How bees find flowers

What a bee sees

Bee colour vision is shifted towards the short wavelengths. They see ultraviolet, blue and green, and they do not see red as a colour — a red flower reads as dark unless it also reflects ultraviolet. This is why bee-pollinated flowers are so often blue, violet, yellow and white, and why red flowers are usually bird-pollinated.

Many flowers carry nectar guides — patterns visible only in ultraviolet that direct a visitor to the centre. A plain yellow flower to human eyes may carry a bullseye in ultraviolet that is unmistakable to a bee.

Scent, and how fast bees learn it

Scent carries further than colour and is what a bee uses to locate a patch at a distance. Honey bees learn a floral scent extremely quickly — a single rewarded encounter is often enough to establish an association that lasts days.

This is also how recruitment works inside the hive. A dancing forager carries the scent of the flowers she visited, and recruits leaving the hive are searching for that scent as well as flying the indicated bearing.

The electric field

Flowers carry a small negative electric charge and a flying bee carries a positive one. Bumblebees have been shown to detect the resulting field and to distinguish flowers by their field patterns, and the detection appears to be through movement of body hairs.

The field also changes after a visit, because the bee's positive charge alters it. That gives a subsequent visitor information about whether a flower has recently been emptied — which is useful to both parties, since the plant does not benefit from a visitor arriving at a flower with nothing left.

Flower constancy

An individual bee tends to work one plant species at a time, ignoring others even when they are equally rewarding and closer. This behaviour is called flower constancy, and it is the reason monofloral honey exists at all.

It benefits the plant enormously, since pollen delivered to another species is wasted. The usual explanation for the bee's side is handling efficiency: learning to work one flower shape well is faster than switching between several.

What makes a flower worth visiting

• Sugar concentration in the nectar. Bees prefer higher concentrations and will abandon a dilute source.
• Nectar volume and how fast it refills.
• Accessibility. A deep corolla excludes a short-tongued bee entirely.
• Distance. A closer patch of equal quality wins.
• Handling time. A flower that takes a long time to work is worth less per minute.