How to Keep Flies Out of the House With Water Bags

Flies have compound eyes, designed to detect movement.

Many people believe that a clear freezer bag filled with water will keep flies away from the area where it is hanging, such as outside doors or near refuse bins. The common house fly has compound eyes, which contain up to 8,000 lenses each. These eyes are designed to detect movement, which is why flies are difficult to catch. Proponents of this remedy suggest that water in the clear bag reflects light in every direction. Flies are disturbed by the refracted light coming from the freezer bag and may also mistake it for a nest of hornets or wasps and leave the area.

Things You'll Need

• Sheet of reflective paper (tinsel)
• Four pennies (optional)
• Sharp scissors
• Piece of string (optional)

Instructions

1. Use a pair of sharp scissors to cut many small blocks from a sheet of reflective material. Place them on one side.

2. Fill a clear freezer bag with tap water and place the small blocks of reflective material on the water surface. Use the zipper mechanism to close the bag, or secure with a piece of string if the bag does not have a zipping lock.

3. Place pennies in the water as an alternative to reflective material. The light which reflects off either the tinsel material or the pennies adds to the overall effect and confuses the flies.

4. Hang the freezer bag near an outside door or window of your home.

5. Ensure that the bag is hung in a place where the lighting is good. Light refracts or bends as it passes through water, causing optical illusions. Flies, with their highly sensitive eyes, are bothered by this refracted light. The fly’s eyes provide the insect with a mosaic view of its surroundings and as it orients itself with the direction of sunlight, refracted light confuses it sufficiently for the insect to fly away.

6. Remove the bag and replace the water as needed. Hang a number of bags all around the building if you are experiencing a serious problem with flies. It may be necessary to hang bags over both the front and back doors as well as over open windows.

7. Discard old and algae-stained water and replace with fresh water as necessary. It is important that the water remains clean, so that all available light can be reflected from it.

References

• Ilovebacteria: Why Does a Bag of Water Keep Flies Away?
• Gardens Alive: Can Bags Full of Water Really Repel Flies?

Resources

• "The Arizona Republic"; Let's Focus on Flies' Eyes, Water Bags; Clay Thompson; May 2005