We know that flies can perceive changes in the world around them up to seven times faster than a human - we appear slow to them.

I'm wondering how this is possible. Is it just that information travelling is limited by the speed of light, and it has a shorter distance to travel across a flies brain? Or is there some metabolic or other biological reason for this?

(It would be great to speed up a human's brain - but I'm sure there are a million reasons why that is not possible).

My question is: Is the reason that flies can perceive things faster because their brains are smaller?

  • $\begingroup$ If we assume fly neurons are like human neurons, they probably conduct a signal at about 100 m/s. If we assume a fly brain is about 600 uM wide, it takes about 6 microseconds to send a message from 1 side to the other. Assuming a human brain is 15 cm across, it takes about 1.5 ms to get across. These are very quick estimates based on limited data, but assuming all things equal, the fly brain's tiny size would make some things faster. $\endgroup$
    – user137
    Aug 5, 2016 at 11:29
  • $\begingroup$ Cool - could there be any other reason? $\endgroup$
    – hawkeye
    Aug 5, 2016 at 11:32
  • $\begingroup$ I should add, there is a difference between transmission speed and decision making speed. The fly needs to make a decision whether or not it will fly away from a threat. Simply because it has a shorter distance to move signals around in its brain, it does not necessarily mean it's faster at decision making. Although there would be tremendous selective pressure for flies to decide as quickly as possible and escape potential danger. $\endgroup$
    – user137
    Aug 5, 2016 at 11:32
  • $\begingroup$ They have complex eyes and can see too well. Some responses are just reflex. It is not really about decision making. $\endgroup$
    Aug 5, 2016 at 11:53
  • $\begingroup$ @WYSIWYG I guess decision making could include reflexes in a very broad sense of the phrase. Flies probably don't have much conscience thought, so reflexes could make up a lot of their behavior. It would be interesting to see how much of their tiny brains are dedicated to visual processing. $\endgroup$
    – user137
    Aug 5, 2016 at 13:09

1 Answer 1


Fly neurons aren't like human neurons. They have different nerves that transport signals faster than human nerves. So they can see your hand moving towards them faster than we can see for ourselves, which makes them able to avoid being squashed (most of the time).

  • $\begingroup$ That's interesting that flies would have neurons that transmit action potentials more quickly than human neurons. Is there a source to cite for it? $\endgroup$
    – user137
    Aug 5, 2016 at 14:37
  • $\begingroup$ That's fascinating - have you got a reference? $\endgroup$
    – hawkeye
    Aug 6, 2016 at 4:18
  • $\begingroup$ I remembered this from my entomology class. I can't find the reference right away but I'll try to find it and post it here! $\endgroup$
    – Kasper
    Aug 8, 2016 at 6:39

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