Have you ever been to a food market and seen stallholders with a see-through plastic bag of water hanging over their food displays? Or seen houses with old compact disks (CD's) hanging in the windows, and wondered "what are those actually for?" Wonder no more... They are hanging there because some people think that shiny, reflective surfaces (such as the water in a plastic bag and CD's) can keep flies away.
So we thought that since its nearly fly season (summer!) we'd look at whether this is fact or fiction.
Can reflective, shiny surfaces really keep flies away? The short answer is sort-of, in the short term. This is because both plastic bags of water and compact discs reflect and refract light.
Light reflection and refraction:
Reflection is when light bounces off an object. Smooth, shiny surfaces reflect light at the same angle that it hits the surface.
Refraction is when a clear or opaque object, such as a piece of glass or a bag of water, alters the course and velocity of light. The rays of light, which normally travel in a straight line, bend. This effect is responsible for some optical illusions such as mirages.
Reflection and refraction are thought to be just confusing for some species of insect, especially the housefly. (You can read more about the different types of flies here.) This is because flies have 4000 lenses in each eye. These lenses allow them to see in multiple directions at once and make them very sensitive to detecting movement.
These lenses can't move or focus on objects like human eyes, but they provide the fly with a mosaic view of the world. Some entomologists suggest that when the fly's complex eyes experience refracted light from a reflective surface, the insect becomes confused and flies away.
The key thing to note is that they are only temporarily disoriented. Eventually, flies will find another flight path to get past the confusing light and then - ultimately - they'll still land on your food.
So, to sum it up: whilst reflective surfaces may temporarily discourage some flies, this is not a foolproof solution to getting rid of flies.
How to keep flies away for good:
While water bags and CD's serve to deter flies, electric fly control units work the opposite way around. An electric fly control unit, such as Rentokil's Lumnia unit, attracts flies to the LED lights within the unit and then traps and kills flying insects in a safe and discreet manner.
We also believe that fly control should be holistic, so proofing and denying flies access to breeding locations are also important as part of an overall fly control strategy. Rentokil offers an external fly bait box that effectively prevents flies breeding in areas such as refuse or waste areas.