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| Earth on Oct 21, 2012

Why are moths attracted to flame?

Moths – and many other flying insects – are probably more disoriented by a close light source than they are attracted to it.

You might have heard the saying “like a moth to a flame” to describe a fatal attraction. But why are moths attracted to flame?

Photo credit: beinggreen

The fact is scientists think moths aren’t so much attracted to the light of a flame or other bright light as they are disoriented by it. Here’s how it works. Like many flying insects, moths are able to find their way partly by using light as a compass. When the source of light is the sun or moon, that light source is very distant, and the incoming light rays that strike the insect arrive just about parallel to each other.

So moths – and many other flying insects – have evolved to expect to receive light at a fixed part of the eye. As long as the moth flies more or less in a straight line, this visual pattern remains unchanged.

Now consider what happens when the light source is a nearby candle. Then the angle at which the light strikes the moth’s eye quickly changes while the moth holds to a straight-line course. The moth tries to do what it has evolved to do under the light of the sun or moon – that is, maintain a constant angle to the source.

And as it does so, it spirals in toward the light.

So the moth seems “attracted” to the light – so much so that it might end up drawn into the flame.