Hooked on citrus
Have you noticed that bees often go mad for citrus flowers? This is because bees, like humans, can get hooked on caffeine!
Several varieties of citrus plants have toxic concentrations of caffeine in their leaves and other tissues, as well as low concentrations (similar to that in weak coffee) in the nectar itself.
Naturally caffeine-laced nectar in some plants enhances the learning process for bees, which means they are more likely to return to those flowers.