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Why We Can’t Swat Flies

By Shlomo Maital

Jeff Goldblum in the cult movie The Fly

   After 66 blogs on COVID-19, it’s time for a break.   Let’s talk about something more pleasant – like, flies. And, how come we are not able to swat them?

   The answer to this crucial troubling question was found by Prof. Shannon Olsson and doctoral student Pavan Kumar Kaushik at the Tata Institute of Fundamental Research in Bengaluru, India, with Marian Renz at Universität Bielefeld, Germany. They have just published their results in Proceedings of the National Academy of Sciences.

 “It took five years to design a VR world for the apple fly,” Shannon confides, “because first one has to nail down how the insect views the world. There’s little point in testing its skills if we put it in a virtual movie made for humans. Not only do they have compound eyes: but they also see much faster than we do.   Movies for humans are projected at 24 frames per second. “For insects to see a movie they need 200 to 300 frames per second,” the professor explains. “Under 200 frames per second they would see the individual images flickering, just like we would at 10 frames per second.”

   So basically, the researchers found a way to tether an apple fly, embed it in a virtual reality world (a film), and then they showed the film at 200-300 frames per second, ten times faster than films made for humans.  And observed the fly’s reactions.

     OK, so why do flies evade swatting?   “They see you coming a lot faster than you see them,” the researcher sums up.   What seems to be rapid motion for us is rather slow motion for flies.

     By the way, the tethering does not harm the flies. They are treated humanely.

     So the next time you try to swat a fly, keep this in mind. Evolution has equipped them with remarkable vision. Far faster than ours. It’s no contest. The fly will beat you, nine times out of nine.  

Blog entries written by Prof. Shlomo Maital

Shlomo Maital
May 2020
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