Science reveals that we're too slow to swat flies because of their eyes

Science reveals that we're too slow to swat flies because of their eyes

You've seen it in the movies. A young kid sits cross-legged, and tries repeatedly to smack a fly with his bare hands. He fails, and fails. The fly buzzes about his head and irritates him. Finally, after all his trials and tribulation, his master raises his utensil from the bowl he's been eating from, and grabs the fly from the air between two wooden chopsticks.

What gives, then? Why is it so difficult just to swat a tiny, pesky fly out of the air? Well, the reason, as usual, is biological science.

The passing of time may be real, but our experience of time is subjective. We see the world as a continuous flow, but in reality, images are constantly being updated between the eyes and the brain. Our vision is pieced together by a series of flashes. Every second, humans undergo 60 flashes, or snapshots, quite literally the 'frame-rate' of our lived experience.

Turtles only average 15 flashes per second. What this means is that turtles experience time 1/4 as rapidly as human beings. So all that slow walking? To them, it feels just right. That's their experience of time. What about flies? Well, flies experience a staggering 250 flashes per second.

The frame-rate of our visual-brain communications, or the "flicker fusion rate", tends to be much higher for smaller animals. Flies, being so tiny, have us utterly beat. The fastest flies ever recorded have 400 flashes per second, which would make them wildly faster than we are. When we try to swat them, they can literally see it coming many times faster than we can see our own hand moving toward them. In slow motion, that makes the hand rather easy for a fly to dodge.

So, if flies are so fast, then how does anyone catch them? Well, birds are also way faster than we are. I'm sure you've realized, if you've ever tried to catch a bird, that they're extremely quick. The pied flycatcher, a small bird that eats flies, experiences 146 flashes per second. That's nowhere near the fly, but it's still over twice as fast as a human. If you could move twice as fast as you do now, you'd find it far easier to catch a fly, wouldn't you?

It's crazy how subjective time really is, depending on how your brain and vision is wired. Flies, with such small heads, have virtually no response delay between their eyes and their brains. Signals are transmitted so fast they hardly have to travel at all. That gives them an enormous advantage, and results in more speed. But the speed is all relative, tied to how an organism experiences time.

It's only due to powerful cameras, that can see 1,000 flashes per second, that we can even break down the precise motions of flies in the first place. Our technology is our final trump card over natural selection, it seems.

So just remember, the next time you catch a fly, that you're moving way slower than you think you are. Best to use a swatter, for increased range. Even if the fly can see you, it still has to dodge. So a newspaper, for example, has a lot better chance of hitting the fly than a tiny hand.