This is my second favorite nymph in terms of fish appeal. This works on bass, trout, sunfish, you name it. If it eats insects, it will go after this simple to tie fly.
Hook: Mustad 7957B 10-16
Body: Rabbit under fur
Throat: Rabbit guard hair
Thread: Monochord 3/0
This is such a simple fly, it's almost cheating, but it works so incredibly well, almost as well as my sable nymph. And Rabbit fur is easier to find than sable. Tying is sheer simplicity. Wrap a foundation from eye to bend, dub the thread with rabbit fur and wrap, then tie in the throat, about twenty strands that reach the tip of the hook on average, some shorter, some longer. Finish with a wrap knot. Make about thirty of them in subtle color ranges, from light ginger to pale olive to darker browns. Make some uniform and some mottled. The wider the range of color and size, the more effective the collection will be on the water.
The caddis puppa is present in most US waters throughout the warm months, from early spring to late fall. As long as you're not iced out, it is a fly that will work with regularity all season long. The guard hairs from the rabbit are quite flexible and supply ample motion to attract fish into striking. There doesn't need to be a hatch in progress for these flies to work, since half of the caddis species do not conform to a hatch. During a hatch, fine tuning color and size is more important than when there is no hatch in progress. Hatches are most likely to occur in late spring and early summer. The rest of the year, it imitates the other species of caddis that don't follow a specific hatch.
For fish not oriented to hatches, this fly is instant attraction. In still water, the best action is a slow rise and fall, like a puppa in the process of hatching, gaining air pockets in the skin being shedded, then losing it to the pressure differentiation and sinking again. It's a slow retrieve that works best. But at the same time, a faster retrieve is also effective, imitating other water-oriented lifeforms that swim instead of rise. This is just one of those flies that never fails to attract bites, short of a case of absolute lock jaw. It also works quite well around structure, the throat acting as a natural weedguard.
It's hard to praise it enough, simple and inexpensive to tie in bulk quantities, versitile and consistently effective on the water. I always have a good stock of these in my fly box. I never cry at losing them and love catching fish with them.