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Josh Davis 29 Apr 2015, 17:50

So far, the majority of evidence for animals self-medicating—either by ingesting or applying substances with medicinal properties to treat or prevent disease—has been documented in vertebrates, and more specifically chimpanzees (Pan troglodytes). But there is a growing body of evidence that a wider and wider range of animals seek out plants and other substances specifically for their healing properties.

Known as zoopharmacognosy (literally “animal-drug-knowing”), the most common examples involve parrots eating clay to absorb toxins in the gut or dogs eating grass to make themselves sick. North American brown bears (Ursos arctos) are also known to make a paste of osha roots and saliva to rub through their fur to repel insects in a similar way to how many species of birds wipe ants through their feathers to rid themselves of lice. But evidence of self-medicating in insects has until recently remained scant.

Recent research has shown that certain species of bumblebee might seek out nectar high in alkaloids—such as nicotine—when infected with a gut parasite. The alkaloids were shown to reduce the number of parasites after the bees had had their tipple of nectar. Since this might be an example of self-medicating amongst insects, a team from Queen Mary University of London (QMUL) decided to put it to the test.

They found that bumblebees (Bombus impatiens) infected with the gut parasite Crithidia bombi were more likely than healthy bees to feed on nectar laced with nicotine. Whilst the nicotine reduced the level of parasites in the insects' gut for a few days, interestingly it didn’t actually increase the bees' life expectancy when compared with infected bees who hadn’t sampled the fortified nectar.

This might seem odd, but as the researchers note, infection entails an array of harmful effects to the bees and any reduction in the severity of sickness might therefore be of benefit to not just the individual bee, but the colony as a whole. For example, they might be less likely to spread the disease to other members of the hive. As Dr. David Baracchi, co-author of the study, explains: “While it’s clear that there is some benefit to nicotine consumption for parasite-infected bees, a key challenge now is to discover exactly how such natural medication limits the impact of the disease on the bees’ society.”

However, whilst consuming the nicotine reduced the number of parasites, it also had negative effects. It appeared to suppress the appetite of infected bees in a similar way that smoking does to humans, but the nicotine was even more damaging to uninfected bees. If given a daily diet containing the drug, the life expectancy of the bumblebees plummeted.

Another study released earlier this year found similar self-medicating results, testing eight different chemicals found in nectar and the impact they had on the bumblebees' health. They found that all reduced levels of infection in the pollinators. So it seems that the evidence is gathering that bees are able to select flowers based on the medicinal properties in nectar to regulate internal parasites, and it might be a hell of a lot more common than we originally thought.  

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