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How Bees See Their World?

2013-04-12 01:45:50   作者:OK蜜蜂网   浏览次数:  评论:0 
摘要: Haveyoueverwonderedwhatthenaturalworldofmeadows,flowers,grassandtreesmustlooklikeseenthroughthefacetedcompoundeyesofahoneybeeorabumblebee?Dotheyseeincolor?Ifs...

Have you ever wondered what the natural world of meadows, flowers, grass and trees must look like seen through the faceted compound eyes of a honey bee or a bumblebee? Do they see in color? If so, what colors do they see and are they different from the portions of the spectrum that human eyes are tuned in on? Do they perceive motion the same as we do? Can they see colors or perceive visual attributes of objects to which we are blind?

If, like me, you have often wondered what it would like to be a "bee for a day" or just for a few minutes, then, this short narrative may begin to answer some of these intriguing questions for you. So, come join with us at The Bee Works and experience the alien vision sensory world of honey bees. Let's take that imaginary journey now and pretend to see the world through the unique eyes of a bee for just a few minutes...

Worker honey bees have eyes that are divided up into two great ellipses on opposite sides of their head. Each compound eye is made up of about 6,900 individual units/facets packed tightly together as hexagons and known as ommatidia. Each ommatidium is able to capture light rays from a small angle of view. These rays are focused by several lenses onto light sensitive pigment. Once stimulated, these sensory cells pass along nervous impulses coding information on the quality of the light (its wavelength = visible color and plane of polarization) to the optic nerves which eventually reach the optic lobes of the honey bees' brain.

How many eyes do you think a bee has? Two you say? No, actually, bees have five eyes in all. No, this isn't a trick question. On top of their head are three simple eyes, known as ocelli, arranged in a triangular pattern. These simple eyes with a single lens are best for informing the bee of changes in light intensity. These ocelli help them navigate around flowers and getting to and from the nest at dawn and dusk.

Honey bees are also extremely sensitive to rapid movements. This has been called their flicker fusion potential. To a bee flying at 15mph low over a flowering meadow, the flowers must twinkle on and off like stars in the night sky. The analogy is often made that if you put a bee in a theater, the moving film (going by at a mere 16 or 24 frames per second) would be seen as distinct still images by the bees. You would have to greatly speed up that same film to achieve the motion effect for a bee moviegoer. They also have other seemingly mysterious and certain alien visual abilities beyond our own. For example, bees can detect the plane of polarization of light in the sky. This allows them to detect the position of the sun even on an overcase day when there is only a patch of blue in the sky. That way, they can find their way to and from various patches of flowers and return back home safely without getting lost.

The color sense of honey bees (and other bees) was only guessed about until this century. Biologists since C.K. Sprengel (1793) had long believed that flowers acquired their colors as "living billboards" to advertise their presence to passerby insects who would, in turn, move their pollen grains from flower to flower--resulting in fruit and seed set for the flowering plants. Sprengel even called the markings on some colorful flowers "saftmale" (in German), sap signs in English to note that they were landing and orientation guides for flower-visiting insects. By being colorful, they thought, it would be easier for floral insect visitors to see the small flowers set against the green or brown backdrop of most environments. If bees and other insects could see and find them easily, that would allow them to move amongst the blossoms faster thus increasing their efficiency as pollinators.

In fact, honey bees were thought to be color blind until the pioneering experimental research of the late Dr. Karl von Frisch in Germany during the the early part of this century. He proved that they do in fact have three color (trichromatic) vision in many respects like our own visual syste123. Karl von Frisch was able to demonstrate that bees had color vision by training them to a little dish of scented sugar water (their sweet reward) set upon a blue square of paper. By randomly placing this blue square in a big "checker board" of gray squares, he could tell that the bees actually saw and recognized/learned where the blue square was positioned. They weren't just relying upon the relative intensity of the squares. This training technique has become the standard for many bee behavioral experiments up to the present day.

Although both honey bees and people have a visual system based upon three-colors, the limits of this color sensitivity are very different. People cannot see very far into the Violet or Ultraviolet region of the electromagnetic visual spectru123. We are essentially blind to wavelengths of light below 400 nanometers/millimicrons (light in this regions is called UV-A and UV-B light). These are the powerful light rays which cause us to tan or sunburn. Bees can see these invisible-to-us rays of light! Another interesting difference happens at the opposite end of the visible spectru123. We can easily see the color of a red sweater or red fire engine (at least many of them used to be red!). To a honey bee, however, the color red is invisible. They see red objects as black, or the absence of color. Share this with your friends at school, your teachers and parents. Did they know that bees are not colorblind and that they can see "secret" colors that we cannot?

 

In the photograph to the left we see an array of flowers as they appear to people who might be admiring them in a display case within a florist shop. Notice that they occur in many different shapes and sizes with various subtle color markings on their petals. The colors of flowers are said by physicists to be highly saturated. That makes them very noticeable when compared to other less-saturated colored objects in the natural environment. *These magnificient photographs appeary courtesy of Dr. Randolf Menzel (Berlin, Germany). See the reference to the publication where they appear below in the Suggested Readings section.

The collection of 10 photographs to the right show what the same flowers would look like to a passing honey bee. Notice that the photos are dark blue/black. These were taken by using a special ultraviolet-transmitting filter described below. Although we don't really know exactly how the bees eyes see the patterns (and their brains interpret these neurosignals) we do know that these hidden UV colors do stimulate the bees vision and tell them where to find the floral rewards (nectar and pollen) inside the flowers.

To see these same flowers as a bee would, we simply place a visible light-blocking filter over the camera lens (or VHS camcorder). This dark, almost black, UV filter only allows ultraviolet let to pass through. This is the opposite filter from a "skylight or haze" filter that many amateur photographers know about. Watch for an upcomming issue of GEARS in which we'll tell you how to take your own photographs of hidden UV floral patterns on certain flowers and butterflies for less than $50. Notice in the above UV photograph that the flowers look entirely different. Many flowers look dark (all UV absorbing) when viewed under ultraviolet light as a bee would see the123. Others (like some sunflowers or black-eyed Susans) have a characteristic central UV-absorbing bullseye pattern. Such flowers appear as what the insect physiologists have termed bee purple (the combination of yellow + UV). The outermost part of the sunflower ray petals reflect yellow light plus UV giving them this bees' purple color. We don't know exactly what thay color might look like to a hungry honey bee forager. The central portion absorbs UV so would simply be whatever color (brownish) is there alone.

There is much more to the story of how bee eyes work and how they perceive the colorful and varied natural and manmade world around the123. Go to your local school or public library and check out a book on honey bees. Try to discover for yourself some of the fascinating things that bee biologists, entomologists and botanists have found about the secret life of the bees and their world.

Suggested Readings--

⑴Frisch, Karl von. 1971. Bees: Their Vision, Chemical Senses, and Language. Revised Edition. Cornell University Press, Ithaca, New York, 157 pages. *Easy to read and understand account for anyone.

⑵Menzel, Randolf. 1990. Color Vision in Flower Visiting Insects. Institut Fur Neurobiologie Der Freien Universitat Berlin, pages 3-16. Prof. Dr. Randolf Menzel, Institut fur Neurobiologie der Freien Universitat Berline, Konigin-Luise-StraBe 28-30, 1,000 Berlin 33, Republic of Germany. *Technical article, may be difficult for students less than High School or College/University age.

⑶Menzel, R. and Backhaus, W. 1990. Color vision in insects: In: Vision and Visual dysfunction Vol. 6 (Ed. P. Gouras), chapter 15, MacMillan Press, Houndsville. *Again, a technical article, this one best suited for college-aged students.

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