Why are flys repelled by hanging bags of water up?

Question

This sounds riculous to me as a scientist but I have heard this too many times from too many sources to discount it...

Answer 1

This comes from the "How Stuff Works" site:

Some insist the flies perceive the clear liquid as the surface of a body of water. Others claim the insect flies away at the sight of its own magnified reflection.  But the most popular reasoning that pops up among entomologists... is simple light refraction.

Refraction takes place when a clear or opaque object, such as a piece of glass or a bag of water, alters the course & velocity of light. The rays of light, which normally travel in a straight line, bend. This effect is responsible for a number of optical illusions, such as mirages, that occasionally baffle humans as well. In theory, refraction can be just as confusing for some species of insect, especially the housefly. It boasts a highly sensitive array of eyes which allow it to see in multiple directions at once.

The insect's head mostly consists of a pair of large complex eyes, each of which is composed of 3,000 to 6,000 simple eyes. These eyes can't move or focus on objects like human eyes, but they provide the fly with a mosaic view of the world around them. Each simple eye provides one small piece of the puzzle, much like the way a screen's pixel delivers one detail of the larger picture.

A housefly bases its sense of direction on the direction sunlight comes from. Some entomologists believe that when these complex, sensitive eyes experience refracted light, the insect becomes confused and flies away.

http://animals.howstuffworks.com/animal-...

This method seems to need direct sunlight to increase the water bags' efficiency at repelling flies.  When the bags were tested  &  natural light conditions were NOT used... the bags had the opposite effect... the number of flies increased, instead of decreasing.

Interesting illustration showing how flying insects utilize "optic flow" sensors to maneuver through & steer clear of regions with dense obstacle fields. Optic flow refers to the apparent movement of texture in the visual field relative to the insect’s velocity.

http://www.pages.drexel.edu/~weg22/optic...

Here's a site that discusses how & why some people still cling to the belief that hanging bags of water repel flies. It brings up the idea that the reflection of the water disorients the flies & that the image the bags cast resembles spider webs, or another huge bug ( especially if you stick a penny inside the bag) :

http://ask.metafilter.com/19342/flies

Another discussion about using the hanging bags of water to repel flies:

http://www.boingboing.net/2008/04/15/wat...

Could it be that it works for some & not for others because of where it's placed... particularly, if the sun or bright light is actually reflecting on it & it's not just hung in a darkened spot? Seems like this needs to be checked out & I'd like to see more scientific tests done to know for sure if it's a myth ( as some say it is) or not.

This would make a great science project  :)

Answer 2

I don't have a clue

does this really work!

I'll find out myself!