It is thought that females might be using the plant to treat their aching arms after carrying their babies through the trees. Sergey Uryadnikov/Shutterstock

Many animals over the past few decades have been revealed to self-medicate. From parrots eating clay to coatis coating themselves in resin, the use of naturally occurring plants and minerals to treat themselves is not exactly uncommon.

But this has never before been observed in wild orangutans, until now. Not only that, but this is the first time it has been proven that any great ape – including both chimpanzees and bonobos – uses deliberate external self-medication.

The apes were first observed chewing leaves, and then rubbing the lather formed due to the saponins released on themselves, a few years back. So far it has only been reported in the Bornean orangutan, and not in either of the other two species of the Asian great apes. Initially, the plant they were using was misidentified as being Commelina, but further and more detailed observations showed that it was actually a species known as Dracaena cantleyi.

The medicinal plant Dracaena cantleyi found growing on the forest floor. Mokkie/Wikimedia Commons

The leaves of the plant are incredibly bitter, and the observations show that the apes chew on the leaves to make the lather before spitting out the remaining wadge. This proves that the orangutans are not eating the plant, but are presumably only interested in the substances it exudes, something that must be worth braving the disgusting taste in the first place.

And so the researchers set out to see whether or not D. cantleyi actually has any pharmaceutical properties, and if so what the apes might be achieving by rubbing the lather on their fur. Tests have now shown, the results of which are published in Nature, that the plant does indeed have medicinal properties, and is, in fact, an anti-inflammatory.

The researchers think that the apes may have been seeking some form of relief from aching arm and leg muscles. This is supported by the fact that over a period of studying a total of 50 orangutans, five of the seven apes observed self-medicating in this way were mothers carrying infants, and the authors suggest that the carrying of the babies may be putting strain on their arms, giving them a reason to seek out relief.

What’s even more fascinating about this discovery is that the local indigenous people living in Borneo also use the leaves of the same plant to treat body aches and pains. This is intriguing for another reason entirely, because some studies of ethno-medicine have suggested that such indigenous communities may obtain some of their knowledge of medicinal plants by watching sick animals using them first.

[H/T: Mongabay]