Kate Shaw, writing for Ars Technica:
Several plants, including species in the genuses Coffea and Citrus, produce nectar that contains caffeine; the concentration of caffeine in some of these flowers rivals that in a cup of instant coffee. We know what effects caffeine has on humans, but how does caffeinated nectar affect bees pollinating these plants?
It’s a fine line, though. Too much caffeine can kill insects.