf is known in Africa for its **medicinal properties against fever, intestinal parasites, and stomach pain**, leading Huffman to suggest that Chausiku might be self-medicating.
Surprisingly, just 22 hours later, Chausiku went from being apathetic to regaining its energy, confirming Huffman’s hypothesis as **the first documented case of self-medication in animals**. Since then, numerous examples have been observed revealing that self-medication is not exclusive to humans or closely related species, but a more common and varied behavior than previously thought.
## Which species heal and prevent their diseases?
### 1. Caterpillars that fight internal parasites
In 1993, biologist Michael Singer observed woolly caterpillars feeding on **toxic plants** such as artemisia and crotalaria. These plants contain pyrrolizidine alkaloids, which are lethal to internal parasites, such as flies that lay eggs in their bodies.
Singer discovered that **sick caterpillars prioritize consuming these plants**, increasing their chances of survival. Although the alkaloids are also toxic to healthy caterpillars, the benefits outweigh the risks in sick ones, representing a compensatory strategy similar to the side effects of drugs in humans.
### 2. Monkeys and lemurs that produce insect repellents
In South America and Madagascar, **capuchin monkeys and lemurs use the millipede** ***Orthoporus dorsovittatus*** **as a repellent**. They bite them and rub their bodies with the viscous substance they secrete, rich in benzoquinones, a chemical compound that repels mosquitoes and ticks. This behavior intensifies in times of increased insect presence, **acting as a natural defense against diseases**.
### 3. Chimpanzees healing their wounds with insects
In Gabon, a study in 2022 documented how **chimpanzees treated their wounds by applying crushed insects**. This behavior was not only individual: they also shared insects among group members to use them on their injuries. Although it is not certain whether this practice speeds up healing, the context and repetition suggest a rudimentary form of social self-medication.
### 4. Urban birds using cigarette butts as prophylaxis
In Mexico, researchers discovered that **sparrows and finches add cigarette butts to their nests**. The nicotine present in the butts acts as a **repellent against parasites like mites and lice**. Although this strategy reduces infestation, it also implies toxic effects for the chicks. However, the net balance seems to be positive, as nestlings from nests with butts weigh more and show better overall health.
### 5. Monarch butterflies protecting their offspring with toxic plants
When **monarch butterflies contract parasitic infections**, they choose **milkweed with high levels of cardenolides**, toxic compounds that **decrease the chances of infection in their eggs**. This instinctive behavior ensures the survival of the next generation, demonstrating a surprisingly effective adaptive strategy.
## Other animals that can heal themselves
In addition to birds and chimpanzees, **bees, lizards, and elephants** also share this survival trait: self-medication.
These animals are characterized by **eating things that make them feel better, prevent diseases, kill parasites like flatworms, bacteria, and viruses, or simply aid digestion**.
## A common yet unexplored behavior
**Self-medication in animals combines physiological and social factors**. Some behaviors seem innate, such as a preference for specific compounds, while others are learned, based on the relief or benefit experience after certain **actions that can help species heal and prevent their diseases**.
According to biologist Jacobus De Roode, self-medication has likely existed since the origins of the animal kingdom: “Where there are parasites, there are ways animals take care of themselves.” This emerging field not only reveals **the natural ingenuity of species**, but also offers **inspiration for new medical strategies in humans**.
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