How many eyes does a fly have? The eye of the fly

I’m sure this situation sounds familiar to you. There’s a fly in the room, buzzing around, taking its time… and you either don’t want to use fly spray or you have something to hand that you think will swat it effectively. It’s a fun game, but one that you can rarely win because the fly always takes off just as you begin your killer swing.

House flies have the advantage over their predators. They have five eyes; three rudimentary eyes on top of their heads and two large compound eyes (the bulbous eyes that we notice first). The compound eyes are hemispheres which protrude above the surface of the head, each hemisphere covered with thousands of vision receptors called ommatidia. Each receptor works as an eye, giving the fly thousands of images with all-round vision of the world beside and above it. Unless you creep up on it from below, the fly will see you (and it’s impossible to swat a fly from below). Flies are short-sighted, but even a short-sighted creature will see movement in time to escape.

The fly eye has one further advantage. Research carried out in 2012 by Professor Hardie and Dr Franze from Cambridge University found that fly eyes transmit those images by an electrical impulse, unlike the chemical responses in human eyes – giving the fly its view of the world five times faster than human sight.

How many eyes does a house fly have? Thousands. Each one is faster than yours. Pass the fly spray.