Expert: Dana Krempels, Ph.D. - 12/11/2009

Question
Hi!
I was wondering how bees distinguish the color yellow (that does not have U.V elements in it?) and the color green?
Thank you very much
Yael

Answer
Dear Yael,

Bees have the very complex eye structure typical of arthropods, known as the compound eye.  The eye is composed of long, conical photoreceptor subunits, each known as an ommatidium.  You can get an excellent overview of the compound eye here:

http://users.rcn.com/jkimball.ma.ultranet/BiologyPages/C/CompoundEye.html

and see a nice diagram of an ommatidium here:

http://www.bio.miami.edu/dana/pix/ommatidium.jpga

Color vision in any animal is facilitated by the different pigments in the photoreceptors.  The more different classes of cones a vertebrate eye has, the more different colors can be perceived.  For example, the human retina has three different classes of cone, each maximally sensitive in the red, the green, and the blue region of the spectrum.  Incoming light will excite different proportions of the cones in the retina, and so different light stimuli will send different messages to the brain for processing and perception.  Hence, "color" is a psychophysical phenomenon:  something that happens in the brain; it is not a physical property of light itself.

Behavioral experiments done on honey bees in the early 1900s by Karl von Frisch and (later) Khun indicated that bees can distinguish between yellow, blue, blue-green, and ultraviolet.  They are color-blind with respect to longer wavelengths (red).  This suggests that honey bees have at least four different classes of color-vision conferring photoreceptor pigments.

But color perception and discrimination is also affected by the intensity of light, as you can see in the overview here:

http://www.springerlink.com/content/u8r16466810j860m/

A more recent study by Thery et al. (2004) suggests that bees may have even finer color discrimination capabilities than previously thought:

http://beheco.oxfordjournals.org/cgi/content/full/16/1/251

So to finally get to your question:  Bees apparently cannot distinguish yellow from green (in bees, the same visual pigment receives the wavelengths we distinguish as yellow or green via the action of *two* different cone pigments).  However, they do have a blue-sensitive pigment that appears to allow them to distinguish between yellow and and what we would call "blue-green".  

Hope that helps!

Dana