Who knew that the flower nectar of citrus plants — including some varieties of grapefruit, lemon and oranges — contains caffeine? As does the nectar of coffee plant flowers.
And when honeybees feed on caffeine-containing nectar, it turns out, the caffeine buzz seems to improve their memories — or their motivations for going back for more.
"It is surprising," says Geraldine Wright at Newcastle University in the the U.K., the lead researcher of a new honeybee study published in the journal Science.
In order to study the effects of caffeine on bees, Wright and her colleagues trained the bees, Pavlovian style, to associate a reward of food with a smell of a flower.
"It's a little bit like Pavlov's dog," explains Phil Stevenson of the Royal Botanic Garden in Kew, outside London. "When Pavlov rang the bell, the dog salivated. And in this case, when the bee detects the smell, it extends its proboscis," Stevenson says. (The proboscis is the bee's long, hairy tongue used to suck up the nectar from the flower.)
The researchers wanted to know whether the bees would respond differently to flowers that contained a caffeinated nectar, compared to those that just had sugary nectar.
And, wow, turns out there was quite a difference. The bees feeding on the caffeinated nectar were three times better able to remember the flowers' odor 24 hours later, Stevenson says.
So could this mean that a caffeinated bee has a better memory? "That's exactly what the study shows," he says.
"They [the caffeinated bees] just didn't forget," says Wright.
And the benefit of remembering? Wright says these bees may have an advantage over their pollinating competitors in terms of locating food.
So, whether the caffeine is improving bees' memories — as these researchers suggest — or simply making bees more motivated or vigilant to seek out more of the stimulant, it's intriguing that caffeine could be giving bees the same kinds of buzz that people get.
"Caffeine absolutely influences our behavior," says Abraham Palmer of the University of Chicago. "It changes mood and performance in a variety of different ways." Due to genetic differences, our individual responses to caffeine vary.
Some of the best studies on the effects of caffeine on people come from the U.S. military, where caffeine has been studied as a way to keep soldiers alert.
In one study, researchers observed the effects of caffeine on a group of sailors who were training to become Navy Seals.
During one portion of that training, they are substantially sleep deprived and exposed to a variety of other stressors, "including cold temperatures and demanding physical activities," explains researcher Harris Lieberman of the U.S. Army Research Institute of Environmental Medicine in Natick, Mass.
When Lieberman studied the behaviors of sailors who consumed caffeine compared to those who had a noncaffeinated placebo, he documented a range of benefits.
"We found that in moderate doses, caffeine enhanced ability to pay attention, and it enhanced vigilance," says Lieberman.
And caffeine also seemed to improve the exhausted sailors' short-term memories, something Lieberman was not expecting to see. "We were surprised that caffeine had such widespread effects," he says.
But in the absence of exhaustion, caffeine doesn't seem to help people remember any better.
"I don't think we have good data that establishes that caffeine has beneficial effects on memory," Lieberman says — at least among people who are well rested.