For some of the insects, a bright light source may be seen as an emergency beacon. These insects instinctively head towards light sources. Light, act as a familiar safety signal.
Another popular theory for attraction to light is that insects use it as a navigational aid. For example, an insect flying north, is able to judge its direction by keeping a natural source of light, such as the sun or moon. This method works well as long as the source of light remains both constant and at a distance.
If an insect encounters a round glowing portal light, however, it becomes confused by its source. This explains the strange behaviour of a moth continuously encircling a light source; it instinctively wants to keep the light on a certain side of its body while navigating its route.
The difference between insects that are attracted to light and those which are not, is a phenomenon known as phototaxis, a locomotory movement that occurs when a whole organism moves towards or away from a stimulus of light.
Certain insects, such as cockroaches or earthworms, have negative phototaxis, meaning they are repelled by an exposure to light. Moths, flies and many other flying insects have positive phototaxis and are naturally attracted to it.
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