House building caddis larva are available in most waters all year round, and are an important segment of the diet of trout and grayling. There are many techniques that have been developed over the years from fly tying benches all over the world to imitate the house of the caddis larva, but this technique really gives the right impression. This is a pattern I believe was developed in the US, but other than that I cant find any other information about it. The great thing about this pattern is if you trim the rubber legs close to the body you get the impression of a caddis larva house built out of gravel, but if you spin the rubber legs not so tight and trim them a little longer it makes for a great house made of vegetation and sticks. Also the rubber gives that extra needed weight when you need to get down deep and not least extremely durable.
You may find that this isn´t the easiest pattern to tie at the first attempt as the rubber legs seem to have a life of their own, but after a few attempts is no more difficult then any other pattern. Try mixing colours and rubber types to achieve different effects.