Although we are both visual creatures, the world that bees see is completely different to ours. So, how do our worlds compare?
ONE HUMAN LENS vs MANY INSECT LENSES
Just like an old-school camera, the human eye is made up of one lens with a surface to capture the image on. When we look at an object the lens focuses the light that comes from the object onto the back of our eye – onto the retina. Light sensitive receptors on the retina send an electrical signal to the brain. Our brain receives these signals plus the signals that have come from our other eye. It combines them and we “see” the object.
Insects, including bees, have a different set-up. They have compound eyes. A compound eye is made up of thousands of tiny individual lenses. The eye of a honeybee worker has almost 6,000 lenses. Based on the principles of the human eye, we might think that the honeybee would see 6,000 images of an object. But, just as in the human brain, the bee brain combines all these signals. It produces a composite image from these 6,000 snapshots. A bit like a digital camera and its pixels, the more lenses the more detailed the image. The honeybee queen who flies just a few times in her life, and so doesn't need to see very well, has only 3,500. A male honeybee, who must chase a queen to mate with her on the wing, has 10,000 lenses per eye – all the better to see her with!
A pixelated view of the world might look something like this:
WE SEE RED vs BEES SEE PURPLE
Humans and bees are trichromatic – our perception of colour is based on a combination of three colours. In humans these colours are red, blue and green. The human eye has receptors for all three but there is a part of the eye that is particularly rich in red receptors. It has green receptors too but no blue receptors at all. This is the Fovea (see it marked on the human eye diagram above). The image that comes through our eye falls on this spot. Our vision is sharpest here. Red/green is the colour of ripe fruit amongst green leaves. Red is for lipstick and warning signs - we are alert to it.
A bee’s colour receptors are ultraviolet, blue and green. They can see reddish wavelengths such as yellow/orange but because bees don’t have a red receptor as such, they can’t "see" red light. The colour we see so vividly is, quite literally, unseen by bees. Bees see blue-green, blue, violet and “bee purple”. Bee purple is a combination of yellow and ultraviolet.
This is where bees’ inter-relationship with flowers comes in. Flowers rarely reflect one colour of light and many reflect ultraviolet light. Flowers that may seem very similar to us are easily distinguished by bees on the basis of colour e.g oil seed rape and field mustard. Petals can also have visual patterns that are clearly seen by bees but which may be hard for humans to see at all. Nectar guides are an example of these often “hidden” patterns. They point the insect to the centre of the flower. The bee gets the reward of nectar that it is after – and the flower gets pollinated.
The most likely flower colours to attract bees are purple, violet and blue. The red flowers that are so striking to us are probably just “black” to bees - unless the flower reflects some ultraviolet. We can't know what bees really see but their inability to see red is useful to consider if you want to plant for these pollinators.
Watch this amazing video which shows the same flowers though the eyes of humans and bees. It also shows the butterfly’s eye view – another important group of pollinators that see the world very differently to us.
PATTERNS IN THE SKY
And finally, bees have a type of light perception we lack completely. They are able to see polarised light.
Light from the sun vibrates in all directions. Passing through the earth’s atmosphere makes it vibrates in one direction – it has become polarised. As a result, the sky has a visual pattern. The pattern begins at the sun and extends out across the sky. Unlike humans, bees can see this pattern. Because the pattern originates from the sun, it has a direction. The bees can navigate using it, even on cloudy days. The worker bees out in the fields collecting nectar use this perception and their inbuilt sense of time to find their way home to their colony.
It's impossible for us to experience the world the way a bee does. But it’s fascinating to imagine the pixelated, purple and patterned world they inhabit.
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Thanks to:
Photograph of Wool Carder bee - Gilles San Martin on Flickr via a Creative Commons Licence
Diagram of the Human Eye and Insect Vision vs Human Vision - Insect Vision at Ask a Biologist - Arizona State University
Diagram of a Bee Compound Eye and the spectrum showing Bee Vision vs Human Vision - Sharla Riddle "How Bees See and Why It Matters" in Bee Culture Magazine
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