This question originally appeared on Quora.
Answer by Matan Shelomi, entomologist:
Mosquitoes fly at about two kilometers per hour (1.2 mph), which sounds slow, but at their size, it's like you flying over 100 times that! They are going blindingly fast for something that small.
You can't catch them for a few reasons. One, they see you coming. Their eyes are big and round and multifaceted, so they are quite capable of seeing above and behind themselves. You can't sneak up on a mosquito easily.
Second is your hand moves slower than they fly and has more distance to cover. The mosquito doesn't need to move far to get away from your face, while your big and slow hand has to travel all the way to your head.
Lastly, the mosquito makes decisions faster than you. When you decide to hit one, a signal goes from your brain to your spinal cord to your arm muscles to start the hand in motion. The time it takes is the length from your head to your back to your arm divided by the speed of light (which is close enough to speed of electricity in a nerve), so about a few nanoseconds. That sounds impressive, but once the mosquito sees motion, a signal from its brain goes to its nerve cord to its wing muscles, and the time ends up being about a hundredth of a nanosecond. They think and act 100 times faster than you can. Your hand never really had a chance!
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