• Michael Zawadzki

Why are insects attracted to light?

You don’t have to be a pest control professional to know that insects are attracted to light. Just think of all those times you’ve seen moths and other insects frantically flying into or around light fixtures when it’s dark.

As homeowners, we have been convinced for a number of years now that LED lights are a smarter, more energy efficient way to light our homes. It seems this light source may also be highly attractive to insects.

The way light is emitted from LEDs is the reason they are particularly attractive to certain insects. LEDs produce UV-A as intense beams of light, which penetrate further into the surrounding space than light phosphor lamps, for example.

House flies are particularly attracted to UV-A as their eyes are sensitive to light at that wavelength.

Light attraction for flies 

There is no single scientific explanation as to why flies are attracted to light. There are several theories which offer a possible explanation, as outlined below:

Using light for safety 

For some insects, a bright light source may be seen as an emergency beacon.

When in doubt, these insects instinctively head towards light sources, which are generally positioned on higher ground than the hazardous environment they are currently in.

Light, for some insects, acts as a familiar safety signal, just as air bubbles leading the way to the water surface might help for other creatures.

Using light for navigation 

Another popular theory for attraction to light is that insects use it as a navigational aid.

An insect flying north, for example, is able to judge its direction by keeping a natural source of light, such as the sun or moon, on its right. This method works well as long as the source of light remains both constant and at a distance.

If an insect encounters around incandescent porch light, however, it becomes confused by its source. This explains the peculiar behaviour of a moth continuously encircling a light source – it instinctively wants to keep the light on a certain side of its body whilst navigating its route.

Phototaxis – an attraction to light 

The difference between insects that are attracted to light and those which are not is a phenomenon known as phototaxis.

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.

Debating science 

There is some debate in the scientific community over why a positively phototactic insect, like a fly, will continue to hover around an artificial light source even when natural light becomes available.

Some believe that the insect is not attracted to the light itself, but the darkness surrounding it.

Others suggest the insect’s eyes, which often contain multiple lenses, struggle to adjust from light to dark, leaving the insect vulnerable to predators whilst night-blind. In this case, the insect may find it safer to remain in the light rather than fly away and become too blind to react to threats and obstacles.