I don't think it does. There is speculation about the refraction of light, but I think this bag business is like making something up and telling someone if you carry a walnut in your pocket it keeps bears away. I've carried a walnut for a week now have have seen no bears. If you have a house infested with flies and use the water bag thing then tell others if it works.

The water bags do drive houseflies away. Houseflies, being highly defenseless, are nervous types and don't like to sit still when they see something moving nearby, because it could be a predator. The water bag acts like a lens in which the movements of people in the area are reflected. Even if the fly is too far from the action to see it directly, it can see a shifting of light and dark in the water bag, which it interprets as nearby movement, and it will fly away from the bag. The reason it doesn't work on any other insects is that the other insects don't have as highly developed ocular senses. I have used this bag o' water trick in two different locations which were inundated with flies and can testify that it does work, and there is scientific reasoning that can be used to collaborate. The walnut in the pocket argument is highly specious with no grounds at all, and a very poor example to use in conjunction with the water bag.

1) "I found it very informative. I wanted to let you know about a fly repellent that is is very effective. A plastic bag filled with water and hung will repel flies from the area. I learned this trick while living in the Ozark mountains where the fly problem was horrible. I saw these bags over every front door and on every patio. Supposedly the fly can see his reflection in the bag and does not like it. I am not sure how true that part of it is, but for whatever reason, the bags really work." Source: http://eartheasy.com/inside_the_envelope.htm 2) "Fly repellents Zip-lock water bags Many people swear that a zip-lock bag filled half-way with water and attached over entry-ways will repel flies. No one yet knows how or why it works, but there is speculation that it has something to do with the way the moving water refracts light. If you have tried this please use the tips form at the bottom of the page to share your results with the rest of us." Source and further information: http://www.howtogetridofstuff.com/pest-control/how-to-get-rid-of-flies On this page there are reports from several people who have tries this solution. Sometimes it worked. sometimes not. Maybe it depends of the kind of flies, or the region.

Try the CD's hung on a string.. Many in Rich neighborhoods like April Sound Property Owners Association does it on Lake Conroe,Tx

I have recently gone back to a restaurant that previously had annoying number of flies around even when there were window screens installed. I was surprised about numerous hanging plastic bags half filled with water around the entire restaurants where the windows were located. When I confronted the waiter to say what weird cheap decorations the owner decided to install in the restaurant, he answered that these bags were supposed to repel flies. He added the owner read this in the internet. Lo and behold, I was surprised that not one fly bothered us or was present in the restaurant the entire 1 hour we were there. I noticed that screens were not present anymore on all the windows. I have read articles in the internet that have debunked this method. I can see why ziplocks don't work as effectively as the plastic bags I saw hanging in this restaurant. The plastic bag one choses must be very clear much like cellophane like. I suppose this increases the light refraction. Ziplock type plastic are more opaque than clear. This distinction must matter a lot from my experience in this restaurant.

Hi: I remember when I was in college working on my degree in Biology, I was given a choice as to creating new life with flies or making a disease resistant to an antibotic. Of course I choose to make a disease resistant to an antibootic, but I also studied the creation of new life with the flies and its larve. Needless to say, I still have some information on that subject in the form of a research article and I believe that after reading this article, then you will be enlightened to create your own theories on this subject of: How does a plastic bag filled with water act as a fly repellent. What does the fly really see? Jul 1, 2003 By: Dr. Moray Anderson Pest Management Professional Customers are always coming up with questions about pests that could stump even your most knowledgeable technician. Flies are a popular subject, because they are usually quite visible at an account. For example, have you ever been asked how the eye of the fly "traps" light? Light is captured in the eyes of insects by structures called ommatidia. Each adult housefly, for example, has about 3,000 ommatidia in each eye. The outermost section of them can be seen in the eyes of the housefly as hexagonal patterns. In each of these 3,000 ommatidia, there are eight sensory cells (R1-R8). Each contains photopigment, which responds to particular wavelengths of light. In most insects, the regions of the cells that contain the photopigments are fused - and all the cells sample the same point of light. However, in flies there is a remarkable and unique modification. Each of the light trapping zones in the sensory cells is separated from its immediate neighbors. The clever trick is that light from any point is collected by six different ommatidia, and therefore the intensity of the image on the retina is greatly enhanced. This makes the vision of the flies much more sophisticated than that of almost any other insect. Response to UV light Flies' eyes are also very special in their response to ultraviolet light. The sensory cells mentioned above (R1 to R8) each have different sensitivities to the various parts of the color spectrum. Cells R1 to R6 are particularly sensitive to UV light. These cells have a secondary and unique photopigment that reacts to the light in the UV range (300 to 400 nm). Within the eyes of flies, there are a couple other unique features: Girl goggles - In male flies, there is a special zone in the front of the eye (the two eyes have their greatest area of binocular overlap here) where the cells have lost their ability to see color. These spots are specially developed so that the males can detect female flies in flight in the immediate vicinity. Polarized light detection - This ability is concentrated in certain zones of the eye, particularly around the margins. The cells that are sensitive to polarized light are also highly sensitive to UV light, and are thought to be navigational aids. These physiological processes only reveal what the fly's eye is able to detect. It is possible to show by electrical recordings what regions of the eye are sensitive to what wavelengths. It is only by elaborate and detailed behavioral experiments that we are able to get clues as to what the fly sees. The brain of the fly is highly evolved to processing visual information, with about 70% devoted to visual processing. Each fly species has different visual sensitivity that changes according to the sex of the fly, its age, its feeding status, its reproductive stage, etc. Not only will this knowledge dazzle your customers, it can be helpful when explaining how effective your insect light trap can be at the account. Dr. Moray Anderson is technical director of the Killgerm Group, West Yorkshire, UK, and is considered an expert in public health as it relates to flying pests. Contact him at pccontributor@advanstar.com

How Stupid...hang anything from your porch and when the wind blows it,and it moves ,flies will bug off.Hell put some gravel in a Wal-Mart sack and tie it to your porch and when it moves from the wind I'll bet cha dont see any flies!!ppffttt.My neighbors have several bags of water hanging from their porch that they swear by and we have only a wind spinner...no flies at either place..Could it be its November? Or that when anything moves it scares flies...humm..guess well have to go back to the ghetto to talk with whom ever thought this up!Water in a bag as a fly repellant..shhesh!