I'm looking for a book that comprehensively covers the bugs we have in the PNW (or U.S) in larval and adult stages and the flies that match the bugs. Any recommendations?
Yes, Hatch Guide For Western Streams by Jim Schollmeyer offers a color photo of each covered insect life stage on the left page, and three effective imitations on the right page. Insects covered are as follows: Mayflies Blue-Winged Olive (Family: Baetidae, Genus: Baetis) Swimmer Speckle-Wing Quill (Family: Baetidae, Genus: Callibaetis) Swimmer Ameletus (Family: Ameletidae, Genus: Ameletus) Swimmer Black or Gray Drake (Family: Siphlonuridae, Genus: Siphlonurus) Swimmer Pale Morning Dun (Family: Ephemerellidae, Genus: Ephemerella) Crawler Western Green Drake (Family: Ephemerellidae, Genus: Drunella) Crawler Flav (Family: Ephemerellidae: Genus: Drunella) Crawler Slate-Winged Olive (Family: Ephemerellidae, Genus Drunella) Crawler Mahogany Dun (Family: Leptophlebiidae, Genus: Paraleptophlebia) Crawler Trico (Family: Leptohyphidae, Genus: Tricorythodes) Crawler Western March Brown (Family: Heptageniidae, Genus: Rhithrogena) Clinger Pale Evening Dun (Family: Heptageniidae, Genus: Heptagenia) Clinger Yellow Quill (Family: Heptageniidae, Genus: Epeorus) Clinger Blue-Winged Red Quill (Family: Heptageniidae, Genus: Cinygmula) Clinger Brown Drake (Family: Ephemeridae, Genus: Ephemera) Burrower Big Yellow May (Family: Ephemeridae, Genus: Hexagenia) Burrower Caddisflies Green Rock Worm (Family: Rhyacophilidae, Genus: Rhyacophila) Free-Living Spotted Sedge (Family: Hydropsychidae, Genus: Hydropsyche) Netspinning Glossosoma (Family: Glossosomatidae, Genus: Glossosoma) Saddlecase American Grannom (Family: Brachycentridae, Genus: Brachycentrus) Tubecase Little Western Weedy-Water Sedge (Family: Brachycentridae, Genus: Amiocentrus) Tubecase Fall Caddis (Family: Limnephilidae, Genus: Dicosmoecus) Tubecase Stoneflies Giant Salmonfly (Family: Pteronarcyidae, Genus: Pteronarcys) Golden Stoneflies (Family: Perlidae, Genus: Hesperoperla or Calineuria) Little Brown Stoneflies (Family: Nemouridae, Genus: Nemoura) Little Green Stoneflies (Family: Chloroperlidae, Genus: Alloperla or Sweltsa) Little Yellow Stoneflies (Family: Perlodidae, Genus: Isoperla) Midges (Family: Chironomidae)
I'd like to second Roger's recommendation and to note that Jim has a similar book, Hatch Guide for Lakes that covers the same area of information for the stillwater angler (Yes Virginia, there are flies for lake fishing other than chironomids and woolly buggers). If you want to know a lot more about mayflies, check out Hughes and Hafele's Western Mayfly Hatches.