Smashed, sloshed, drunk as a skunk—no matter what you want to call it, humans usually drink booze to have fun and reduce stress. But when animals get tipsy, it’s more about the calories.
In nature, fruit, nectar, and other plants can produce ethanol as they rot and ferment. And tons of animals—from African elephants to some 55 species of birds—have learned that fermented foods are efficient sources of nutrients. In fact, ethanol packs nearly double the caloric content of sugar. The caveat, of course, is that eating too much can produce some undesirable side effects.
But not, apparently, for the Oriental hornet. Laboratory experiments reveal the species, found throughout much of Asia, Africa, and Europe, can handle ethanol concentrations of a whopping 80 percent.
In comparison, most vertebrates suffer ill effects after consuming ethanol concentrations of more than 4 percent.
So why do these wasps have such a high tolerance? It may be because they have a mutually beneficial relationship with wild brewer’s yeast—the same kind we use for brewing beer and baking. (Read why insects are so vital to our planet.)
Yeast can’t survive cold weather, so they live—and reproduce—in wasp and hornet bellies during winter. In return, the yeast provides energy for the hornets by fermenting the fruit on which they feed. To cope with the yeast’s fermentation skills, the wasps may have evolved to carry multiple copies of a gene known to enable alcohol tolerance, according to the study, published October 21 in Proceedings of the National Academy of Sciences.
While getting insects sauced may sound trivial, there are numerous reasons scientists study drunk bugs: Both insects and primates have likely eaten fermented fruit for millions of years.
In fact, the so-called “drunken monkey hypothesis” suggests our ancestors’ ethanol-rich diet may be connected to the complicated relationship humans have with the substance to this day. (Read how alcohol harms our bodies.)
That’s why understanding the genetics of how Oriental wasps stomach so much ethanol could eventually lead to better treatments for alcohol-use disorders, which affects nearly 30 million Americans.
Taking it to the limit
When study leader Sofia Bouchebti, a behavioral ecologist at Israel’s Ben Gurion University, and colleagues fed that 80 percent absinthe-like ethanol solution to more than 2,000 Oriental hornets, “they were not able to fly properly or walk straight,” she says.
Happens to the best of us, of course. But what really shocked the researchers was how the insects rallied.
“Once I even saw a few individuals lying on their backs. I was pretty sure they were going to die, but when I checked back a few minutes later, they had completely recovered,” says Bouchebti.
What’s really remarkable is that while boozed-up hornets metabolized the ethanol and resumed building their nest without impairment, European honeybees fed the same alcoholic diet not only failed to function, they died within 24 hours.
Low concentrations of ethanol are beneficial to animals, says Bouchebti, but at higher concentrations, alcohol becomes toxic—as the dead honeybees illustrate.
This is why the scientists only used ethanol concentrations of 20 percent in their initial experiments—that’s the limit to what brewer’s yeast can naturally produce.
“We were so amazed by the lack of any negative effects at this concentration that we decided to increase the concentrations to determine the maximal concentration that hornets could handle,” which ended up being 80 percent. (Learn how the oriental hornet can harness the sun.)
“What I really would like to understand now is why [the Oriental hornets] adapted to such high concentrations,” says Bouchebti.
For instance, it’s possible that imbibing ethanol, which has antimicrobial properties, keeps the insects healthy and clean—especially since Oriental hornets are known to gather bits of rotting flesh to feed to their larvae.
‘Drunk off their gasters’
“What a cool study!” says entomologist Chris Alice Kratzer, who’s not at all surprised that some wasps have evolved the ability to metabolize ethanol. Hornets are the largest wasp species.
“Many fruits ripen in autumn, which aligns with the peak of wasp colony development in temperate climates,” Kratzer, author of The Social Wasps of North America, says in an email. “The ability to ingest fluid from rotting fruit is important for their survival.” (How wasps can recognize faces.)
“From personal observations, most species of social wasps cannot ingest ethanol without getting drunk off their gasters,” says Kratzer. (In wasps, “gasters” are the chunky part of the abdomen, similar to butts.)
Yellowjackets are particularly notorious lushes, hanging out in orchards and consuming rotting fruit until they can’t fly straight and even sometimes crash into each other, mid-air.
What’s fascinating though, is that the Oriental hornets appear to do so without much of a buzz, she says.
“This study is only the beginning,” says Bouchebti. “There is still so much left to discover.”
YEAR-LONG ADVENTURE for every young explorer on your list
FREE limited-edition frog drawstring bag with every Nat Geo Little Kids Book Bundle subscription