How do bees choose which flowers to visit?

What a bee is actually reading

• Colour, in a spectrum shifted from ours. Bees see ultraviolet, blue and green, and cannot see red as a distinct colour. Red flowers are usually signalling to birds; where bees visit them, they are following ultraviolet patterns we cannot see.
• Nectar guides. Many flowers carry ultraviolet markings that point at the reward like a landing strip. Photographed under UV, a plain yellow flower frequently turns out to have a bullseye in the middle.
• Scent, learned and remembered. Bees associate specific floral scents with reward and can be trained to them, which is the basis of a good deal of experimental work.
• Shape and handling time. A flower a bee can work quickly beats one it has to wrestle with, which is why a dense spike or a flat composite head outperforms scattered single blooms.
• Electric fields. Flowers carry a weak negative charge and a flying bee a positive one; bumblebees can detect the resulting field and use it to tell a recently visited flower from an unvisited one.

Flower constancy, and why it matters

A honey bee forager on a given trip works one species and largely ignores others, even when better forage is available nearby. From the bee's point of view this is efficient — she has learned to handle that flower and switching costs time. From the plant's point of view it is the whole reason bees are worth paying: pollen delivered to another flower of the same species is pollination, and pollen delivered to a different species is wasted.

Constancy also explains why monofloral honey exists at all. Bees cannot be confined to one plant, but they behave as though they were within a trip, and if a landscape is dominated by one flowering species the crop comes back overwhelmingly from it.

Where choice is not really choice