insects light

Why are insects attracted to light?

It doesn’t take 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 out. But – unlike a pest control professional – you probably haven’t considered why, and how a greater understanding of this natural phenomenon can help to develop more effective fly killers (insect light traps).

Whilst it may not be of direct interest to consumers, extensive research into this topic has been undertaken to support food businesses such as food processing and food retail, to help ensure consumer food safety, and avoid outbreaks of fly-borne diseases such as Salmonellosis.

The team of scientists at Rentokil’s Global Research and Development Centre has looked into understanding the physics of how light impacts the biological attraction of flies to a trap. This research has helped uncover LED technology as an insect attractant far superior to conventional light sources.

insect light control

Why are flies attracted to light?

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, act as a familiar safety signal; just as air bubbles lead the way to the surface of the water for some underwater 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 a round 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.

Why are flies attracted to LED?

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. More than that, LED technology also emits light in a different way and produces UV-A as intense beams of light, which penetrate further into the surrounding space than light phosphor lamps, for example.

LED fly killer inofgraphic

House flies, in particular, can see and are attracted to UV light, which humans cannot see. Because we can’t see UV light, we don’t use it in our buildings and our environment. This means that any UV light that is used in urban buildings light up like a beacon, making UV light traps incredibly effective: they stand out in the human environment as the brightest source of UV-A light.

Fly killing efficacy

Rentokil’s researches are able to prove the efficacy of fly killers using LED technology through a standard Half-Life measure test. The Half-life measure represents the time taken to eliminate 50% of flies released in a test chamber. The lower the Half-life measure, the more effective the insect light trap.

An effective fly control programme, however, must also consider the correct placement of fly trap units (given what we know about phototaxis). The position of fly killer units with respect to local light sources is of critical importance to fly control effectiveness. All this insight – and more – has been distilled into Rentokil’s leading fly control service solutions. Speak to an expert today to find out more.

Jack Lyons

I joined the Marketing and Innovation team at Rentokil in 2015, and my mind has quickly become accustomed to the weird and wonderful world of pests. Outside of work my main hobby is music, being a huge fan of bands such as Queen and Led Zeppelin as well as being an avid drummer.


  1. Pest Control Reply to Pest

    What a great question to ask. I’m intrigued to see how science will progress pest control in the future! It seems that we still have so much to learn about our planet. Every day turns over a new leaf, and there’s a different bug to fix under every one! Cheers!

  2. You gave some great reasons for hiring a pest control service. It seems that a professional would have the training to determine the best way to exterminate pests from my house. You brought up how it can be difficult to know the right dosage and chemicals for getting rid of pests, so leaving those details to a professional would be a good idea.

    I like that you mention keeping your house clean because that is going to really help. If the rodents don’t have a nest that they can make and everything is picked up, you won’t ever have to worry about rodent issues. It would also be smart to have a pest control company come out to check for rodents if you have seen them.

  3. Excellent contribution to the importance of light in pest control. In a related way, I also see a relation between phototaxis and this research. The work has some relevance to the origin and survival in organisms that display either positive or negative phototaxis. Keep up the productive research

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