Re: Why are different insects attracted to different light intensities?

Hi Taryn:

Different species of insect do not see the same wavelengths of light, so two insects can behave quite differently to the same light. For a good introduction to light (and a link at the top that goes to yet another introduction) have a look at this article from our archives. Also, have a look at this article on vision in insects.

Scientists still only have a vague notion of how different types of insects can see; that's because it's pretty hard to figure out. It was big news in the scientific world a few years ago when someone noticed that plants have patterns that only reflect ultraviolet light (and we can't see). They wondered why plants would have such patterns, and went looking at the vision of some pollinating insects. Sure enough, those insects could see in the ultraviolet at the same wavelenth that the plants were reflecting in and could thus home in on those plants.

So, we know that the wavelenghts in the visible spectrum that insects can see varies. We also know that how "well" an insect can see at each wavelength varies. We can then expect that different insects to behave quite differently.

As an example, lets do a quick thought experiment. Imagine an insect that can only see in the red end of the visible spectrum, but not in the blue; and another insect that can only see in the blue, but not in the red. Let's also assume that both insects tend to be attracted to light (scientists call that behaviour phototaxis). Now imagine we take both of these insects and put them in a room with a blue light. The insect that can only see in the blue will be able to see the light, and will be attracted to it - it will fly, crawl, swim, whatever in the direction of the light. The insect that can see only in the red, however, will not even know that the blue light is there! In this case you'd expect the red-seeing insect to not be effected by the light at all.

Of course, in the real world things are much more complicated- light generally has a complex spectral composition, and vision by insects is similarly complex. Nevertheless, I hope the above example illustrates to you how different lights and visual ability by insects can influence their behaviour. There are a few web pages that mention this topic, which you can access by checking out this search at google.com.

Hope that helps!
Rob Campbell, MAD Scientist