By Carol Clark
Birds do it. Bees do it. Even forest-dwelling ants do it. Increasing evidence suggests that a wide range of animals self-medicate.
“We need to pay close attention to how animals may use plants or other materials as medicine, because it has direct implications for human health and food production,” says Emory biologist Jaap de Roode.
De Roode wrote a review of recent studies on self-medication in animals for the current issue of the journal Science. De Roode and his co-authors, Thierry Lefèvre and Mark Hunter, recently published their own study showing that monarch butterflies use toxins found in milkweed to cure themselves and their offspring of disease.
De Roode will also be giving a talk on animal self-medication on Saturday, April 20, as one of 11 speakers set for TEDxEmory.
Until a little more than a decade ago, de Roode notes, primates were among the only animals besides humans thought to have the capacity for self-medication. Chimpanzees, for instance, had been observed in the wild eating plants with anti-parasitic properties but with little or no nutritional value.
Then some birds were found to line their nests with plants that ward off parasites, fungi and other pathogens. Just last year, ecologists in Mexico published a study suggesting that house sparrows and finches may be studding their nests with cigarette butts because nicotine reduces mite infestations.
The evidence for self-medication is actually stronger for insects. It’s easier to conduct laboratory experiments on them, and to clearly demonstrate whether an insect’s preference for a certain food delivers a benefit to fitness and survival.
“It’s now clear that animals do not have to have a big brain or advanced cognitive skills to use medicine found in nature,” de Roode says. “We’re seeing that these behaviors can be innate.”
Emory biologist Todd Schlenke, for instance, recently found that when fruit flies sense parasitic wasps in their vicinity, they lay their eggs in an alcohol-soaked environment, forcing their larvae to consume booze as a drug to combat the deadly wasps. And the larvae themselves, given the choice, prefer to eat food high in alcohol if, and only if, they are infected with the wasp eggs. The alcohol treatment is highly effective, greatly improving the survival rate of infected larvae.
No one has researched the possibility of whether alcohol could have a similar effect on humans suffering from blood-borne parasites.
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De Roode notes that insects and other animals may hold many medicinal secrets of potential benefit to humans.
Honey bees, for example, make a sticky substance called propolis from plant resins and incorporate it into the architecture of their hives. This resinous material has been shown to reduce bacteria and parasite loads in hives. A recent study showed that bees exposed to the spores of fungal parasites increase their resin foraging rates, suggesting that making propolis may be a case of self-medication.
In the wild, honey bees line the entire interior of their hives with resin to create what is called the “propolis envelope.” Many commercial beekeepers, however, select for bees that don’t gather resinous material, because the substance gums up the manmade hive frames.
Meanwhile, honeybees in the United States are suffering from die-offs that have wiped out nearly half of the hives needed to pollinate fruits and vegetables in the country. Drought, pesticides, viruses and other pathogens have all been suggested as possible causes of the bee deaths.
Could discouraging a self-medicating trait in bees also be a contributing factor?
“Those are the kinds of questions that are important to look at and think about,” de Roode says.
Related:
The monarch butterfly’s medicine kit
Fruit flies use alcohol as a drug to kill parasites
Fruit flies force their young to drink alcohol – for their own good
Tapping traditional remedies to fight modern superbugs
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