The latest craze in fly tying is the Czech Nymph, and if you read the articles, they represent an immature caddisfly. I am having difficulty telling where a caddis larva ends, and a caddis pupa starts. They both look the same to me in the photos I have looked at.

Also if a caddis adult (dry fly) is a size 14 or 16 hook, what size should the pupa or larva hook be in relation to the insect?

A. Response: You're right about the life stages; even the Orvis catalog advertises "Caddis Nymph" flies. I suspect that much of this is based on the fact that fishing immature insect imitations is generically called "nymphing," even if you're imitating a larva. A quick note: pupa is singular and pupae is plural; same for larva and larvae.

Caddis larvae are active organisms, found living in portable or fixed cases, or as free-living forms without cases. When the last larval instar begins to pupate into the pupal form, they generally spin a silk case around their bodies and seal themselves off from external influences. There is some debate on the purpose of the pupal life stage, but it is most generally accepted that it is in this form that they develop wings and other features necessary for life out of the water.

Hook size is a hard subject to address. Adult caddis range from 2 to over 40 mm in length and the immatures are about the same. Thus, hook size could range down to a size 24 or smaller if you were trying to imitate some of the microcaddis. Hooks for immatures would pretty much correspond to their body size.