Attractor nymphs are patterns that may not specifically represent an insect, yet still elicit a strike from a fish.  Also referred to as prospecting nymphs, the following patterns can be very effective under a number conditions, not limited to: Pressure water, stocked trout, high water conditions (including off-color) ,and fast water such as riffles.  These patterns are both fun to tie and fish, hence why they've earned a spot in my box!