First: Bees can sense which flowers are “open for business” based on their electric fields. Although animals have been known to be able to detect electric fields, this is a first for an insect.
The way this works is that when a bee flies through it bumps into charged dust particles in the air, which cause it to be stripped of electrons thus gaining positive charge. Flowers on the other hand have negative charge.
This charge difference, however small, not only makes pollens jump from the flower to the bee, but it also helps the bee figure out which flower it should visit. The higher the voltage difference between the flower and the bee, the more the chances that the bee will find nectar in the flower
Second: Flowers attract bees by giving them a dose of caffeine.
Just like in humans, caffeine stimulates the bees. But what’s more is that researchers found caffeine also helps bees long-term memory retention. Thus the nectar of flowers that is laced with caffeine is remembered better by the bee.
It’s a win-win for both. Bees get more nectar and the flower gets to spread more of its pollens.
Bees + electric field: Clarke et al. Science (2013)http://dx.doi.org/10.1126/science.1230883
Bees + caffeine: Wright et al. Science (2013)http://dx.doi.org/10.1126/science.1228806
Ed Yong in Not Exactly Rocket Science
Kate Shaw in Ars Technica
Image credit: Ars Technica