Why are flies attracted to light?

You don’t need to be a professional pest controller to know that insects such as flies are attracted to light. Think of all those times you’ve seen moths, beetles and other insects frantically flying around light fixtures and street lamps when it’s dark.

fly-cloth-closeup-blogYet a greater understanding of this natural attraction to light could help to develop more effective fly killers (insect light traps) and improve fly control solutions. Research into this topic is of vital importance to businesses in the food industry, like food processing and food retail even hospitality, helping them to avoid outbreaks of fly-borne diseases such as Salmonellosis, Dysentry and Gastroenteritis.

Rentokil’s Global Technical Centre has scientists investigating the physics of how light impacts the biological attraction of flies to a trap. This research has helped to uncover LED technology as a much more effective insect attractant than other conventional light sources.

When LED technology is combined with an effective fly killer unit, it offers the opportunity to capture and eliminate more flies than other conventional fly traps.

In fact, this research and the expertise of the technical team has helped Rentokil develop a new Lumnia fly control unit using LED technology to attract, eliminate and encapsulate flies effectively and hygienically.


What is it about the light from LEDs that is so attractive to flies?

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.

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 can 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 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.

Fly killers and LED technology

research-scientist-blogRentokil’s researches are able to prove the efficacy of the Lumnia LED fly control unit 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 fly control unit.

An effective fly control solution must also consider the correct placement of a fly unit, given what we know about phototaxis.

The placement of fly control units with respect to local light sources is of critical importance to their effectiveness.

This in-depth understanding of how light impacts the biological attraction of flies and other insects to a fly control unit demonstrates the complexity of pest control issues and the expertise, knowledge and experience required to successful control flies in a business premises.

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