SRI Caddis Larva - Larva & Pupa. The SRI Caddis Larva is a variation of the popular Caddis Larva. Caddis Larva are common in most rivers you just have to pick up a rock and you should find them. There are more than 10'000 species of Caddis fly and three stages of metamorphosis for fly fishermen to replicate. Our SRI Caddis Larva fly a good general sub surface imitation that will cover a wide variety of Caddis flies at their first stage of development.