This link shows the bug; http://www.worleybuggerflyco.com/ins...stoneflies.htm
This link is a good pattern that I use in the Smokys a lot; http://www.oldsmoky.com/YelSally.htm
Another good pattern is to tie a yellow bodied EHC, but don't palmer the hackle down the whole body. Also, this time of year they are laying eggs so ty a bright red butt on the end of the fly to simulate the egg. Hope this helps.