Expert: Dana Krempels, Ph.D. - 10/23/2009

Question
QUESTION: Dear Expert

I have read that bees can see blue and ultraviolet but not red, which probably appears as black to them.

I have observed that bees are often attracted to yellow flowers.

How do scientists think bees see yellow?

ANSWER: Dear Margaret,

Because color is a psychophysical phenomenon, we cannot really predict how bees perceive what we call "yellow."  It may be perceived as something completely unlike the sensation we know as "yellow" but because we cannot get into their little bee brains to find out, we will never know.

Interestingly enough, there is also no way to know whether each human sees color exactly the same way.  It's not unlikely that there is variation, as the opsin portions of our photoreceptor pigments differ with our genes.  But because the sensation of color is something that is created in the brain and experienced as both a psychological and physical phenomenon, there is no way to compare between individals.  We're alive alone.  Just like the bees.

Hope that helps.

Dana

---------- FOLLOW-UP ----------

QUESTION: Thank you for your answer.

I realise that humans cannot know the actual experience of bees in colour vision in bees but wonder if the colour receptors involved in distinguishing yellow from other colours are similar to humans, or they distinguish the difference by another route (eg UV light or different means of colour distinguishing - I believe we have yellow blue distinguishing cones as well as red-green - or if there is something other than colour that makes them go for yellow flowers. They are particularly the yellow oxalis type variety known as "soursobs" in Australia. This was introduced as a garden flower but has become a weed.

Answer
Dear Margaret,

Ah, sorry I misunderstood your question.  

The arthropod eye is completely different from that of a vertebrate, and the photoreceptors evolved independently (along with their pigments).  Rather than being constructed like a camera, as our eyes are, the bee (and other arthropod) eye is constructed of many long, conical subunits called ommatidia. An excellent overview can be seen here:

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

with a close up of the ommatidium:

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

As you can read here, bees have several different visual pigments, each sensitive to a different region of the spectrum (544 nm or "green", 436 nm or "blue" and 344 nm or ultraviolet).  This enables them to distinguish between blues, yellows, and possibly green, but not in the red region of the spectrum (about 580nm and longer).

Human primates have three different classes of cones, each class sensitive to either red, blue or green.  The proportions of each type of cone excited by a particular light stimulus will determine the perceived color, and this is essentially the same mechanism as in the bee, though the colors are not the same.

You can read a bit more here:

http://www.sewanee.edu/Chem/Chem&Art/Detail_Pages/ColorProjects_2003/Crone/index

and another interesting interpretation of how bees might see colors here:

http://www.monash.edu.au/news/monashmemo/stories/20070523/bee.html

Hope that helps.

Dana