An alcohol-only diet would throw most species for a loop, but new research suggests certain hornets can live apparently unimpaired—with an 80 percent ethanol sugar solution as their sole food source.
Fruit flies, tree shrews, and many other animals naturally consume alcohol in fruits that ferment—a process that happens when yeast or certain bacteria are around to break down sugars in ripe fruit, creating small amounts of ethanol. Most animal species show signs of impairment or toxicity after consuming this substance at concentrations above 4 percent. But animal researcher Sofia Bouchebti, now at Ben-Gurion University of the Negev in Israel, suspected that hornets and wasps might tolerate alcohol better or even use it as a food source. After all, the guts of these insects are known to host yeast that converts fruit sugar to alcohol. When hornets or wasps pollinate and feed, some of this yeast is passed onto plants and their fruits—playing a key role in the fermentation process.
Bouchebti turned her attention to the hornet Vespa orientalis, a type of social wasp. For a study in the Proceedings of the National Academy of Sciences USA, she and her colleagues at Tel Aviv University fed both hornets and honeybees sugar solutions containing 0 to 80 percent ethanol that incorporated a trackable carbon isotope. The researchers found that hornets’ exhaled breath contained up to 300 percent more labeled carbon than the honeybees’, suggesting the hornets’ bodies broke down the alcohol that much faster.
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Hornets fed with 80 percent ethanol lived out their typical weeks-long lifespan; honeybees died within 24 hours.
“There’s lots of energy in ethanol, and it’s a great metabolic fuel,” says study co-author and zoologist Eran Levin. The problem for humans and many other animals, of course, is that there are behavior and health consequences as the substance interacts with the brain and organs. But when provided with nest-building materials, the ethanol-fed hornets in the study completed construction tasks as efficiently as sugar-fed ones. When faced with an intruder, they did not delay sending the usual “back off” signals. Moreover, hornets fed with 80 percent ethanol lived out their typical weeks-long lifespan; their honeybee counterparts died within 24 hours. Still, hornets showed no preference between sugar and ethanol when given a choice. “If ethanol is more nutritious and without bad effects, shouldn’t they want more? Maybe they can’t taste it,” Bouchebti suggests.
To distill the secret behind this metabolic mastery, study co-author and zoologist Dorothée Huchon led a hunt for genetic clues. She found that hornets possess multiple copies of the gene responsible for the enzyme that breaks down alcohol—an adaptation perhaps fueled by their relationship with yeast.
Three hornets feed on a ripe fig, which could provide naturally occurring ethanol.
Eran Levin
University of Rochester biologist James Fry says the hornets’ ethanol metabolism tells an “interesting evolutionary story.” But he cautions that the research methods are too different from those of other studies to directly compare ethanol resistance between species.
Robert Dudley, an insect flight specialist at the University of California, Berkeley, notes that the hornets would never encounter such high ethanol values in nature. Bouchebti says the researchers “aimed to find a maximum limit, and we still didn’t find it.”
Next up is examining gene expression during ethanol consumption and seeking patterns among animals known to be attracted to alcohol (some beetles and bats, for example). Dudley agrees: “A broader survey of social Hymenoptera and other insects is clearly called for.”