I seem to have no problem killing them when they fly on my windows and stop moving. I swat their ass and bury them before they even know what happened. My record is 262-12 (been keeping track for three years).
Matt, thanks for the great post. What's our legal liability if we maim or kill the fly?
Ask a lawyer. I'd recommend one specializing in criminal cases involving insect injury. Should have their own category in any Yellow Pages.
try this out: with your hands fairly far apart (so as not to alert the fly), clap very hard (and quickly) about 4 inches above where the fly is -- whether their escape route is front/back/left/right it almost certainly involves going up...this works great, seriously.
What if you don't want to smash a fly in your hands?
If you use only one hand you can catch the fly (alive) inside your hand (need some training) then you open the window and let it go.
I always get a mystic sense of pride when I manage to capture a fly alive with my hand. It's like I'm a ninja of some sort. Of course the worst part is figuring out if you caught the fly without letting it go. I can never tell if it's in may hand or if it got away until after I open my hand.
I only do that for spiders. Flies not so much.
Or feed it to your lizards, like my friend used to do.
My girlfriend was slightly distraught the other day because she had swatted two flies while they were having sex. I guess researchers have some more work to do analysing how various movements contribute to life and death :-)
It's because they can detect the tiny air pressure changes from nearby moving objects. The trick to swatting a fly is simply to swing hard and fast. If you half-ass it they sense the incoming palm/magazine/swatter while they have plenty of time to react.