Flies are one of the most common and annoying pests that can invade our homes. Food, trash, and other organic matter can attract these creatures, carry disease, and contaminate our surfaces. They are also very difficult creatures to catch, as they have very fast reaction times and a good sense of movement.
But despite their agility and speed, flies often have trouble finding their way out of a confined space. You may have noticed that flies buzz around a closed window and poke their heads at the glass, even if there is an open window right next to it. Why are they doing this? Are they stupid, blind, or just stubborn?
First we need to understand: How do houseflies see colors and polarization?
Unlike humans, who have three types of color receptors (red, green, and blue) in their eyes, flies have only two color receptors (blue and green) in their eyes. This means that they cannot distinguish certain colors such as yellow and white. But they can see ultraviolet light, which humans cannot.
Ultraviolet light is often used by flowers to attract pollen and by other insects to communicate with each other. Flies use ultraviolet vision to locate food sources and avoid predators that may camouflage themselves in visible light.
Another feature of fly vision that humans lack is the ability to detect polarized light. Polarized light is light that vibrates in a specific direction, such as sunlight reflecting off water or glass.
Flies can sense the polarization angle and use it to navigate and orient themselves. For example, they can use polarized light to find water sources or avoid flying into spider webs.
Let’s come to our question, why do flies keep their heads on the glass?
Despite their advanced vision systems, flies have some limitations, making them vulnerable to windows. One of these limits is the lack of depth perception. Since their eyes are fixed on their heads and cannot move independently, they cannot judge distances very well.
To estimate how far away something is, they rely on motion parallax, the marked change in position of an object as it passes by. However, this method is not very accurate when the object is close or stationary.
Another limitation is that they cannot adjust focus or pupil size. Unlike human eyes, which have a single deformable lens and a pupil that can expand or contract to control the amount of light entering the eye, fly eyes have fixed lenses and no pupils.
This means that they cannot adapt to different lighting conditions or focus on different objects. They can only see clearly at a certain distance and brightness level.
These limitations are; makes it difficult for houseflies to perceive windows as solid barriers. They can confuse them with open spaces or water sources due to the reflection and polarization of light.
Because their depth perception and focus are poor, they may not notice the window frame or the open window next to it. As a result, they may keep crashing into glass or flying along the edge of the window until they exhaust themselves or find another way out.
There are some simple things you can do if you want to help the flies get out of your house without harming you or yourself.
The first option is to cover the window with a dark cloth or paper, which will block the light and reduce the interest of the flies.
Another option is to open another window or door on the opposite side of the room, creating a diagonal breeze that will direct the flies towards the exit. You can also try using a soft vacuum cleaner or a soft brush to gently trap and release any flies outside.
Flies are actually not as stupid as they seem. They have an extraordinary vision system that enables them to survive in a complex and dynamic environment. However, their vision also has some disadvantages that make them susceptible to being stuck in windows.
By understanding how houseflies see the world and why they behave the way they do, we can appreciate their fascinating biology and coexist more peacefully with them.
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