Bitter-tasting caffeine primarily arose in plants as a toxic defense against herbivores like garden slugs. At high doses, caffeine can be toxic and repellent to pollinators.

However, at low concentrations, caffeine appears to have a secondary advantage, attracting honeybees and enhancing their long-term memory, said lead author Geraldine Wright, a neuroscientist at Newcastle University in England, whose study was published online March 7 in the journal Science.

"We show that caffeine—a compound whose ecological role is mainly to deter and poison herbivores—actually acts like a drug in an ecologically relevant context," Wright said. "The plant is secretly drugging the pollinator. It may help the bee, but the plant cares more about having a pollinator with high fidelity!"

Wright's team wanted to