What Do Bees See? And How Do We Know?
I was reading a children’s book about insects to my daughter recently, and it said that bees see colors differently than humans do. My daughter immediately asked, in short succession: “What colors do they see? Why? How do we know?” I did some homework to find out, and discovered that bees see flowers much differently than we do. If anything, they are more beautiful.
Humans see light in wavelengths from approximately 390 to 750 nanometers (nm). These wavelengths represent the spectrum of colors we can see. Bees, like many insects, see from approximately 300 to 650 nm. That means they can’t see the color red, but they can see in the ultraviolet spectrum (which humans cannot). Bees can also easily distinguish between dark and light – making them very good at seeing edges. This helps them identify different shapes, though they can have trouble distinguishing between similar shapes that have smooth lines – such as circles and ovals.
Vision is important to bees, because they feed on nectar and pollen – and that means they have to find flowers. Bees can use odor cues to hone in on a flower, but that only works when they’re already pretty close. Vision is essential to help the bees find flowers at a distance.
While it is possible that bee vision has evolved to become attuned to flowers, it is more likely that flowers have evolved to attract insect pollinators – including bees. Flowering plants rely heavily on insects to transmit pollen from one flower to another, allowing them to reproduce. As a result, many flowers have distinctive ultraviolet color patterns that are invisible to the human eye, but are incredibly eye-catching to bees.
For example, these ultraviolet patterns often outline “landing zones” for bees, pointing them towards the part of the plant containing nectar and pollen. That’s good news for the bees, of course, but it also makes it more likely that some of the flower’s pollen will stick to a bee and be inadvertently deposited in another flower.
How do we know what bees can see? For one thing, there is a long history of behavior experiments based on training bees to respond to specific colors. Essentially, researchers would put out bee feeders (containing sugar water) along with different colored targets – such as a yellow one. The bees would learn to associate the yellow target with the food, and would keep coming to the yellow target even after the food source was removed. The bees did this even when multiple other targets were in place that were various shades of grey. If the bees couldn’t see yellow, some of them would have explored the grey targets.
We also know what bees can see because researchers have looked at the actual photoreceptors in the bees’ eyes. Specifically, researchers have exposed bees to different wavelengths of light to determine when these photoreceptors fire off signals to the brain. If there’s no response to a specific wavelength, it means it didn’t register to the photoreceptors.
You are now prepared to wow your kids if they bring this question up.
Also, for those interested, an impressive collection of ultraviolet flower images is available here.
Note: Many thanks to Michael Simone-Finstrom, a postdoctoral researcher in NC State’s apiculture program, for taking the time to talk to me about bees. Any errors in the above post are mine and mine alone.