The engine of the fly is absolutely fascinating. They have two types of flight muscle: the so-called power muscle, which is stretch-activated, meaning that it activates itself and does not need to be controlled on a contraction-by-contraction basis by the nervous system. It’s specialized to generate the enormous power required for flight, and it fills the middle portion of the fly. So when a fly hits your windshield, it’s basically the power muscle that you’re looking at.
Attached to the base of the wing is a set of little, tiny control muscles that are not very powerful at all, but they’re very fast, and they’re able to reconfigure the hinge of the wing on a stroke-by-stroke basis, and this is what enables the fly to change its wing and generate the changes in aerodynamic forces which change its flight trajectory. And of course, the role of the nervous system is to control all this.
You’ll never look at a fruit fly the same way again.