Fruit flies will drink alcohol from fermenting fruit to kill off wasp parasites that can grow inside of them.
As humans, we sometimes pay a price for drinking alcohol — in hangovers, or worse. But if you happen to be a young fruit fly, it turns out that alcohol can be just what the doctor ordered.
The pesky little fruit flies often show up when apples or bananas are left sitting around for too long on the kitchen counter. Most folks find them annoying, but Todd Schlenke can't get enough of them.
"I've been collecting flies in my backyard for a long time, sort of as a hobby," says Schlenke, an evolutionary geneticist at Emory University. He studies fruit flies and their mortal enemy: tiny parasitic wasps.
"These little wasps lay their eggs in the fly, and if the fly isn't able to kill them, the wasps hatch out and eat the flies from the inside out," Schlenke says. He says since fruit flies lay their eggs on rotting, fermenting fruit, the larvae that hatch can sometimes find themselves swimming in alcohol.
And that, Schlenke says, got him thinking: "I wonder if the alcohol can be used by the flies to protect them from being killed by the wasps."
Self-Medicating Fruit Flies
Schlenke says the first thing he needed to do was test how well the wasps could hold their liquor. It turns out some wasps can't even handle inhaling the fumes. No, they don't start slurring their words and hitting on that cute firefly at the end of the bar. But close.
"They basically get drunk. They can't stand upright, and they can't perform their normal functions, which is to lay a bunch of eggs in fly larvae and try to complete their life cycles," he says.
That means wasps are less likely to attack flies swimming in boozy fruit juices. But what if a wasp does succeed in laying its eggs inside a young fly? Schlenke found that if the fly larvae drink the alcohol, they can actually kill off the wasps developing inside them.
"And so the next question we asked was: Do flies know that? Do they purposefully consume alcohol once they're infected, in order to kill those wasps living inside of them? So we gave the flies a choice," he says.
In one half of the Petri dish, a delicious cocktail of baker's yeast, molasses and 6 percent alcohol. In the other half, the alcohol-free version. Infected flies overwhelmingly chose the booze.
"Essentially the fruit flies are self-medicating," Schlenke says. "They realize when they're infected, and they're seeking out a substance that helps cure them of that infection. And in this case that substance is alcohol."
Self-medicating exists all over the animal kingdom. Insects, birds and primates all have been known to eat special plants to rid themselves of parasites or other ailments. But, says Schlenke, this is the only situation that he knows of that has critters using alcohol as a medicine.
Can Drinking Kill Parasites In Humans?
And that raises the question: What about humans? After all, we get our share of parasitic diseases, too — everything from hookworm to malaria. Could alcohol help us get rid of parasites?
We posed the question to Peter Hotez, the dean of the National School of Tropical Medicine at Baylor College of Medicine in Houston. He's also president of the Sabin Vaccine Institute, which develops vaccines for parasitic infections.
Is there any chance that someone infected with, say, the malaria parasite might find a cure in a night of binge drinking?
Hotez says no. "It seems to actually have the opposite impact," he says, adding that studies of alcoholics show that chronic drinking can make some parasitic infections much worse.
But what about just a little alcohol? Can that help?
"The answer, as far as we can tell, is no," Hotez says. "The closest thing that comes to it is the gin and tonics that were used during the British colonial days to treat malaria. It wasn't because of the gin — it was because of the tonic, which contained quinine, which had an anti-malarial effect."