Coffee buzz: Honey bees are caffeine fiends

© David W Cerny
Like people, honey bees can get hooked on caffeine. Plants trick the flying pollinators into changing their natural behaviors so they can get more of the drug, a new study has found. Bees even become more hyperactive after sipping caffeine-laced nectar.

Caffeine is a natural secondary compound found in the roots and leaves of some plants ‒ like coffee and citrus, for instance. It’s normally a protective measure, as the bitter taste is a turnoff for herbivores. But it’s also found in the sweet and appetizing nectar of those plants’ flowers, as a way to trick honey bees into repeatedly visiting them, researchers found in a study published Thursday in the Cell Press journal Current Biology.

Dr. Margaret Couvillon of the University of Sussex led a team of researchers that tested bees’ responses to a sucrose solution with field-realistic doses of caffeine or without. They found that bees would rather drink caffeinated nectar than food of an equal quality that didn’t contain the drug. As a result, plants may add caffeine to their nectar to attract bees while providing substandard forage, the group said in a statement.

“These new findings are a reminder that, while mutually dependent, the interests of plants and pollinators don’t always align,” Couvillon said. “Some plants, through the action of a secondary compound like caffeine that is present in nectar, may be tricking the honey bee by securing loyal and faithful foraging and recruitment behaviors, perhaps without providing the best quality forage." 

The caffeine caused the insects to forage for food more, returning to those caffeine-laced plants, even after the well had run dry, so to speak, and making them less likely to search out other food sources. They also did their special “waggle dance” ‒ a unique behavioral technique used to recruit other bees to the same site ‒ four times more often. The quadrupling of the waggle dance turned each bee recruited into a caffeine fiend as well, strengthening the effect, the group found.

"If a bee goes to a caffeinated plant, it's still getting nectar ‒ it's getting a reward, so it's not a complete and total disaster," Couvillon the Washington Post.

And the caffeine had a long-term effect on the bees, too.

"We saw that if they just had one, three-hour exposure to the caffeinated nectar on the first day, they would come back [to the empty feeder] for many more days, and more often within each day," Couvillon told the Post. "If they've had caffeine, they're less likely to check the surrounding area. They're really hooked on that location."

And the drugged-out bees lower the efficiency of the entire colony. When they ignore non-caffeinated plants, they’re foraging suboptimally by not taking full advantage of potential food sources.

"I think when people think about pollination, they think of the collaborative nature of it, the nice, sweet partnership of it," Couvillon said. "But as with many partnerships, there’s potential for conflict. One side will always want to cheat the other if they could get away with it."

Instead of looking for other sources of nectar, the bees wasted four or five days searching for the caffeine buzz when the source ran out, she told New Scientist. “They were kind of desperate,” she said, saying they became “exploited pollinators,” meaning “the plants are tricking them into foraging in ways that benefit the plant, not the bee.”

All's not lost for the plucky pollinators, though. James Nieh of the University of California in San Diego told New Scientist that bees have some tricks up their sleeves, too.

“Although it may seem that the poor bees are being tempted or drugged by these plants, bees have their own tricks that the plants need to defend against,” he said.

He pointed out that bees will gnaw their way through the base of the flower to get nectar, leaving pollen intact and allowing them to get the nectar from long flowers that they couldn’t normally reach into. And, over time, the relationships between plants and pollinators will co-evolve, preventing cheaters from prospering too much.

“Nature is not big on honesty unless it’s somehow enforced,” Nieh said. “It’s kind of an arms race.”