Crayfish, or also called crawdads are a common food source for many freshwater fish, especially bass. But in rivers and lakes where trout get predatory, they will also eat crayfish as well. Therefor a crayfish pattern should be in your box when going out fishing areas where you know crayfish are present. Crayfish offer a large protein meal for fish, and therefor they love eating them. And they are a food source that is year round, instead of some nymph, and dry fly patterns for bass and trout.
This crayfish pattern is one that has probably been done many times before. However I could not find a specific name for it. Its simple, and relatively easy to tie. It also sinks quickly to the bottom and rides hook point up. You could even make this more barbless by putting a mono weed guard on the front. However I find that the fly is quite weedless already with the tag of zonker strip covering the hook point, so I usually don't tie a mono weed guard on. What I like about this fly though is how the claws will splay out after it hits the bottom of the lake or river, and the fly itself angles upward, like a crawdad will do when in defensive mode. Warry bass and trout will sit and watch a crawdad for a few seconds on the bottom, and this subtle movement of the rubber legs and claws will initiate a strike from even the most skittish fish.
Another thing about this fly is that it is relatively inexpensive to tie. It uses a smalll amount of materials, and one bag of rabbit strips will tie 20+ of these flies. Add a body of chenille, which is also inexpensive, a hook, some rubber legs and the dumbbell eyes, and this is a fly that can be tied for under a dollar each. Making it not only effective, quick to tie, but also easy on the wallet.
A easy to follow fly tying video of a Zonker style pattern for trout or bass.
Crayfish are a very important food source for many freshwater species.