Re: Do insects see in color?

Hello Deran, how are you?

This is a fascinating question, and recent research is still leading us 
further into a new level of understanding of not just insect behavior, but 
of flowering plants, and of the interaction between the two. Sir David 
Attenborough's "The Private Life of Plants" makes for very good and 
accessible reading material on this topic.

The range of colours that we call visible light is basically a small slice 
of the electromagnetic spectrum with frequencies around 6 x 10^14 Hz. The 
colour red occupies the lowest frequency of visible light, and violet 
occupies the highest. This is the spectrum of visible light TO HUMAN 
EYES.. 

Insect eyes come in two forms, simple and compound. Simple eyes do very 
little more than differentiate between light and dark. Most adult insects 
have 3, Caterpillars may have 6, but these organs do not enjoy the 
sophistication of our own. The compound eye - the classic insect eye that 
everybody imagines, is a different matter altogether.

It is made up of many tiny segments called ommatidia and is capable of 
seeing in perfect full colour. However, the spectrum of light that is 
detected seems displaced to a slightly higher range of frequencies; that 
is to say that an insect's red-end vision is very poor, but they do see a 
range of colours well up into what we call 'ultra violet'. Humans can only 
guess as to what these colours might look like, but with modern frequency 
attenuating and filtration techniques, we can interpret them visibly and 
suddenly the world looks very different. Flower petals are decorated with 
intricate patterns highlighting their reproductive areas and the adjacent 
sources of nectar for visiting insects. Even the most apparently drab 
butterflies display hugely sophisticated patterns. We are yet only 
beginning to research the significance of this invisible world that 
insects enjoy. Both the Flies and the Cockroaches that you study have 
compound eye structures.

Here is an experiment to prove the colour vision of insects. Take two 
pieces of coloured paper, one true yellow, and one blue (if you look at 
RGB values on your PC, true yellow is 255,255,0 and blue is 0,0,255). Try 
to ensure that the papers are not aromatic at all. Don't colour them with 
a solvent based paint because insects have highly developed senses of 
smell and it will effect your results. Take your two pieces of paper and 
leave them outside in an area that is frequented by small flies and midges 
(usually anywhere you're about to have a barbeque in the summer) you 
should find that the yellow is much more attractive to them. Night-flying 
insects, by contrast, find blue, violet, and ultra violet much more 
alluring. Place a fluorescent tube light on a white sheet at night and 
watch the moths and beetles.

Cockroaches generally shun light, but if you do experiment with them, be 
particularly careful how you set up your experiment as their instinct to 
follow the aroma of food will probably override anything else and a 
cockroach's definition of what is edible is quite surprising. I have heard 
of several species eat soap, shoe polish, and all manner of unmentionable 
things. Yummy.

Enjoy
Justin Roux