My approach to tying shrimps and Czech nymphs is very similar. Take the basic process and make alterations to the ingredients, and you have a huge range of possibilities for your river fly box. In addition to this version, be sure to check out my other Gammarus imitation.
I have changed the way I tie the pattern. Originally I used monofilament ribs exclusively and always tied the shell back in first. The dubbed body was usually formed with dubbing noodled around the thread and the choice of materials often synthetic. I also now prefer to tie the rib with my working thread.
I believe that the tutorial shown opposite is not only a faster approach to tying, but creates a neater, slimmer fly. Using natural materials (or naturals blended with synthetics) also works better. The fish will of course always have the final word - but they don't seem to be complaining! Experiment with materials and see which work for you. As for the shell back, I am using either Wapsi Thin Skin (or similar) or raffine. Raffine (raffia, swiss-straw) may tear easily in one direction, but it is very strong in the other. With a coat of varnish or UV cure resin over it too, it is very durable. The range of effects you can achieve with it makes it a useful alterative to the usual shell-back materials.
The materials used for the pattern in the tutorial are:
Hook: Partridge SHR Barbless Shrimp #14
Ballast: Flat lead
Thread: Moser Powersilk 10/0 olive
Shell Back: Wapsi Thin Skin
Legs / body: Rabbit
Hotspot: Hare, dyed orange
Rib: Tying thread
I have included a hot spot in this example - easy to apply with just a change of dubbing. Gammarus will sometimes act as an intermediate host, carrying a parasite which manifests itself to give the shrimp a orange 'spot' in the body. The parasite makes the shrimp behave unnaturally resulting in them being readily taken by fish - the parasite's next host.
Adding the hotspot is very much optional - but it gives yet another variation which, on its day, can make all the difference
Tied with two layers of lead, the shrimp pattern can still remain slim:
These examples are tied with Hends Spectra-blend for the shell back. This maeterial is quite bright. Hwever a bright, flashy imitation can sometimes be useful.
Th shell back has a very realistic effect. Also notice the offset point of the Partridge Czech Nymph hooks. This is a CZF Fine Wire #12.
A pink nymph is useful in armoury for when targetting grayling: