Environment

  • Issue 115 / January-February 2017



    The World through the Eyes of Honeybees

    Aidan Yielding

    The earth and the sky are filled with “light,” which are really colors of countless different wavelengths. Different colors are visible or invisible to the naked eye. When we say “visible,” we usually mean, “visible to the human eye.” However, certain kinds of light that are invisible to humans are visible to other species. In spite of living in the same world, all creatures see and perceive different worlds.


    One kind of light that is mostly invisible to the human eye is polarized light, which comes from sunlight reflecting off brilliant surfaces. Polarized light spoils our clarity of vision on sunny days. It appears as flashes on the sea or an asphalt road. In order shield our eyes from this light, we use sunglasses. We need to do this even though the naked human eye only perceives a very small amount of the polarized light on earth. However, this is not a shortcoming. On the contrary, it’s a blessing to us. If we were better able to perceive polarized light, we would not see any object clearly, owing to the dazzling lights around us.


    As evidenced by polarized light, the human eye is actually quite limited. Just as it cannot see radio or television waves, it cannot see ultra-violet light either. Since ultraviolet light is harmful to the retina of a human eye, it is prevented from reaching the retina by the eye’s external structures.


    Every animal has a different ability and threshold when it comes to seeing colors. For example, honeybees have three-color vision, just like humans do. In the human eye, there are three types of conical cells that perceive wavelengths in red, green, and blue. All other colors are perceived as mixtures of these three colors, albeit in different proportions.


    Just as there are colors like green or red, ultraviolet light has a color of its own. We do not name the color, for we cannot see it, but ultraviolet color exists for many other creatures. Since it is a very dense and brilliant form of purple, other colors would be more distinct and difficult to perceive if humans could see ultraviolet.


    Bees have very complex eye structures including comb-shaped units made of cells that perceive ultraviolet color. These cells are necessary for bees to be able to see ultraviolet light, because they locate their own position and the direction they will fly according to the existing position of the sun. They use ultraviolet light to find their hives or flowers with nectar. In experiments, researchers observed that when another source of light was used instead of sunlight, bees were unable to find the direction of their hive. Even on a cloudy day, it is easy to perceive ultraviolet light. Thus, bees can locate the position of the sun and then find the direction and place of flowers containing honey. Surely, the colors and patterns of flowers appear differently to bees than they do to humans.


    Honeybees also see polarized light. They use it to determine the exact location of the sun at any given moment. However, as polarized light might dazzle the eyes and reduce clarity of vision, the eye cells of honey bees are placed at the back and upper part of the eye’s structures. Since a honey bee does not see polarized light with the lower part of its eye, it is not dazzled by such flashes and reflections. It uses the upper and back portions of the eye to see polarized light, and can thus to determine which direction to fly. This trait is not unique to bees; for instance, hummingbirds, which feed on flower nectar, also perceive ultraviolet light.


    Bees’ eyes are surrounded by a dense layer of tiny hairs, which help them to navigate in windy weather. These tiny hairs have nerve extensions within them. They sense the slightest hint of wind, sending the relevant information to their brain and pointing them in the right direction.


    As mentioned above, a honeybee’s eye is a very complex structure. It is a unified form of more than 8,000 hexagonal and simple eye units. Each of these simpler units has its own lens, crystal, and sight cells. This united (or combed) eye system enables a honeybee to perfectly perceive the slightest movement that occurs around it. While the human eye can only see movement across 180 degrees, a bee’s eye will recognize the slightest movement across 360 degrees. Thus, it can notice every kind of possible danger and take protective action.


    A honeybee sees moving objects better than unmoving ones. Therefore, honeybees are more likely to visit flowers shaking in the wind. For this same reason they are more likely to attack people running away or moving their arms or legs. Honeybees see moving objects better than stationary ones because their vision is very blurry, at least relative to human eyesight. They see objects with 1/60th the clarity of human vision. In other words, an object we comfortably recognize from a twenty-meter distance, a bee must be as close as 30 cm to recognize. Thus, honeybees see the whole world virtually like a honeycomb. For example, they see a human face in a fragmented and blurred way, as if looking at it from behind a milk-glass.


    Bees are supposed to harvest honey from flowers, and the sight system they possess is exactly as needed for this purpose. Conversely, the human eye consists of a single cornea and lens system. For this reason, humans see an unmoving spot much more clearly and smoothly. While we cannot detect flower nectar from afar, humans are endowed with the ability to behold and appreciate the beauty of a flower. And this is what we are meant to do.

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