Catch flies "psychologically"
Obviously, flies can not respond simultaneously to two equal dangers. We use this mercilessly to catch them.
If the fly is sitting on a surface (eg wall or table), then you must approach the open palms near the surface evenly from both sides of the fly. Important: the palms have to be illuminated approximately equally bright, thus representing two equivalent dangers for the fly. Since she remains as petrified squat, sure she can not decide with her minibrain brain, which of the two dangers she should avoid.
Are the hands only about 25 cm apart, then quickly clap together and you have them. Then only dispose of fly-like and wash hands.
For lack of mosquitoes, I could not test whether they react that way.
