A garden filled with beautiful flowers always attracts our attention, but stunning flowers didn’t evolve to attract human eyes. The role of showy flowers, in most cases, is to attract pollinating insects: bees, butterflies, hoverflies, etc. Plants produce the flower colors we find so pretty in order to seduce insects. But most of the time, what bees see is not exactly what people see.
The color vision of human beings is actually excellent and we can distinguish some 10 million different shades, more than most other mammals. However, our vision is limited to red, orange, yellow, green, cyan, blue and purple rays, that is, rays between about 400 and 780 nanometers (nm) in length. In particular, we can’t distinguish ultraviolet rays (less than 400 nm).
Bees, on the other hand, see mostly rays between 300 and 560 nm in length and therefore see ultraviolet rays that we can’t. However, they can’t see red rays that, to us, seem highly visible. For a bee (and most other insects), a perfectly red flower will appear black. And for us, any part of a flower that is strongly ultraviolet will look black.
It’s possible, by means of specialized photographic equipment, to approximate what bees see in a flower … and the result is fascinating!
In particular, many flowers we see as having with uniform colors are marked with ultraviolet lines called nectar guides that direct the insects towards the center of the flower where their reward, either nectar or pollen, is concentrated … and where the flower wants to see them go to pick up the pollen that they will then deposit on another flower of the same species.
Also, the iridescent spots that we see as black at the base of poppy petals are actually ultraviolet in color. This explains why bees visit even red poppy flowers, a color that bees aren’t supposed to see*.
*In fact, a flower that seems red to us might still include other colorsthat bees can distinguish. They don’t necessarily see all red flowers as entirely black.
When Birds See Red
If insects can’t see red, birds certainly can. In fact, birds in general not only see a wider range of color than humans and insects, but can distinguish more shades of color than we can. Many flowers have taken advantage of this by adopting red shades that insects ignore, but that birds love. This allows them to choose birds as their exclusive pollinators and to skip insects entirely. After all, while many insects are good pollinators, others steal pollen and nectar without doing any pollinating at all. Thus, most pure red flowers in the wild are designed to be pollinated exclusively by birds.
Hence the common belief that hummingbirds, the epitome of pollinating birds, prefer red flowers. In fact, hummingbirds love flowers of all colors, but are usually the only creatures in their environment to frequent red ones.
If someone invents glasses that will allow us to see our gardens as bees and butterflies do, let me know: I would love to see my plantings as a bee would, even if it is only for a few minutes.