Even plants which have adapted to the threat they pose can suffer from extremely high levels of pollen theft, according to the study.
Dr Mario Vallejo-Marin, an evolutionary biologist at the University of Stirling and senior author of the study, said: "It's a co-evolutionary arms race between plants and bees. Some plants have fortified structures called anthers, where pollen is locked up behind a thick wall. The only way to open these 'pollen vaults' is through small pores at the tips.