Can bees see ultraviolet?

What the shift means

Bees are trichromatic like us, but the three receptors sit at different wavelengths. The consequence is not that bees see extra colours on top of ours; it is that the window has moved. They gain ultraviolet at one end and lose red at the other, and a pure red flower reads as dark unless it also reflects ultraviolet or blue.

The shift also produces a colour we cannot imagine. Ultraviolet and yellow together stimulate the bee's receptors in a combination with no human equivalent, conventionally called bee purple. It is a real perceptual category for the animal.

Nectar guides

Many flowers carry patterns produced by ultraviolet-absorbing pigments: bullseyes, radiating lines, darkened centres. A plain yellow silverweed or evening primrose photographed under ultraviolet shows a dark heart and a pale rim that is invisible to us and unmistakable to a bee. The markings steer an arriving bee to the nectary, which shortens the visit and makes pollen transfer more reliable — a benefit to the plant rather than to the bee.