Flowers offer pollinators a sugary drink that sometimes comes with an unexpected trace of alcohol.
Nectar, the sweet liquid produced by flowering plants, is a staple food for hummingbirds, sunbirds, honeybees, and many other pollinators. These creatures can gulp down volumes equal to their own body weight in a single day. Scientists have known for years that sugary plant fluids can ferment when microbes move in, but until now, how much ethanol — the type of alcohol found in beer and wine — actually ends up in the nectar itself remained unclear.
To fill this gap, researchers collected 147 samples of nectar from 29 species of flowering plants growing at the University of California, Berkeley Botanical Garden. Using a sensitive enzymatic test, they found ethanol in 48 percent of all samples and in at least one sample from 26 of the 29 species. The concentrations were tiny: positive samples averaged just 0.016 percent by weight, with the highest single measurement reaching 0.056 percent.
The team, led by Aleksey Maro of the University of California, Berkeley, reports its findings in the journal Royal Society Open Science. “Our results indicate that exposure to low levels of ethanol among nectarivores is likely to be widespread,” the authors write.
The alcohol almost certainly comes from yeasts and other microbes that naturally colonize nectar and turn its sugars into ethanol. The researchers also spotted a modest link between higher sugar levels and slightly higher ethanol levels, hinting that the fermentation process may act as a subtle signal of nectar quality.
To understand what these trace amounts might mean for the animals that drink nectar, the team used existing data on daily energy needs and body sizes of hummingbirds, sunbirds, and honeybees. They calculated that the average daily ethanol intake for these pollinators works out to roughly the same dose a 70-kilogram person would get from drinking one standard alcoholic beverage spread across an entire day.
The authors also emphasized that the levels are far too low to cause intoxication. Hummingbirds and honeybees have already been shown in other work to tolerate much higher concentrations without obvious ill effects. Still, the daily exposure is not trivial for such small-bodied animals.
“Additional field and metabolic studies are needed to determine to what extent such ethanol concentrations are either physiologically or ecologically relevant for animal consumers,” the researchers note.
Citations
Aleksey Maro et al. Low-level ethanol is widespread within floral nectar. Royal Society Open Science. Published online March 25, 2026. DOI: 10.1098/rsos.250847
