Want to strangle that pesky fly that keeps buzzing around you?
Even if you could find a rope small enough, you can't choke a fly because insects breathe quite differently from us.
They don't have a central area such as our lungs where they gather oxygen, nor a transport system such as our heart and the blood it uses to deliver oxygen to all of our cells. Nope, flies, like all insects, breathe through many tiny openings called spiracles.
These openings are part of tubes called trachea. Each tube leads to a fluid-filled tracheole, where the oxygen dissolves and then diffuses across the wall of the tracheole and into several of the insect's cells. So there is no central breathing area to block off so that you might strangle a fly.
However, if you wanted to drown a fly, that's another story. The spiracles of most insects can close to keep things such as dust out. Therefore, they can hold their breath, so to speak. But if an insect is trapped in water for too long, it will run out of oxygen and eventually drown.
How do flies breathe? (HowStuffWorks)