There is a space between the bathroom sink and the tiled wall behind. A crafty spider spins his web across the space, let us call it an opening into the spider's lair. The spider's web follows a diagonal up and down movement (as if the spider were sewing cross stitch!) and broaches the opening just beautifully. Occasionally a hapless moth rests his weary legs on the web and the spider scuttles out of his lair and watches the moth battle to release himself from the silky snare. The spider waits patiently and then carries the corpse away, down into his hidden home.
That spider could solve your moth problem so do think twice before throwing him out.