Why flies hate these hanging bags?
Even though most insect repellants are based on emitting odors that bugs hate, the inspiration behind building this type of “fly frightener” has nothing to do with scent—for them, the repulsion is connected to their sight.
According to research compiled by How Stuff Works, entomologists agree that throwing a certain amount of shiny coins in a water-filled bag creates an inhospitable sight for flying insects. Just think of it as being the complete opposite of an oasis—once a fly spots the shiny coin and water combo, they’ll want to get as far away as possible.
What the insects are seeing in the bag is an example of light refraction, something the human eyes can handle, but for insect’s eyes, it’s a completely different story.
Let’s look at the common housefly, for instance. These pests are actually born with a pair of large “complex eyes” which contain 3,000 to 6,000 “simple eyes”. Experts liken their view of the world as being that of a mosaic pattern. Pretty cool, huh?
Since their sight is skewed, their sense of direction is tied to light sources, like the sun or a flame. When a housefly catches a glimpse of a contraption like the hanging water bag, they automatically get confused by the refraction, and they go on their merry ways.
From: Tiphero
