Simple flies are the bread and butter and workhorses for most guides. There is nothing a guide wants to do less of after a long day guiding on the water than spending several hours at night at their vises grinding out a pile of flies for the next days trip. Over time, most guides develop or borrow a number of patterns that fall into the category of guide flies; simple, effective patterns that take maybe a couple of minutes to tie.
Most guide flies in the trout realm will habitually fall into the category of nymphs, but any type of fly be it a streamer, dry or wet fly can fit into this category. What is also a great byproduct of their simplicity in design is you most certainly won't feel that bad if you or your client make an errant cast into the bushes, hang bottom or lose one on a good fish. Well, minus that last example.
The Rats Nest is a fly that slides into the guide flies category nicely. Crane fly larva are an often very overlooked food form for trout, especially when the water has risen as these morsels will habitually get kicked into the drift. They are nothing more than a midge larva on steroids so replicating them is rather easy. The Rats Nest however is more than a weighted nymph pattern. You see this simple tie has an alter ego of sorts as she can easily be manipulated like a streamer with great success. I will often tie one of these on by itself or trailing behind another larger streamer when the bite is rather slow and the Rats Nest will always save an otherwise tough day. Tie a few up and add them to your rotation.