Amazing Honey Bee Vision
If you really want to stump non-beekeepers (and sometimes beekeepers), ask them how many eyes a bee has. They may be very surprised when you tell them the answer is five!
Bees have two different types of eyes - each with separate functions. There are three small eyes located in the center-top of a bee’s head called ocelli and they complement the two compound eyes located on the side of the bee’s head. These two sets of eyes process light differently and follow different pathways to the brain.
The name ocelli comes from the Latin word “ocellus” which means little eye and are sometimes referred to as “simple” eyes.
The ocelli are light-sensitive organs that cannot distinguish shapes like a normal eye because the refractive power of the lens is not sufficient to form an image. Two of the ocelli are directed left and right of the head while the central or median ocellus is directed to the front.
The single lenses help the bee maintain stability, orientation, navigate during flight and judge light direction. Using these ocelli, bees can gather light, and see ultra-violet and polarized light, helping them detect the ultra-violate colors that flowers emit. This ultra-violate light is not visible to humans.
Bees can detect polarized light because polarized light has vibrations within them that move in one direction. Polarized light is created when air molecules from the atmosphere scatter the photons to create a multilane highway designed for a high-speed traffic of light. Whereas unpolarized light has vibrations occurring at random angles without any specific direction.
The bee’s ocellus eyes, arranged in a triangle, can scan and match the polarization patterns in the sky and use the polarized light like a Global Positioning System (GPS) of navigation. Although the GPS uses an earth-bound receptor that triangulates with multiple GPS satellites, the honey bee’s ocellus eyes perform a similar function in reverse. Even when there is cloud cover and the sun isn’t visible, bees can use the polarized light to locate direction.
When bees return to the hive, they communicate the direction of the resource to the bees in the colony by using the information gathered by the polarized light. The bees also use this polarization information to travel to and from the hive. Basically, it’s a “bee road-map.”
Every bee has two large compound eyes. Each compound eye of the worker bee has 6,900 small lenses, known as facets. Drones have 8,600 facets in each eye. It is theorized that the drones have more facets allowing them to find virgin queens in the drone congregation areas. Each facet points toward a slightly different part of the visual field and this along with the curvature of the eye, allows them to see up to 280 degrees in their field of vision. By stretching your arms behind your back you can get an idea of the area of their field of vision. This explains why it’s very hard to sneak up on a bee.
The outer part of each facet, known as the ommatidia, is overlaid with a transparent cornea. The facet has a hexagonal face and when laid altogether they make up the surface of the compound eye. Although each facet collects a small part of the bee’s vision, once the visual signal reaches the brain those collective signals are converted into a mosaic-like picture. The image is similar to the picture produced by a television screen.
Each of the facets is connected to tubes with cells that respond to light. Four cells respond to yellow-green light, two to blue light and one reacts to ultraviolet light. A bee sees each individual flower and depending on the angle of observation the petals will appear to change color – known as iridescence. The color vision of bees is five times faster than humans and is the fastest known in the animal kingdom. The spectrum of ultraviolet light, which humans cannot see, is the most important to bees. The bees see illuminated shiny petals and associate this spectrum of UV with the availability of nectar. As the bee collects nectar, it also pollinates the flower and reestablishes the bee and plant symbiotic relationship that has lasted since the beginning of time.
During flight, bees have the ability to take the collection of images from the facets at a rate of 200 images/second and turn a blurred image into a sharp one. Humans have trouble converting these images at 30 images/second. Because of this higher flicker rate, bees can see individual flowers while in flight. Bees actually see moving flowers better than ones that are still. That's another reason it’s difficult to swat a flying bee!
Karl von Frisch, Nobel Prize-winner proved that bees can see color. When light shines on a flower, the light is reflected. Our eyes see the color that is reflected. Since bees have a broader range of color vision, including ultraviolet light, plants emit an ultraviolet light pattern in such a manner to form a target or “bulls-eye” to attract the bees to the nectar. This is known as “bee-vision”.
Bees have three photoreceptors (trichromatic) within their eyes. Although bees see ultraviolet, they can’t see red and can only distinguish shades of color between yellow, blue-green, blue, violet and ultraviolet. They don’t have a photoreceptor for red, so they can’t see the color red. Bees also see a combination of yellow and ultraviolet light known as “bee’s purple” – which humans cannot see. Based on scientistic studies the colors most likely to attract bees are blue, purple and violet.
A mother was watching her young daughter sitting in a patch of clover and trying to coax a honey bee to land on her hand. When she asked her daughter what she was doing the young girl replied, “trying to make my eyes beautiful.” When the mother asked how that was going to happen the girl replied, “You’ve always told me that - Beauty is in the eye of the beeholder.”