How do bees choose their flowers?

Sensing the electric charge of flowers allows the bee to decide which ones to visit and which to avoid.

Why bees detect electric charge

Flowers that have been recently visited have depleted levels of nectar and pollen. Such flowers, having reduced resources, aren't the optimal choice for bees to visit. 

When bees fly, they develop a positive charge. (This is due to friction with air particles.) 

Meanwhile, flowers usually have a negative charge. So when bees land on a flower, some of its positive charge transfers to the flower. 

Thus sensing the flower's electric charge allows a bee to effectively decide which flowers to avoid and which to land on.

How bees detect electric charge

Bees are covered in filiform hairs. These react to electric charge.

Unvisited flowers retain a negative charge. The bee's positively charged filiform hairs bend towards these flowers (opposites attract).

Visited flowers have some positive charge. As such, the bee's filiform hairs get deflected (likes repel).

As only flowers with depleted resources have a positive charge, a bee detecting their electric field enables them to pick resource-rich flowers. 

This is why bees hover in front of a flower before landing or moving on: to process the signals from its filiform hairs.