The caddis fly nymph protects itself by attaching objects to itself such as sand or small wood debris like spruce needles. This makes them easily recognizable in the stream. If you notice a very small ball of sand moving along the bottom where there is no current it's not your imagination, it's a caddis fly nymph. The Cased Caddis Fly Nymph imitates this stage of the caddis flies life cycle. Sizes#12,#14.