Hans Wielenmann has an interesting pattern on this site called the F Bug. In answer to a question about the fly's purpose/imitation, Hans explained that the original is a general purpose emerger - as well as a searching pattern.

We have long had what folks refer to as "attractor" patterns. However, most of these flies were bright in color and/or had some sort of flash. I am thinking of a Royal Wulff or a Renegade, etc.

These patterns were often used when there were no insects hatching or on the water. The theory is that they might induce a strike. But, they were tied to have a general similarity with the shape of insects and had "triggers" which might induce a strike.

Do others use "searching" patterns similar to Hans' F Bug?