The Bead Head Scud Nymph is a great scud/shrimp imitation, and it is widely used in all types of bodies of water. They can be fished as a dropper fly or by themselves, they are commonly used on euro rigs as well.
Zinger Fishing includes 3 of these bad boys in our best selling nymph kit. Fly fishing anglers utilize this fly pattern quite frequently. If you aren't already using them, then I suggest adding a few to your arsenal.