Created by Gary LaFontaine, it is one of the best caddis pupa patterns ever. I have done very well with this fly for over 40 years. The secret is the antron yran which has tri-lobal fibers the reflect light the same way the insects air sac does. The pupa inflates the sac around its body with air to help it ascend to the surface then it pops out as an adult. This fly is to be fished just under the surface.