Why Is It So Hard to Hit a Fly?

(Last Updated On: July 19, 2022)

Every now and then you get jumped by a little buzzy fiend while you’re trying to work or do anything really. The only thing worse than finding a bug is losing the bug, so now your entire day has shifted to killing whatever bug has decided to take residence in your abode. Sometimes, you can just smash them with a flip flop. Others you can maybe even get them in your fist. But everyone has chased a housefly around for an almost embarrassingly long amount of time (right?). So, what makes it so hard to hit a fly?

Frames Per Second

You probably only hear this term in the context of slow-motion cameras or when you’re trying to purchase a new computer monitor. Obviously, your brain and eyes don’t operate the exact same way as a camera shutter, and neither do the eyes of a fly. 

However, it does let us conceptualize the way we perceive motion. Our eyes just send our brains a bunch of static images and our brains string them together to tell us “this thing is moving.” When you’re talking about screens or cameras, this is expressed in frames per second (how many images are shown per second). Most movies are at 24 FPS, and the average human captures information between 30 and 60 FPS. The upper limit is a little higher, though it’s a little more limited. A study in 2015 found people could detect flickers on a screen with refresh rates between 50 and 90 Hz. 1 Hz is functionally equal to 1 frame per second, since Hz is a measure of how frequently a screen updates (how many times per second it can change the image it is displaying). When shown a panel of LEDs, people could detect signs of flickering at 500 Hz

This is where house flies come in. Their eyes can perceive motion in the ballpark of 300 FPS. Functionally, time passes much slower for a fly than it does for a person, it’s like having slow motion cameras for eyes. If it makes you feel any better, the compound eye of a fly is absolutely terrible at capturing image quality.

Reaction Speed

Ever done that test where someone drops a ruler and you have to catch it? Maybe you felt pretty good when you found out your reaction speed was pretty fast. Human reaction speeds average between 220 and 380 milliseconds. A fly can go from grounded to takeoff in 7 milliseconds, with the upper limit being 14 milliseconds. Their reaction speed is between 30 and 50 milliseconds, and is among the fastest in the insect kingdom

Within 100 milliseconds, a fly can do a lot. It can perceive you, identify that you are a threat, figure out where it has to go to avoid you, and then take off–well before you’ve really figured out it’s time to swat at it.  It doesn’t help that compound eyes give the fly almost 360 degree vision–so it’s not like you’ll be sneaking up on it. 

See if you know some other bugs here. Maybe you’ll have a better time swatting at them.



About Kyler 706 Articles
Kyler is a content writer at Sporcle living in Seattle, and is currently studying at the University of Washington School of Law. He's been writing for Sporcle since 2019; sometimes the blog is an excellent platform to answer random personal questions he has about the world. Most of his free time is spent drinking black coffee like water.