Caddis Nymph Flies are actually usually Caddis Larva or Caddis Pupa imitations since there is technically no "nymphal" stage in the Caddisfly's development. Caddis Larvae and Caddies Pupae are present in large numbers in most trout streams and they are an important part of the diet of most trout. Most Caddisfly Larva build a protective case around themselves out of sand, small rocks, or sticks and leaves. A few species of Caddisflies are actually free-swimming in the larval stage. These Caddis Nymph imitations are sure to become some of your go-to nymph patterns.