Once flies get indoors, they usually head straight for the bright light of a window thinking this is a way back outside. Catchmaster® Window Fly Traps are designed to be placed directly on windows to capture flies and other flying insects that tend to gather there. The Window Fly Trap is coated with specially formulated adhesive to catch flies. The trap features a thin, adhesive strip on back that is easy to apply and remove directly from windows. Trap flies where they hang out most!