[Odonata-l] insect vision and polarized light

[John and Sue Gregoire <khmo@att.net>]

Below is an exchange found on the Cayuga Birds listserv. Thought the members of this community would find it interesting as well, and the authors gave me the OK to pass it on to you. Please forgive my clumsy cut and pasting.

Sue G.

Subject: Polarized light
From: Meena Haribal <mmh3 at cornell.edu>
Date: Sat, 22 Mar 2008 13:51:53 -0400
X-Message-Number: 5



I had studied Polarization of lights in my Physics class looong time ago 
and as an organic chemist I know most of the natural chemicals have 
property of polarizing incident light in one particular direction. In fact 
in most of natural compounds left handedness seem to be most common.  In 
fact one isomer which rotates light in one particular direction is most 
active than the other or the mixture of two even as drugs.

But, I was interested in knowing how they perceive and what kind of 
information their brains process! Of course it is hard to understand what 
birds or beasts are thinking.   But I did some BIOSIS and web search, here 
I came across this website 
http://polarization.com/index-net/index.html  which explains how polarized 
lights are used by insects. This is quite a fascinating website. Anyone 
interested in polarized light should see this.

From: Geo Kloppel <geokloppel at clarityconnect.com>
Date: Sat, 22 Mar 2008 08:00:23 -0400
X-Message-Number: 2

Meena wrote:

>> Also, recently this question of why see polarized lights are  
>> important.  Birds and insects have capacity to perceive polarized  
>> light. So how is that helpful them and why dont we see?

Insect vision ought to be less susceptible to the blinding glare from  
a planar source (such as a window pane), because the tubular facets  
(ommatidia) radiate from the interior of the compound eye, pointing  
in many directions. Only one facet at a time should capture the  
glare, or for that matter gaze at the sun or the moon or a bright  
star. A simple night-navigation routine for an insect brain might  
read something like "keep the moon in ommatidium # L-9355".  I don't  
know what benefit accrues from being able to detect polarized light,  
but, just by the nature of the information that polarization conveys,  
I would expect it to be related to navigation or some kind of  
orientation-response.

-Geo



--
John & Sue Gregoire 
Field Ornithologists 
Kestrel Haven Avian Migration 
Observatory 
5373 Fitzgerald Road 
Burdett, NY 14818-9626 
"Conserve & Create HABITAT" 
http://home.att.net/~kestrelhaven/ 
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