Scuds are important to fish of all sizes and is often a large part of the biomass within a lake or river. They prefer still, or slow moving waters. Most species of Scuds prefer living in shallow water, and that is one of the key factors to why they are important when fly fishing. Studies show that in many waters, scuds make up around 20% of the fish diet. It’s simple really, think scuds and catch fish. We recommend that you use a J:son Swivel for all your fly fishing, no matter what type of fly you are using. However, it is necessary to use a J:son Swivel whenever you fish a size 1 or 2 J:son fly.