Can a Bag of Water Keep Flies Away?



Perhaps you’ve visited a restaurant and seen clear, water-filled bags cinched up in the outdoor dining area. It turns out that the hanging bags are all about driving pests away. The water bag method of fly repellent is all a matter of light. Refraction takes place when a clear 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. For a common housefly, things get very confusing. Because flies have a highly sensitive array of eyes that allow them to see in multiple directions at once, they provide a mosaic view of the world around them. These eyes can’t move or focus on objects like human eyes do. Each simple eye provides one small piece of the puzzle, much the same way a screen’s pixel delivers one detail of a larger picture. A fly bases its sense of direction on the direction sunlight comes from. When they spot the water-filled bags, they become confused and fly away. So, the next time you have an outdoor party and don’t want to be bothered by flies, try hanging up some water-filled bags and you’ll have your very own “fly free zone.”