ELi5 Why can flys see you coming a mile off when you try to swat them…but they can never seem to find their way back out of an open door?
In: 415
They just don’t have much brain to work with. Dodging in a random direction when something big comes their way is dead simple. Figuring out what a door is might as well be rocket science.
Doors don’t exist in nature. They never evolved to have to understand and deal with doors. Things trying to kill them have always existed, and they had to evolve to stay alive.
This is also why the best way to swat a fly is not to approach slowly and then swat at the last second. The best approach is to quickly move in from across the room and swat with no hesitation. This doesn’t give the fly enough time to sense you and dodge in a random direction.
As others have said to a fly an open door, a window, a lightbulb, a TV that’s on, etc might all look very similar if the fly is just looking for daylight, making it very difficult to navigate an indoor space to find their way outside with such a tiny brain.
1. Flies don’t see why they should head out your door. They’re attracted to smells, and if there aren’t smells drawing them out they’re not going.
2. Flies can’t see very far. Like, a few meters at most, even though their eyesight is better than most insects (your average insect has a resolution like a computer screen from the 80s).
while they may “see you coming” it is actually more that they can sense it.
flies can feel your hand moving toward them by the rush of air it creates. this is the main reason fly swatters are perforated. Rolled up newspapers and magazines can work as well, as they do not act like a paddle pushing a wall of air toward the fly.