Drew Carey, the comedian, once told the following joke:
“Oh, you hate your job?”
“Oh my god, why didn’t you say so! There’s a support group for that. It’s called ‘everybody,’ and they meet at the bar!”
Carey is referencing the habit of people to self-medicate with alcohol, using the promised inebriation from drinking too much as a way to drown out one’s sorrows. It’s probably not the best solution to one’s ailments.
But then again, Drew Carey wasn’t talking about fruit flies.
Fruit flies are bugs which feed off of the sugars in rotting fruit. If you live in the right temperate zone you’ve probably seen them swarm around a bowl of over overripe peaches or the like — they’re mostly harmless but frustratingly annoying. They’re also in what PBS called “a constant fight for their lives against endoparasitoid wasps.” The wasps “lay their eggs inside the body cavity of the baby fruit flies, and then they inject the infected insects with venom that suppresses their immune systems. The wasps feed on the flies, slowly eating them from the inside out, until the fly is gone and all that is left in the pupa is a wasp.” It’s not a fun experience, if you’re a fruit fly.
The good news for the fruit fly, though, is that these wasps don’t hold their booze well. On the other hand, for the fruit flies, a love of alcohol runs in the family.
Fruit flies locate rotting fruit from the smell of alcohol vapors which are emitted when the fruit’s sugars begin to break down. Once the flies detect the smell, they swarm to the fruit and start eating — and in doing so, make the equivalent of a trip to the local bar. Todd Schlenke, a biology professor at Emory University, told PBS that “they like their food with about 4% alcohol, or roughly the same alcoholic content as a bottle of beer.” For fruit flies, drinking with every meal is just part of life. (And it starts at an early age: fruit flies lay their eggs in the fermenting fruit, and as a result, their babies are born into the equivalent of a beer bath.)
As for the wasps, though, they’re not as fond of alcohol. If an infected fruit fly drinks enough fermented fruit juice, the alcohol kills the wasps, ridding the fly of the infection. So if you’re a fruit fly, getting drunk isn’t just force of habit — it’s also a way to save yourself from a pernicious parasite.
And it turns out, the fruit flies know it.
Schlenke and team set up an experiment to see if infected fruit flies act differently than those which aren’t playing host to wasps. The full paper is available here, but Emory’s eScienceCommons blog summarized the study conditions:
To test the theory, the researchers used a bisected petri dish filled with the yeast that fruit flies are normally fed in a lab environment. The yeast on one side of the dish was mixed with 6 percent alcohol, while the yeast on the other side remained alcohol-free. The researchers then released fruit fly larvae into the dish, allowing them to freely move to either side.
The result? “After 24 hours, 80 percent of the fruit fly larvae that were infected with wasps were on the alcohol side of the dish, while only 30 percent of the non-infected fruit fly larvae were on the alcohol side.” That is, most of the infected fruit flies went for the alcohol while the other ones were fine eating either option.
So, effectively, the fruit flies are self-medicating — by drinking to their health.
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Related: A drunk parrot wine bottle holder. Amazing.