Does Time Fly for Flies? And Why Are They So Hard to Swat?

by | Feb 28, 2018


There is no way to tell for sure how various species perceive time or even how different individuals within the same species perceive time. Does time seemingly pass as the same speed right now for me and my 15-year old daughter sitting next to me? However, there is evidence that time appears much slower for flies as compared to humans. (Related IFOD on time seeming to pass faster as we age): Why does time seem to pass faster as we age?

How fast various species perceive time seems to be correlated to their Critical Flicker Fusion Rate (CFF rate).  An animal’s CFF rate is the lowest speed at which flickering light appears to be a constant unflickering source. Thus, CFF rate is a measure of how fast an animal’s eyes can refresh and process information.

Human’s CFF rate is about 60 times per second, dog’s CFF is 80 per second,* turtles are much slower at about 15 times per second. Flies have a very fast CFF rate of 250 times per second or more!

It appears having a fast CFF rate provides an animal or insect the ability to faster react to threats or opportunities. This is why it is so hard to swat a fly: time likely appears to move much slower for a fly. A fly swatter or shoe that appears to us to be moving quickly probably appears to be moving much slower to a fly.

Studies of various species suggest that smaller animals with higher metabolic rates  generally have higher CFF rates. Birds and other flying animals also tend to have high CFF rates as being able to process images at high speeds is important. It appears that evolution pushes animals to see the world in the slowest motion possible.

*Until recently, TVs had a refresh rate at 60 hertz, which is right about at the human CFF rate. Dogs, with their higher CFF rate, would have seen the images on the TV as rapidly changing still pictures, not as a continuous stream as we do (it would be more like watching a strobe light). Over the past 5 years or so most new TVs have a refresh rate of 120 hertz or higher. So, dogs might be more likely to watch modern TVs than those of the past.



  1. Great story. As an aside, a couple of decades ago a student did a study of how flies move in response to a threat, like a fly swatter. The student found that the fly moves upward within about 15 degrees of straight up. To test this, I tried clapping my hands directly above flies where they sat. I found that I trapped them with remarkable regularity. Try it sometime… but wear gloves.

    • That is fascinating. I will try it. How far above worked best?


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